Consequences of trisomy 21 for brain development in Down syndrome

Evidence from induced pluripotent stem cells differentiated to ventral forebrain-like interneuron progenitors indicates that the number of progenitors produced is different in the presence of trisomy 21.

“Evidence from iPSCs differentiated to ventral forebrain-like interneuron progenitors indicates that the number of progenitors that are produced is different in the presence of T21 (84,90,91).”

• cites [84] Giffin-Rao, Y. et al. Altered patterning of trisomy 21 interneuron progenitors. Stem Cell Rep. 17, 1366–1379 (2022). sourceSupported
• cites [90] Huo, H. Q. et al. Modeling Down syndrome with patient iPSCs reveals cellular and migration deficits of GABAergic neurons. Stem Cell Rep. 10, 1251–1266 (2018). sourceDisputed

  The Discussion states that cortical inhibitory neural progenitors are generated similarly from Down syndrome and euploid iPSCs, contrary to the claimed difference in progenitor production. The Results likewise report similar efficiency in generating GABAergic interneurons, while identifying differences in their morphology. (LLM, conf=0.90)

  Checked by a reasoning model — may be wrong.

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• cites [91] Xu, R. et al. OLIG2 drives abnormal neurodevelopmental phenotypes in human iPSC-based organoid and chimeric mouse models of Down syndrome. Cell Stem Cell 24, 908–926.e8 (2019). This study shows that trisomy 21 iPSCs overproduce OLIG2+ ventral forebrain neural progenitors and GABAergic neurons in organoids and in chimeric mouse brains. sourceSupported

Studies on the post-mortem Down syndrome brain are often underpowered because of limited availability of human brain tissue, especially from prenatal developmental periods.

“Because of the limited availability of human brain tissue, especially from prenatal developmental periods, studies on the post-mortem DS brain are often underpowered17.”

• cites [17] Risgaard, K. A., Sorci, I. A., Mohan, S. & Bhattacharyya, A. Meta-analysis of Down syndrome cortical development reveals underdeveloped state of the science. Front. Cell Neurosci. 16, 915272 (2022). sourceSupported

Neurodevelopmental impairment and neuronal dysfunction contribute to the hallmark cognitive deficits observed in individuals with Down syndrome.

“There is evidence that neurodevelopmental impairment and neuronal dysfunction contribute to the hallmark cognitive deficits observed in individuals with DS8,9.”

• cites [8] Menghini, D., Costanzo, F. & Vicari, S. Relationship between brain and cognitive processes in Down syndrome. Behav. Genet. 41, 381–393 (2011). This study has compared grey matter density in adolescents with Down syndrome to controls and has correlated the data with neuropsychological measures. sourceNot checked — no full text of the source
• cites [9] Carducci, F. et al. Whole-brain voxel-based morphometry study of children and adolescents with Down syndrome. Funct. Neurol. 28, 19–28 (2013). sourceSupported

Human induced pluripotent stem cells generated from somatic cells of individuals with Down syndrome provide another approach to interrogate the cellular and molecular mechanisms underlying altered neural development in human cells.

“Human induced pluripotent stem cells (iPSCs) generated from somatic cells of individuals with DS provide another approach to interrogate the cellular and molecular mechanisms underlying altered neural development in human cells28 (Boxes 1 and 2).”

• cites [28] Zhao, X. & Bhattacharyya, A. Human models are needed for studying human neurodevelopmental disorders. Am. J. Hum. Genet. 103, 829–857 (2018). sourceSupported

Mouse models have allowed advances in deciphering mechanisms governing brain development and function and the consequences of Down syndrome-related manipulations.

“These models have allowed the scientific community to make incredible advances in deciphering the mechanisms governing brain development and function, as well as the consequences of DS-related manipulations for those mechanisms18–22.”

• cites [18] Freeburn, A. & Munn, R. G. K. Signalling pathways contributing to learning and memory deficits in the Ts65Dn mouse model of Down syndrome. Neuronal Signal. 5, Ns20200011 (2021). sourceSupported
• cites [19] Ishihara, K. Genes associated with disturbed cerebral neurogenesis in the embryonic brain of mouse models of Down syndrome. Genes 12, 1598 (2021). sourceSupported
• cites [20] Moyer, A. J., Gardiner, K. & Reeves, R. H. All creatures great and small: new approaches for understanding Down syndrome genetics. Trends Genet. 37, 444–459 (2021). sourceSupported
• cites [21] Tosh, J., Tybulewicz, V. & Fisher, E. M. C. Mouse models of aneuploidy to understand chromosome disorders. Mamm. Genome 33, 157–168 (2022). sourcePartly supported

  The “Current mammalian models of aneuploidy” section (page unavailable) describes how Down syndrome mouse models reveal effects of gene-dosage manipulations on behaviour and cognition, supporting the brain-function portion of the claim. Our copy does not show that these models have deciphered mechanisms governing brain development; it also notes that existing models cannot isolate the effects of aneuploidy itself from gene dosage. (LLM, conf=0.82)

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• cites [22] Haydar, T. F. & Reeves, R. H. Trisomy 21 and early brain development. Trends Neurosci. 35, 81–91 (2012). sourceSupported

Gross anatomical differences in brain structure are apparent in fetal and neonatal brains of individuals with Down syndrome, including reductions in overall brain volume, white matter volume, gyral complexity, sulcal depth and growth of the cortical plate.

“Gross anatomical differences in brain structure are apparent in the fetal and neonatal brains of individuals with DS, including reductions in overall brain volume, white matter volume, gyral complexity, sulcal depth and growth of the cortical plate6,8–15.”

• cites [6] Fukami-Gartner, A. et al. Comprehensive volumetric phenotyping of the neonatal brain in Down syndrome. Cereb. Cortex 33, 8921–8941 (2023). sourcePartly supported

  The Results section reports smaller whole-brain and cerebral white-matter volumes in neonates with Down syndrome. The Discussion also reports reduced fetal whole-brain volume and lower sulcal depth and gyrification index from earlier studies. Our copy does not establish reduced growth of the cortical plate, so that element of the attributed claim is unsupported. Page numbers are unavailable in the indexed passages. (LLM, conf=0.86)

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• cites [8] Menghini, D., Costanzo, F. & Vicari, S. Relationship between brain and cognitive processes in Down syndrome. Behav. Genet. 41, 381–393 (2011). This study has compared grey matter density in adolescents with Down syndrome to controls and has correlated the data with neuropsychological measures. sourceNot checked — no full text of the source
• cites [9] Carducci, F. et al. Whole-brain voxel-based morphometry study of children and adolescents with Down syndrome. Funct. Neurol. 28, 19–28 (2013). sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

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• cites [10] Baburamani, A. A., Patkee, P. A., Arichi, T. & Rutherford, M. A. New approaches to studying early brain development in Down syndrome. Dev. Med. Child Neurol. 61, 867–879 (2019). This paper reviews recent advances in magnetic resonance imaging that allow non-invasive visualization of the macrostructure and microstructure of the fetal and neonatal Down syndrome brain. sourcePartly supported

  Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

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• cites [11] Baburamani, A. A. et al. Assessment of radial glia in the frontal lobe of fetuses with Down syndrome. Acta Neuropathol. Commun. 8, 141 (2020). sourcePartly supported

  Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

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• cites [12] McCann, B. et al. Structural magnetic resonance imaging demonstrates volumetric brain abnormalities in Down syndrome: newborns to young adults. Neuroimage Clin. 32, 102815 (2021). sourcePartly supported

  The Discussion reports smaller absolute brain volumes and reduced white-matter volumes in several regions in the Down syndrome cohort; it also cites other studies finding abnormal fetal brain development. This paper's own age cohorts begin at birth, and the passages do not establish reduced gyral complexity, sulcal depth, or cortical-plate growth in fetal or neonatal brains. The copy provides no page numbers for these passages. (LLM, conf=0.86)

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• cites [13] Tarui, T. et al. Quantitative MRI analyses of regional brain growth in living fetuses with Down syndrome. Cereb. Cortex 30, 382–390 (2020). sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

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• cites [14] Yun, H. J. et al. Regional alterations in cortical sulcal depth in living fetuses with Down syndrome. Cereb. Cortex 31, 757–767 (2021). sourcePartly supported

  The Abstract and Discussion report reduced average sulcal depth and gyrification in fetuses with Down syndrome. The Introduction describes altered cortical-plate growth and cites smaller brains and reduced white-matter volume in children, but does not establish all those reductions in fetuses or neonates. The Discussion specifically says a previous fetal study found no difference in whole-brain volume. (LLM, conf=0.90)

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• cites [15] Shiohama, T., Levman, J., Baumer, N. & Takahashi, E. Structural magnetic resonance imaging-based brain morphology study in infants and toddlers with Down syndrome: the effect of comorbidities. Pediatr. Neurol. 100, 67–73 (2019). sourcePartly supported

  The Discussion reports reduced cerebellar gray-matter volume at birth, and the Results report reduced right cerebellar white-matter volume in infants and toddlers with Down syndrome. But the Results find no statistically significant difference in total intracranial or cortical white-matter volume. The paper does not establish the claimed fetal reductions in gyral complexity, sulcal depth, or cortical-plate growth. Page numbers were not available in our copy. (LLM, conf=0.88)

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Neuroanatomical evidence alone is insufficient to explain the neurodevelopmental deficits and biological processes that drive intellectual disability in Down syndrome.

“However, this neuroanatomical evidence is insufficient on its own to explain the neurodevelopmental deficits and biological processes that drive intellectual disability16.”

• cites [16] Hamner, T., Udhnani, M. D., Osipowicz, K. Z. & Lee, N. R. Pediatric brain development in Down syndrome: a field in its infancy. J. Int. Neuropsychol. Soc. 24, 966–976 (2018). sourcePartly supported

  The Summary of DS Imaging Findings says existing studies cannot yet provide a developmentally informed model of brain development in Down syndrome. The State of the Literature conclusion likewise says the lack of longitudinal imaging limits understanding of how neuroanatomic and cognitive-behavioral phenotypes unfold. These passages support the insufficiency of current neuroanatomical evidence, but do not specifically establish what biological processes drive intellectual disability. (LLM, conf=0.79)

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The underlying biological mechanisms that lead to altered formation of the cortex in individuals with Down syndrome may not be reflected in existing mouse models owing to differences in neurodevelopment across species.

“Moreover, the underlying biological mechanisms that lead to altered formation of the cortex in individuals with DS may not be reflected in the mouse models that do exist, owing to differences in neurodevelopment across species23–27.”

• cites [23] Sousa, A. M. M., Meyer, K. A., Santpere, G., Gulden, F. O. & Sestan, N. Evolution of the human nervous system function, structure, and development. Cell 170, 226–247 (2017). sourcePartly supported

  The Developmental Mechanisms section (page unavailable) describes differences between human and non-primate cortical development. Functional Modeling (page unavailable) says species differences complicate interpretation of mouse studies. These passages support the general caution, but the paper does not establish that existing Down syndrome mouse models fail to reflect mechanisms of altered cortical formation in people with Down syndrome. (LLM, conf=0.82)

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• cites [24] Sherwood, C. C., Bauernfeind, A. L., Bianchi, S., Raghanti, M. A. & Hof, P. R. Human brain evolution writ large and small. Prog. Brain Res. 195, 237–254 (2012). sourceNot checked — no full text of the source
• cites [25] Silbereis, J. C., Pochareddy, S., Zhu, Y., Li, M. & Sestan, N. The cellular and molecular landscapes of the developing human central nervous system. Neuron 89, 248–268 (2016). This comprehensive review highlights the molecular and cellular processes of the developing human CNS, with focus on the cerebral neocortex. sourcePartly supported

  The Introduction (page not available in our copy) says animal models cannot fully reproduce human neurodevelopment or disorders and describes interspecies differences in cortical development. It does not specifically address Down syndrome, altered cortical formation in people with Down syndrome, or existing Down syndrome mouse models. (LLM, conf=0.83)

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• cites [26] Lui, J. H., Hansen, D. V. & Kriegstein, A. R. Development and evolution of the human neocortex. Cell 146, 18–36 (2011). sourcePartly supported

  The Introduction says that species differences limit how well rodent neocortices can model human cortical development. It does not address Down syndrome or test whether existing Down syndrome mouse models reflect the mechanisms of altered cortical formation. (LLM, conf=0.84)

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• cites [27] Geschwind, D. H. & Rakic, P. Cortical evolution: judge the brain by its cover. Neuron 80, 633–647 (2013). sourcePartly supported

  The sections on neoteny and human cortical lamination describe differences in cortical development and gene-expression patterns across species, including humans and mice. The paper does not address Down syndrome or establish that existing Down syndrome mouse models fail to reflect the mechanisms of altered cortical formation. (LLM, conf=0.84)

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Evidence for specific deficits in late-born upper-layer neurons in Down syndrome from observations of post-mortem tissue suggests that specific temporally defined progenitors are affected.

“Evidence for specific deficits in late-born upper-layer neurons in DS from observations of post-mortem tissue further suggests that specific temporally defined progenitors are affected41,84.”

• cites [41] Golden, J. A. & Hyman, B. T. Development of the superior temporal neocortex is anomalous in trisomy 21. J. Neuropathol. Exp. Neurol. 53, 513–520 (1994). This analysis of stereological cell counts performed in one neocortical area during gestation in normal development and in trisomy 21 suggests that the emergence of lamination is disrupted in trisomy 21. sourceNot checked — no full text of the source
• cites [84] Giffin-Rao, Y. et al. Altered patterning of trisomy 21 interneuron progenitors. Stem Cell Rep. 17, 1366–1379 (2022). sourceSupported

The number of progenitors, identified by their expression of the transcription factor SOX2, is reduced in post-mortem brain tissue from individuals with Down syndrome.

“Furthermore, the number of progenitors, identified by their expression of the transcription factor SOX2, is also reduced in post-mortem brain tissue from individuals with DS11.”

• cites [11] Baburamani, A. A. et al. Assessment of radial glia in the frontal lobe of fetuses with Down syndrome. Acta Neuropathol. Commun. 8, 141 (2020). sourcePartly supported

  The Results report fewer SOX2-positive cells in the outer subventricular zone of Down syndrome fetal brains than in age-matched controls. The claim omits that this finding concerns a specific region and gestational period; the Discussion also calls it inconclusive because of the small number of cases. (LLM, conf=0.84)

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Analyses of fetal brain tissue indicate that there are fewer proliferating cells, as measured by expression of the cell cycle marker Ki67 and of cyclin proteins, in the germinal zones of the hippocampus and cortex in Down syndrome.

“Analyses of fetal brain tissue indicate that there are fewer proliferating cells, as measured by their expression of the cell cycle marker Ki67 and of cyclin proteins, in the germinal zones of the hippocampus and cortex in DS40,42–44,47,50,64.”

• cites [40] Contestabile, A. et al. Cell cycle alteration and decreased cell proliferation in the hippocampal dentate gyrus and in the neocortical germinal matrix of fetuses with Down syndrome and in Ts65Dn mice. Hippocampus 17, 665–678 (2007). sourceNot checked — no full text of the source
• cites [42] Guidi, S. et al. Neurogenesis impairment and increased cell death reduce total neuron number in the hippocampal region of fetuses with Down syndrome. Brain Pathol. 18, 180–197 (2008). sourceNot checked — no full text of the source
• cites [43] Guidi, S., Ciani, E., Bonasoni, P., Santini, D. & Bartesaghi, R. Widespread proliferation impairment and hypocellularity in the cerebellum of fetuses with Down syndrome. Brain Pathol. 21, 361–373 (2011). sourcePartly supported

  The Results (page not supplied) report a previous finding of fewer proliferating cells in fetal Down syndrome hippocampal regions and the ventricular germinal matrix, and identify Ki-67 as a marker of proliferating cells. This paper studies the cerebellum and does not report cyclin-protein measurements in the hippocampus or cortex, so it supports only part of the attributed claim. (LLM, conf=0.86)

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• cites [44] Guidi, S. et al. Abnormal development of the inferior temporal region in fetuses with Down syndrome. Brain Pathol. 28, 986–998 (2018). This study reveals reduced thickness and fewer neurons in the fusiform and temporal gyrus of fetuses with Down syndrome than in those of controls. sourcePartly supported

  The section “Abnormal architecture and reduced neuron number in the FG and ITG of DS fetuses” reports a previously observed reduction in proliferating neural precursors in the germinal matrix of DS fetuses. The Abstract also notes reduced neurogenesis in the hippocampal region. Neither passage says that proliferation in both hippocampal and cortical germinal zones was measured using Ki67 and cyclin proteins. (LLM, conf=0.85)

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• cites [47] Stagni, F. et al. Subicular hypotrophy in fetuses with Down syndrome and in the Ts65Dn model of Down syndrome. Brain Pathol. 29, 366–379 (2019). sourcePartly supported

  The Results report 55% fewer Ki-67-positive cells in the ventricular zone overlying the subiculum of fetuses with Down syndrome than in euploid fetuses, and note a prior Ki-67 finding in the hippocampal ventricular zone. This paper does not report cyclin-protein measurements or a corresponding analysis of cortical germinal zones, so those parts of the claim are not supported by it. (LLM, conf=0.88)

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• cites [50] Stagni, F., Giacomini, A., Emili, M., Guidi, S. & Bartesaghi, R. Neurogenesis impairment: an early developmental defect in Down syndrome. Free Radic. Biol. Med. 114, 15–32 (2018). sourceNot checked — no full text of the source
• cites [64] Stagni, F. et al. Neuroanatomical alterations in higher-order thalamic nuclei of fetuses with Down syndrome. Clin. Neurol. Neurosurg. 194, 105870 (2020). sourcePartly supported

  Section 4.1 (page not supplied) reports earlier findings of reduced neural-progenitor pools in fetal Down syndrome hippocampal and temporal regions. Section 3.4 reports fewer Ki-67-positive cells in this study, but measures the third-ventricle zone and thalamic region, not hippocampal or cortical germinal zones. Our copy does not report cyclin-protein measurements for the claimed regions. (LLM, conf=0.86)

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Defects in specification, proliferation and/or migration together likely result in deficiency of interneurons in Down syndrome.

“Furthermore, interneuron progenitors from T21 iPSCs show reduced migratory ability90 compared to controls, raising the likelihood that defects in specification, proliferation and/or migration together result in deficiency of interneurons in DS.”

• cites [90] Huo, H. Q. et al. Modeling Down syndrome with patient iPSCs reveals cellular and migration deficits of GABAergic neurons. Stem Cell Rep. 10, 1251–1266 (2018). sourceSupported

The transcriptomic study focused on the co-dysregulation of genes associated with oligodendrocyte differentiation and myelination.

“In particular, the study has focused on the co-dysregulation of genes associated with oligodendrocyte differentiation and myelination.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourceSupported

Analyses of neural progenitor cells arising from trisomy 21 induced pluripotent stem cells have provided conflicting data, with some suggesting that apoptosis is increased and others seeing no effect.

“Analyses of NPCs arising from T21 iPSCs have provided conflicting data, with some suggesting that apoptosis is increased74,79,95 and others seeing no effect75,77,81,96.”

• cites [74] Li, Z. et al. Asynchronous excitatory neuron development in an isogenic cortical spheroid model of Down syndrome. Front. Neurosci. 16, 932384 (2022). sourcePartly supported

  The Results section, “Trisomic cortical spheroids display a reduced cortical volume” (page unavailable), reports increased apoptosis-marker staining in trisomic versus euploid spheroids at days 90 and 130, but no significant difference at day 30. The spheroids were derived from iPSCs and contained neural progenitors alongside other cell types; the apoptosis measurement was not specific to progenitor cells, so the NPC-specific wording is not fully supported. (LLM, conf=0.84)

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• cites [79] Hibaoui, Y. et al. Modelling and rescuing neurodevelopmental defect of Down syndrome using induced pluripotent stem cells from monozygotic twins discordant for trisomy 21. EMBO Mol. Med. 6, 259–277 (2014). sourceSupported
• cites [95] Campbell, N. B., Patel, Y., Moore, T. L., Medalla, M. & Zeldich, E. Extracellular vesicle treatment alleviates neurodevelopmental and neurodegenerative pathology in cortical spheroid model of Down syndrome. Int. J. Mol. Sci. 24, 3477 (2023). sourceCould not verify

  Results §2.2 reports no significant difference in NPC proliferation or numbers between trisomic and euploid cortical spheroids, but does not measure NPC apoptosis. Results §2.5 reports increased cell death across untreated trisomic spheroids; it does not establish whether apoptosis in NPCs specifically was affected. Thus our copy cannot verify the no-effect finding for NPC apoptosis attributed to this source. (LLM, conf=0.72)

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• cites [75] Murray, A. et al. Brief report: isogenic induced pluripotent stem cell lines from an adult with mosaic Down syndrome model accelerated neuronal ageing and neurodegeneration. Stem Cell 33, 2077–2084 (2015). sourcePartly supported

  The Results report no increase in the proportion of nonviable T21 neural progenitor cells, supporting the cited paper's placement among studies finding no increase in cell death. The passage does not report a direct measure of apoptosis, so it does not fully establish the more specific claim of no effect on apoptosis. (LLM, conf=0.82)

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• cites [77] Tang, X. Y. et al. DSCAM/PAK1 pathway suppression reverses neurogenesis deficits in iPSC-derived cerebral organoids from patients with Down syndrome. J. Clin. Invest. 131, 135763 (2021). sourceSupported
• cites [81] Weick, J. P. et al. Deficits in human trisomy 21 iPSCs and neurons. Proc. Natl Acad. Sci. USA 110, 9962–9967 (2013). sourceNot checked — no full text of the source
• cites [96] Briggs, J. A. et al. Integration-free induced pluripotent stem cells model genetic and neural developmental features of Down syndrome etiology. Stem Cell 31, 467–478 (2013). sourceNot checked — no full text of the source

In Down syndrome, the appearance of cognitive and neuroanatomical deficits in infancy suggests that the underlying alterations probably emerge during the earliest stages of neural cell specification, synaptogenesis and synaptic transmission.

“In DS, the appearance of cognitive and neuroanatomical deficits in infancy suggests that the underlying alterations probably emerge during the earliest stages of neural cell specification, synaptogenesis and synaptic transmission25.”

• cites [25] Silbereis, J. C., Pochareddy, S., Zhu, Y., Li, M. & Sestan, N. The cellular and molecular landscapes of the developing human central nervous system. Neuron 89, 248–268 (2016). This comprehensive review highlights the molecular and cellular processes of the developing human CNS, with focus on the cerebral neocortex. sourceCould not verify

  The sections on prenatal and postnatal neurodevelopment and neural circuit assembly describe when neural cells develop and synapses form in humans generally. Our copy does not address cognitive or neuroanatomical deficits in infants with Down syndrome, or infer that those deficits arise from alterations in cell specification, synaptogenesis, or synaptic transmission (searched: Down syndrome, trisomy 21, infancy). (LLM, conf=0.72)

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Interneuron progenitors from trisomy 21 induced pluripotent stem cells show reduced migratory ability compared to controls.

“Furthermore, interneuron progenitors from T21 iPSCs show reduced migratory ability90 compared to controls, raising the likelihood that defects in specification, proliferation and/or migration together result in deficiency of interneurons in DS.”

• cites [90] Huo, H. Q. et al. Modeling Down syndrome with patient iPSCs reveals cellular and migration deficits of GABAergic neurons. Stem Cell Rep. 10, 1251–1266 (2018). sourceSupported

Only one comprehensive analysis of human developmental tissue that identifies the molecular and cellular pathways disrupted during brain development in Down syndrome exists.

“Currently, only one comprehensive analysis of human developmental tissue that identifies the molecular and cellular pathways that are disrupted during brain development in DS exists39.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourcePartly supported

  The Discussion describes this as the most comprehensive developmental gene-expression analysis of human Down syndrome brains to date, and the Introduction says earlier studies had important limitations. These passages support identifying the paper as a comprehensive analysis of disrupted developmental processes, but they do not establish the citing sentence’s stronger claim that it is the only one currently in existence. (LLM, conf=0.84)

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BrdU pulse labelling of trisomy 21 induced pluripotent stem cell-derived progenitors revealed that the proportion of neural progenitor cells in S phase of the cell cycle can vary across different stages of their development in vitro.

“Additional evidence, which shows that decreased proliferation of progenitors can lead to the generation of fewer neurons in DS, comes from BrdU pulse labelling of T21 iPSC-derived progenitors, which revealed that the proportion of NPCs in S phase of the cell cycle, the period of protein synthesis before mitosis or cell division, can vary across different stages of their development in vitro65.”

• cites [65] Sharma, V. et al. Biphasic cell cycle defect causes impaired neurogenesis in Down syndrome. Front. Genet. 13, 1007519 (2022). This paper shows that human trisomy 21 iPSCs display abnormal cell cycle features during neural differentiation compared to controls. sourceSupported

Increased numbers of astrocytes have been reported in the fetal brain in individuals with Down syndrome.

“Increased numbers of astrocytes have been reported in the fetal brain in individuals with DS42,44,99 (Fig. 1).”

• cites [42] Guidi, S. et al. Neurogenesis impairment and increased cell death reduce total neuron number in the hippocampal region of fetuses with Down syndrome. Brain Pathol. 18, 180–197 (2008). sourceNot checked — no full text of the source
• cites [44] Guidi, S. et al. Abnormal development of the inferior temporal region in fetuses with Down syndrome. Brain Pathol. 28, 986–998 (2018). This study reveals reduced thickness and fewer neurons in the fusiform and temporal gyrus of fetuses with Down syndrome than in those of controls. sourcePartly supported

  In “Abnormal architecture and reduced neuron number in the FG and ITG of DS fetuses” (page not provided), the paper reports a relative increase in GFAP-positive astrocytes in the fetal hippocampus. But its own FG and ITG results found similar absolute numbers of GFAP-positive cells in DS and euploid fetuses; the increased S100B-positive cells cannot all be identified as astrocytes because S100B also marks other glia. The claim therefore overstates the evidence for increased astrocyte numbers in the fetal brain. (LLM, conf=0.86)

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• cites [99] Zdaniuk, G., Wierzba-Bobrowicz, T., Szpak, G. M. & Stepien, T. Astroglia disturbances during development of the central nervous system in fetuses with Down’s syndrome. Folia Neuropathol. 49, 109–114 (2011).Not checked — no full text of the source

Sleep spindles are disrupted or completely absent in individuals with DS within the first year of life.

“Furthermore, sleep spindles, which are thought to be reflective of memory potentiation and consolidation, are disrupted or completely absent in individuals with DS within the first year of life139.”

• cites [139] Shetty, M., Davey, M. J., Nixon, G. M., Walter, L. M. & Horne, R. S. C. Sleep spindles are reduced in children with Down syndrome and sleep-disordered breathing. Pediatr. Res. 96, 457–470 (2024). sourcePartly supported

  The Results report reduced spindle activity in children with Down syndrome and no recorded spindles in two of them. But the Methods (Subjects; page unavailable) specify that participants were aged 3–19 years, so the paper does not establish that this occurs within the first year of life. The Discussion also describes a proposed role for spindles in memory consolidation. (LLM, conf=0.90)

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Findings from mouse models of Down syndrome, particularly the Ts65Dn model, show reduced long-term potentiation and increased long-term depression, reflecting the relative strengthening and weakening, respectively, of individual synapses.

“This suggestion is largely driven by findings from mouse models of DS, particularly the Ts65Dn model, in which patch clamp electrophysiology analyses reveal reduced long-term potentiation (LTP) and increased long-term depression (LTD), reflecting the relative strengthening and weakening, respectively, of individual synapses123–126.”

• cites [123] Siarey, R. J., Rapoport, S. I. & Galdzicki, Z. Altered long-term potentiation in the young and old Ts65Dn mouse, a model for Down syndrome. Neuropharmacology 36, 1549–1554 (1997). sourceNot checked — no full text of the source
• cites [124] Siarey, R. J. et al. Increased synaptic depression in the Ts65Dn mouse, a model for mental retardation in Down syndrome. Neuropharmacology 38, 1917–1920 (1999). sourceNot checked — no full text of the source
• cites [125] Kleschevnikov, A. M. et al. Increased efficiency of the GABAA and GABAB receptor-mediated neurotransmission in the Ts65Dn mouse model of Down syndrome. Neurobiol. Dis. 45, 683–691 (2012). sourcePartly supported

  The Introduction and Discussion link abnormal synaptic plasticity in Ts65Dn mice to enhanced inhibition, and the References list a study of suppressed hippocampal LTP. But this paper’s electrophysiological results concern GABAergic transmission and paired-pulse responses; our copy does not report increased LTD or show that its recordings measured LTP and LTD. (LLM, conf=0.81)

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• cites [126] Kleschevnikov, A. M. et al. Hippocampal long-term potentiation suppressed by increased inhibition in the Ts65Dn mouse, a genetic model of Down syndrome. J. Neurosci. 24, 8153–8160 (2004). sourcePartly supported

  The section ‘Failed induction of LTP and inadequate synaptic activation of NMDA receptors in Ts65Dn mice’ reports that LTP was not induced in Ts65Dn dentate-gyrus slices. The paper’s LTP measurements used field-potential recordings, while its whole-cell recordings assessed inhibitory currents. Its finding of increased paired-pulse depression reflects stronger feedback inhibition, not increased long-term depression (LTD); no page numbers are available in our copy. (LLM, conf=0.88)

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Cognitive deficits in DS may be the product of impaired network-level function.

“The early developmental onset of these network-level disruptions — which are probably the product of altered synapse formation and function — coincides with the emergence of intellectual disability, suggesting that the cognitive deficits may be the product of impaired network-level function37,140–142.”

• cites [37] Silverman, W. Down syndrome: cognitive phenotype. Ment. Retard. Dev. Disabil. Res. Rev. 13, 228–236 (2007). sourceNot checked — no full text of the source
• cites [140] Frank, K. & Esbensen, A. J. Fine motor and self-care milestones for individuals with Down syndrome using a retrospective chart review. J. Intellect. Disabil. Res. 59, 719–729 (2015). sourceNot checked — no full text of the source
• cites [141] Esbensen, A. J. et al. Outcome measures for clinical trials in Down syndrome. Am. J. Intellect. Dev. Disabil. 122, 247–281 (2017). sourceCould not verify

  The Results > Cognition Domains section describes cognitive deficits in people with Down syndrome, including memory and executive-function difficulties. It does not address whether impaired network-level function produces those deficits; searches for network disruptions, connectivity, and synaptic dysfunction found no passage making that link. Page numbers were unavailable in our copy. (LLM, conf=0.73)

  Experimental — accuracy not yet measured
• cites [142] Faught, G. G., Conners, F. A. & Himmelberger, Z. M. Auditory and visual sustained attention in Down syndrome. Res. Dev. Disabil. 53–54, 135–146 (2016). sourcePartly supported

  The Introduction (page not available) says cognitive abnormalities in Down syndrome are likely related to abnormal brain development and discusses altered brain regions. That supports a broad brain-based explanation, but our copy does not identify impaired network-level function as the mechanism. (LLM, conf=0.81)

  Experimental — accuracy not yet measured

Gene dysregulation and disrupted calcium signalling in glial cells contribute to the synaptic deficits in DS.

“Evidence suggests that gene dysregulation and disrupted calcium signalling in glial cells also contribute to the synaptic deficits131,134.”

• cites [131] Araujo, B. H. S. et al. Down syndrome iPSC-derived astrocytes impair neuronal synaptogenesis and the mTOR pathway in vitro. Mol. Neurobiol. 55, 5962–5975 (2018). sourceNot checked — no full text of the source
• cites [134] Garcia, O., Torres, M., Helguera, P., Coskun, P. & Busciglio, J. A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down’s syndrome. PLoS ONE 5, e14200 (2010). sourcePartly supported

  The Discussion (page unavailable) reports that Down’s syndrome astrocytes contribute to reduced synaptic density, and the Results link this effect to reduced astrocytic TSP-1 protein. The Discussion also notes elevated intracellular calcium in DS astrocytes, but does not establish that disrupted calcium signalling causes the synaptic deficits. It does not establish gene dysregulation as a cause either. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

The formation of new synapses and establishment of dendritic spines becomes increasingly rapid over the course of late fetal and early postnatal development but tapers off around the age of 2 years.

“The formation of new synapses and establishment of dendritic spines becomes increasingly rapid over the course of late fetal and early postnatal development but tapers off around the age of 2 years (112–114).”

• cites [112] Huttenlocher, P. R. Synaptic density in human frontal cortex — developmental changes and effects of aging. Brain Res. 163, 195–205 (1979). sourceNot checked — no full text of the source
• cites [113] Huttenlocher, P. R. & Dabholkar, A. S. Regional differences in synaptogenesis in human cerebral cortex. J. Comp. Neurol. 387, 167–178 (1997). sourceNot checked — no full text of the source
• cites [114] Petanjek, Z. et al. Extraordinary neoteny of synaptic spines in the human prefrontal cortex. Proc. Natl Acad. Sci. USA 108, 13281–13286 (2011). sourcePartly supported

  The Results (p. 2) report that dendritic spine density increased significantly during infancy and peaked in childhood. The Results (p. 3) place the highest values at ages 2.5–7 for layer IIIc neurons and 7–9 for layer V neurons. The paper does not establish an increasingly rapid rate of formation during late fetal development or a general tapering at age 2. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

Neurons generated from iPSCs derived from individuals with DS have little to no capacity for either LTP or LTD in vitro.

“Moreover, neurons generated from iPSCs derived from individuals with DS have little to no capacity for either LTP or LTD in vitro132, and when transplanted into the mouse brain, these neurons have reduced structural plasticity relative to controls133.”

• cites [132] Dong, Y. et al. Plasticity of synaptic transmission in human stem cell-derived neural networks. iScience 23, 100829 (2020). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Evidence of structural defects in myelin is supported by differences in the expression of genes involved in oligodendrocyte differentiation and myelination in the brains of individuals with Down syndrome.

“Evidence of structural defects in myelin is supported by differences in the expression of genes involved in oligodendrocyte differentiation and myelination in the brains of individuals with DS39.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourceSupported

A few studies indicate that increased proportions of OLIG2-expressing progenitor cells are produced by trisomy 21 induced pluripotent stem cells differentiated in both two-dimensional and three-dimensional cultures, compared to controls.

“Nonetheless, a few studies indicate that increased proportions of OLIG2-expressing progenitor cells are produced by T21 iPSCs differentiated in both two-dimensional and three-dimensional cultures, compared to controls73,91.”

• cites [73] Klein, J. A. et al. Sonic hedgehog pathway modulation normalizes expression of Olig2 in rostrally patterned NPCs with trisomy 21. Front. Cell Neurosci. 15, 794675 (2021). sourcePartly supported

  The Results section, “Rostral Patterned tNPCs Show an Altered Response to SHH Activation” (page unavailable), reports higher proportions of OLIG2-positive progenitors in trisomic than euploid iPSC-derived cultures. The paper’s Methods describe cells grown in culture wells, but our copy does not report the claimed increase in a three-dimensional culture; the cited sentence does not specify which of its two references supports that part. (LLM, conf=0.85)

  Experimental — accuracy not yet measured
• cites [91] Xu, R. et al. OLIG2 drives abnormal neurodevelopmental phenotypes in human iPSC-based organoid and chimeric mouse models of Down syndrome. Cell Stem Cell 24, 908–926.e8 (2019). This study shows that trisomy 21 iPSCs overproduce OLIG2+ ventral forebrain neural progenitors and GABAergic neurons in organoids and in chimeric mouse brains. sourcePartly supported

  In Results, “Abnormal OLIG2 Protein Expression in DS hiPSC-Derived Ventral Forebrain Organoids” (page unavailable), the paper reports a higher proportion of OLIG2+ cells in trisomy 21 organoids than in controls. Its 2D-culture experiment, described in “Human PSC-Derived OLIG2+ Ventral Forebrain NPCs Give Rise to GABAergic Neurons” (page unavailable), examines differentiation of OLIG2+ cells but does not report a trisomy 21-versus-control comparison in 2D cultures. (LLM, conf=0.87)

  Experimental — accuracy not yet measured

When DS iPSC-derived neurons are transplanted into the mouse brain, they have reduced structural plasticity relative to controls.

“Moreover, neurons generated from iPSCs derived from individuals with DS have little to no capacity for either LTP or LTD in vitro132, and when transplanted into the mouse brain, these neurons have reduced structural plasticity relative to controls133.”

• cites [133] Real, R. et al. In vivo modeling of human neuron dynamics and Down syndrome. Science 362, eaau1810 (2018). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

DS alters the secretome of astrocytes, which exerts a direct impact on synaptogenesis.

“For example, DS has been shown to alter the secretome (the factors secreted by cells) of astrocytes, which exerts a direct impact on synaptogenesis131,144.”

• cites [131] Araujo, B. H. S. et al. Down syndrome iPSC-derived astrocytes impair neuronal synaptogenesis and the mTOR pathway in vitro. Mol. Neurobiol. 55, 5962–5975 (2018). sourceNot checked — no full text of the source
• cites [144] Caldwell, A. L. M. et al. Aberrant astrocyte protein secretion contributes to altered neuronal development in multiple models of neurodevelopmental disorders. Nat. Neurosci. 25, 1163–1178 (2022). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

The early developmental onset of network-level disruptions in DS coincides with the emergence of intellectual disability.

“The early developmental onset of these network-level disruptions — which are probably the product of altered synapse formation and function — coincides with the emergence of intellectual disability, suggesting that the cognitive deficits may be the product of impaired network-level function37,140–142.”

• cites [37] Silverman, W. Down syndrome: cognitive phenotype. Ment. Retard. Dev. Disabil. Res. Rev. 13, 228–236 (2007). sourceNot checked — no full text of the source
• cites [140] Frank, K. & Esbensen, A. J. Fine motor and self-care milestones for individuals with Down syndrome using a retrospective chart review. J. Intellect. Disabil. Res. 59, 719–729 (2015). sourceNot checked — no full text of the source
• cites [141] Esbensen, A. J. et al. Outcome measures for clinical trials in Down syndrome. Am. J. Intellect. Dev. Disabil. 122, 247–281 (2017). sourceCould not verify

  The paper’s Abstract states that Down syndrome is associated with intellectual disability, but it does not describe the developmental onset of network-level disruptions or relate their timing to the emergence of disability. Searches for network connectivity, synapse formation, and early onset found no passage addressing that relationship; the Results passages on early changes concern Alzheimer disease in adults. (LLM, conf=0.74)

  Experimental — accuracy not yet measured
• cites [142] Faught, G. G., Conners, F. A. & Himmelberger, Z. M. Auditory and visual sustained attention in Down syndrome. Res. Dev. Disabil. 53–54, 135–146 (2016). sourcePartly supported

  The Introduction (page unavailable) links cognitive abnormalities in Down syndrome to abnormal brain development and identifies Down syndrome as a cause of intellectual disability. It does not describe network-level disruptions or establish that their onset coincides with the emergence of intellectual disability. (LLM, conf=0.78)

  Experimental — accuracy not yet measured

Studies using transcriptomics and new analytical tools have suggested that neurogenesis, gliogenesis and myelination may be temporally altered in Down syndrome.

“Indeed, studies using transcriptomics and new analytical tools have suggested that neurogenesis, gliogenesis and myelination may be temporally altered in DS39,106,107.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourcePartly supported

  The Results (page unavailable) report developmental changes in genes associated with oligodendrocyte differentiation and myelination in Down syndrome, and identify altered neuronal-differentiation gene modules. The Introduction (page unavailable) reports neurogenesis defects from earlier mouse studies. This paper does not establish temporal alteration of neurogenesis and gliogenesis as broadly as the citing sentence suggests. (LLM, conf=0.82)

  Experimental — accuracy not yet measured
• cites [106] Zhou, Y., Tao, L. & Zhu, Y. TempShift reveals the sequential development of human neocortex and skewed developmental timing of Down syndrome brains. Brain Sci. 13, 1070 (2023). The authors have used TempShift — an R-based algorithm — to reveal a temporal shift of gene expression trajectories in Down syndrome cortical development. sourcePartly supported

  Results §3.5 reports delayed expression of oligodendrocyte-enriched genes, including myelin basic protein, and says other shifted genes imply delayed oligodendrocyte generation in Down syndrome. This supports possible timing changes related to gliogenesis and myelination. The Introduction mentions defects in neurogenesis, but the cited results do not establish a temporal alteration in neurogenesis; neuronal migration is a distinct process. Page numbers were not available in our copy. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [107] Reiche, L., Küry, P. & Göttle, P. Aberrant oligodendrogenesis in Down syndrome: shift in gliogenesis? Cells 8, 1591 (2019). sourceSupported

Increased astrogliogenesis can be partially reversed by silencing HSA21 by the non-coding RNA XIST in induced pluripotent stem cell-derived astrocyte progenitor cells.

“This increased astrogliogenesis can be partially reversed by the silencing of HSA21 by the non-coding RNA XIST in iPSC-derived astrocyte progenitor cells104,105.”

• cites [104] Kawatani, K. et al. A human isogenic iPSC-derived cell line panel identifies major regulators of aberrant astrocyte proliferation in Down syndrome. Commun. Biol. 4, 730 (2021). sourceSupported
• cites [105] Bansal, P. et al. A dynamic in vitro model of Down syndrome neurogenesis with trisomy 21 gene dosage correction. Sci. Adv. 10, eadj0385 (2024). sourcePartly supported

  The Results section ('T21 dosage correction early in neural differentiation rescues neurogenesis') reports that XIST-mediated trisomy 21 silencing suppresses the excess astrocyte lineage commitment, supporting the reversal claim. But the correction was initiated in iPSCs or on the first day of differentiation, before the neural progenitor cell stage; the paper does not identify the treated cells as astrocyte progenitor cells. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

In xenografts of human iPSC-derived neurons into mouse brain, T21 neurons exhibit reduced network activity relative to control neurons.

“More recently, xenografts of human iPSC-derived neurons into mouse brain revealed that, although both control neurons and T21 neurons can successfully incorporate into the mouse brain by forming synapses with the surrounding mouse neurons, T21 neurons exhibit reduced network activity relative to control neurons133.”

• cites [133] Real, R. et al. In vivo modeling of human neuron dynamics and Down syndrome. Science 362, eaau1810 (2018). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Astrocytes and microglia have a role in the DS synaptic phenotype.

“Although the tools used to ensure accurate proportions of interneuron subtypes in a culture system have only recently been developed132, simple neuron–glia co-cultures have already provided evidence that astrocytes and microglia do have a role in the DS synaptic phenotype131,134,135.”

• cites [131] Araujo, B. H. S. et al. Down syndrome iPSC-derived astrocytes impair neuronal synaptogenesis and the mTOR pathway in vitro. Mol. Neurobiol. 55, 5962–5975 (2018). sourceNot checked — no full text of the source
• cites [134] Garcia, O., Torres, M., Helguera, P., Coskun, P. & Busciglio, J. A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down’s syndrome. PLoS ONE 5, e14200 (2010). sourcePartly supported

  The Introduction and Results report that neurons co-cultured with Down syndrome astrocytes developed abnormal spines and reduced synaptic density and activity. The paper supports an astrocyte role in the DS synaptic phenotype, but our copy does not establish the claimed role for microglia. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [135] Mizuno, G. O. et al. Aberrant calcium signaling in astrocytes inhibits neuronal excitability in a human Down syndrome stem cell model. Cell Rep. 24, 355–365 (2018). sourcePartly supported

  The Results section, “DS Astroglia Promote Synaptic Connectivity,” reports that neurons co-cultured with Down syndrome astroglia had increased postsynaptic current amplitudes and synapse density, supporting an astrocyte role in the synaptic phenotype. The paper’s neuron–astroglia co-cultures do not establish the claimed role for microglia. (LLM, conf=0.87)

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Genome-wide dysregulation of gene expression in neurons likely leads to over-expression and/or under-expression of key genes that regulate synaptogenesis.

“Genome-wide dysregulation of gene expression (Box 3) in neurons likely leads to over-expression and/or under-expression of key genes that regulate synaptogenesis, but specific candidates have yet to be identified74,77,81,143.”

• cites [74] Li, Z. et al. Asynchronous excitatory neuron development in an isogenic cortical spheroid model of Down syndrome. Front. Neurosci. 16, 932384 (2022). sourcePartly supported

  The Results report up- and down-regulated genes in excitatory neurons, and the Discussion identifies BCL11B—a gene important for synapse formation—as less associated with trisomic ExN4 cells. This supports a possible link between neuronal gene dysregulation and synaptic development, but the paper does not establish that genome-wide dysregulation causes altered expression of synaptogenesis-regulating genes. (LLM, conf=0.82)

  Experimental — accuracy not yet measured
• cites [77] Tang, X. Y. et al. DSCAM/PAK1 pathway suppression reverses neurogenesis deficits in iPSC-derived cerebral organoids from patients with Down syndrome. J. Clin. Invest. 131, 135763 (2021). sourcePartly supported

  The Introduction (page unavailable) reports both upregulated and downregulated genes in Down syndrome cerebral organoids, supporting the gene-expression component. It links those changes chiefly to neurogenesis and nervous-system development, not to genes regulating synaptogenesis; it does not establish that the expression changes cause synaptogenesis deficits in neurons. (LLM, conf=0.82)

  Experimental — accuracy not yet measured
• cites [81] Weick, J. P. et al. Deficits in human trisomy 21 iPSCs and neurons. Proc. Natl Acad. Sci. USA 110, 9962–9967 (2013). sourceNot checked — no full text of the source
• cites [143] Gonzales, P. K. et al. Transcriptome analysis of genetically matched human induced pluripotent stem cells disomic or trisomic for chromosome 21. PLoS ONE 13, e0194581 (2018). sourcePartly supported

  The Results (‘Gene expression in trisomic cells’; page unavailable) report 1,377 transcripts differentially expressed between trisomic and disomic neuronal cultures, including changes in synaptic-signaling categories. They do not establish that these changes affect genes regulating synaptogenesis or lead to altered synapse formation; the paper also cautions that the neuronal cultures may not have differentiated equivalently. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

TempShift revealed several genes displaying heterochronic expression in DS, including several synaptic proteins.

“Furthermore, a recent study has applied a new algorithm, TempShift, that detects heterochronic expression of genes between species or between individuals with a disease and matched controls, and revealed several genes displaying heterochronic expression in DS, including several synaptic proteins106,152.”

• cites [106] Zhou, Y., Tao, L. & Zhu, Y. TempShift reveals the sequential development of human neocortex and skewed developmental timing of Down syndrome brains. Brain Sci. 13, 1070 (2023). The authors have used TempShift — an R-based algorithm — to reveal a temporal shift of gene expression trajectories in Down syndrome cortical development. sourceSupported
• cites [152] Zhu, Y. et al. Spatiotemporal transcriptomic divergence across human and macaque brain development. Science 362, eaat8077 (2018). sourcePartly supported

  The ‘Heterochronic changes in human and macaque brain transcriptome’ section reports using TempShift to identify heterochronic genes between species. The ‘Species difference in spatio-temporal expression of disease genes’ section identifies synaptic proteins with such differences, but describes human–macaque comparisons involving ASD-associated genes, not heterochronic expression in Down syndrome (DS) or comparisons with matched disease controls. Page numbers are unavailable in our copy. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

Inflammatory cytokine levels in post-mortem tissue from fetuses and children with DS are increased relative to age-matched controls.

“It has been shown that the levels of inflammatory cytokines in post-mortem tissue from fetuses and children with DS are increased relative to age-matched controls, suggesting that microglia may become hyperactivated in the developing DS brain147 (see also Box 4).”

• cites [147] Flores-Aguilar, L. et al. Evolution of neuroinflammation across the lifespan of individuals with Down syndrome. Brain 143, 3653–3671 (2020). sourcePartly supported

  In “Altered microglial phenotype and increased brain cytokine expression in children with Down syndrome” (page not provided), the paper reports significantly higher IL-8 and IL-10 in post-mortem frontal cortex from children with Down syndrome. The same section reports no significant difference in inflammatory markers in foetal brain homogenates versus controls. Increased cytokines in foetal cortical cell-culture media do not establish the claimed increase in post-mortem foetal tissue. (LLM, conf=0.90)

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: During neurodevelopment, microglia are largely responsible for synaptic pruning and refinement of neuronal networks, and their activity can be modulated by levels of inflammatory cytokines in their extracellular environment.

Increased inflammatory activity in the developing brain may drive microglia to excessively prune synapses and disrupt network refinement.

“However, genetic knockdown of type I IFN receptors reduces these phenotypes148, suggesting that increased inflammatory activity in the developing brain may drive microglia to excessively prune synapses and disrupt network refinement in the developing brain.”

• cites [148] Jin, M. et al. Type-I-interferon signaling drives microglial dysfunction and senescence in human iPSC models of Down syndrome and Alzheimer’s disease. Cell Stem Cell 29, 1135–1153.e8 (2022). sourcePartly supported

  The Results section (‘Inhibiting the expression of IFNARs rescues the defective DS microglia development’; page unavailable) reports that elevated pruning by Down syndrome microglia impaired neurotransmission and synaptic plasticity, and that reducing IFNAR expression partially rescued these defects. This supports the proposed link between increased type I interferon signaling and excessive pruning in the developing-brain model. The paper does not directly assess network refinement or establish the same effect for inflammatory activity generally. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: During neurodevelopment, microglia are largely responsible for synaptic pruning and refinement of neuronal networks, and their activity can be modulated by levels of inflammatory cytokines in their extracellular environment.

Introduction of exogenous THBS1 into cultures rescues synaptic and spine deficits even when neurons are co-cultured with astrocytes from individuals with DS.

“The introduction of exogenous THBS1 into these cultures rescues synaptic and spine deficits, even when neurons are co-cultured with astrocytes from individuals with DS134.”

• cites [134] Garcia, O., Torres, M., Helguera, P., Coskun, P. & Busciglio, J. A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down’s syndrome. PLoS ONE 5, e14200 (2010). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Trisomy 21 iPSCs overproduce OLIG2+ ventral forebrain neural progenitors and GABAergic neurons in organoids and in chimeric mouse brains.

“This study shows that trisomy 21 iPSCs overproduce OLIG2+ ventral forebrain neural progenitors and GABAergic neurons in organoids and in chimeric mouse brains.”

• cites [91] Xu, R. et al. OLIG2 drives abnormal neurodevelopmental phenotypes in human iPSC-based organoid and chimeric mouse models of Down syndrome. Cell Stem Cell 24, 908–926.e8 (2019). This study shows that trisomy 21 iPSCs overproduce OLIG2+ ventral forebrain neural progenitors and GABAergic neurons in organoids and in chimeric mouse brains. sourcePartly supported

  The Results report more OLIG2+ cells in Down syndrome organoids than in controls and overproduction of GABAergic neurons in chimeric mouse brains; the organoid rescue experiments also support GABAergic-neuron overproduction. But the Results on six-month-old chimeric brains say no nestin+ human neural progenitors were found there and identify the OLIG2+ donor-derived cells as likely oligodendroglial progenitors. Thus the claim is not supported if it attributes overproduction of OLIG2+ ventral forebrain neural progenitors to the mouse brains as well as the organoids (page unavailable in our copy). (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Astrocytes isolated from DS fetal brain tissue produce less THBS1 than control astrocytes.

“Astrocytes isolated from DS fetal brain tissue produce less THBS1 than control astrocytes, and rodent neurons cultured with these astrocytes have fewer synapses and abnormal spine morphology than neurons cultured with control astrocytes134.”

• cites [134] Garcia, O., Torres, M., Helguera, P., Coskun, P. & Busciglio, J. A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down’s syndrome. PLoS ONE 5, e14200 (2010). sourceSupported

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Differences in cortical development between mice and humans limit the ability of mouse models to define mechanisms relevant to the human DS phenotype.

“The field has typically relied on mouse models to gain understanding of the impact of T21, but differences in cortical development between mice and humans — including the complexity of progenitor types or the formation of a lissencephalic rather than gyrencephalic brain153–155 — limit their ability to define mechanisms relevant to the human phenotype.”

• cites [153] Vaid, S. & Huttner, W. B. Progenitor-based cell biological aspects of neocortex development and evolution. Front. Cell Dev. Biol. 10, 892922 (2022). sourcePartly supported

  Section 2 (page unavailable) describes the mouse neocortex as lissencephalic and reports differences in progenitor populations between mice and species with expanded neocortices. The paper does not address Down syndrome or state that these differences limit mouse models’ ability to define mechanisms of the human DS phenotype. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [154] Ribeiro, P. F. et al. The human cerebral cortex is neither one nor many: neuronal distribution reveals two quantitatively different zones in the gray matter, three in the white matter, and explains local variations in cortical folding. Front. Neuroanat. 7, 28 (2013). sourcePartly supported

  The Discussion section on local variations in cortical folding discusses differences in gyrification across species and developmental mechanisms of folding. It does not identify the mouse cortex as lissencephalic, compare cortical progenitor types, or assess whether mouse models can define mechanisms of the human Down syndrome phenotype. No page number is available in our copy. (LLM, conf=0.73)

  Experimental — accuracy not yet measured
• cites [155] Ventura-Antunes, L., Mota, B. & Herculano-Houzel, S. Different scaling of white matter volume, cortical connectivity, and gyrification across rodent and primate brains. Front. Neuroanat. 7, 3 (2013). sourcePartly supported

  The Discussion (page unavailable) describes mouse cortices as practically lissencephalic, and the Results and Discussion report different patterns of cortical folding in rodents and primates. The paper does not address progenitor-type complexity or establish that these differences limit mouse models’ ability to define mechanisms relevant to the human Down syndrome phenotype. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

Microglia in the frontal cortex of children with DS have increased soma size relative to controls.

“Furthermore, microglia in the frontal cortex of children with DS have increased soma size relative to controls, indicative of a distinct morphology and potential overactivation147.”

• cites [147] Flores-Aguilar, L. et al. Evolution of neuroinflammation across the lifespan of individuals with Down syndrome. Brain 143, 3653–3671 (2020). sourceSupported

• AssumptionRests on an assumption: During neurodevelopment, microglia are largely responsible for synaptic pruning and refinement of neuronal networks, and their activity can be modulated by levels of inflammatory cytokines in their extracellular environment.

Down syndrome cortical development shows a temporal shift of gene expression trajectories.

“The authors have used TempShift — an R-based algorithm — to reveal a temporal shift of gene expression trajectories in Down syndrome cortical development.”

• cites [106] Zhou, Y., Tao, L. & Zhu, Y. TempShift reveals the sequential development of human neocortex and skewed developmental timing of Down syndrome brains. Brain Sci. 13, 1070 (2023). The authors have used TempShift — an R-based algorithm — to reveal a temporal shift of gene expression trajectories in Down syndrome cortical development. sourceSupported

Astrocytes play a role in regulating neuronal function in Down syndrome pathogenesis.

“This study identifies a role for astrocytes in regulating neuronal function in Down syndrome pathogenesis using trisomy 21 iPSC-derived neurons and astrocytes in co-cultures, drug treatment and chimeric mouse brains.”

• cites [82] Chen, C. et al. Role of astroglia in Down’s syndrome revealed by patient-derived human-induced pluripotent stem cells. Nat. Commun. 5, 4430 (2014). This study identifies a role for astrocytes in regulating neuronal function in Down syndrome pathogenesis using trisomy 21 iPSC-derived neurons and astrocytes in co-cultures, drug treatment and chimeric mouse brains. sourceSupported

T21 impacts gene expression across the genome.

“However, unbiased analyses using omics technology have recently revealed that T21 impacts gene expression across the genome39,74,143,156–159.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourceSupported
• cites [74] Li, Z. et al. Asynchronous excitatory neuron development in an isogenic cortical spheroid model of Down syndrome. Front. Neurosci. 16, 932384 (2022). sourceSupported
• cites [143] Gonzales, P. K. et al. Transcriptome analysis of genetically matched human induced pluripotent stem cells disomic or trisomic for chromosome 21. PLoS ONE 13, e0194581 (2018). sourceSupported
• cites [156] Letourneau, A. et al. Domains of genome-wide gene expression dysregulation in Down’s syndrome. Nature 508, 345–350 (2014). sourceNot checked — no full text of the source
• cites [157] Martinez, J. L. et al. Transcriptional consequences of trisomy 21 on neural induction. Front. Cell Neurosci. 18, 1341141 (2024). sourceSupported
• cites [158] Vaiasicca, S. et al. Transcriptomic analysis of stem cells from chorionic villi uncovers the impact of chromosomes 2, 6 and 22 in the clinical manifestations of Down syndrome. Stem Cell Res. Ther. 14, 265 (2023). sourceSupported
• cites [159] Sullivan, K. D. et al. Trisomy 21 consistently activates the interferon response. eLife 5, e16220 (2016). sourceSupported

Gene expression analysis of cortical tissue showed robust down-regulation of LIN28B during midfetal cortical development in DS.

“Evidence for heterochrony in DS is revealed by gene expression analysis of cortical tissue that showed the robust down-regulation during midfetal cortical development of LIN28B, a gene that promotes proliferation of NPCs in a developmental, stage-specific manner and is one of the genes mutated in the original heterochronic C. elegans mutants39,150,151.”

• cites [39] Olmos-Serrano, J. L. et al. Down syndrome developmental brain transcriptome reveals defective oligodendrocyte differentiation and myelination. Neuron 89, 1208–1222 (2016). This multi-region transcriptome analysis of Down syndrome and euploid control brains spanning from mid-fetal development to adulthood identifies temporal and spatial genome-wide alterations associated with distinct biological processes. sourceCould not verify

  The Results section, “Genome-Wide Spatiotemporal Alterations of Gene Expression in DS Brains” (page unavailable), describes expression profiling of DS and control cortical tissue. However, searches for LIN28B and for midfetal down-regulation found no passage in our copy reporting the claimed LIN28B finding. (LLM, conf=0.73)

  Experimental — accuracy not yet measured
• cites [150] Ambros, V. & Horvitz, H. R. Heterochronic mutants of the nematode Caenorhabditis elegans. Science 226, 409–416 (1984). sourceNot checked — no full text of the source
• cites [151] Yang, M. et al. Lin28 promotes the proliferative capacity of neural progenitor cells in brain development. Development 142, 1616–1627 (2015). sourcePartly supported

  The section on Lin28a deletion reports that Lin28a/b protein levels decline as the mouse cerebral cortex develops. The paper does not report gene-expression analysis of midfetal cortical tissue in Down syndrome or establish robust LIN28B down-regulation in DS; its evidence concerns a different species, condition, and measurement. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

The temporal and frontal lobes, neural correlates of cognitive domains affected in Down syndrome, are smaller in individuals with Down syndrome than in healthy controls.

“The neural correlates of these cognitive domains, namely the temporal and frontal lobes, are smaller in individuals with DS than in healthy controls2–4.”

• cites [2] Becker, L., Mito, T., Takashima, S. & Onodera, K. Growth and development of the brain in Down syndrome. Prog. Clin. Biol. Res. 373, 133–152 (1991). This review summarizes the neuronal alterations (cortical lamination, reduced dendritic ramifications and diminished synapse formation) and non-neuronal alterations observed in the early postnatal Down syndrome brain and relates them to intellectual disability.Not checked — no full text of the source
• cites [3] Coyle, J. T., Oster-Granite, M. L. & Gearhart, J. D. The neurobiologic consequences of Down syndrome. Brain Res. Bull. 16, 773–787 (1986). sourceNot checked — no full text of the source
• cites [4] Wisniewski, K. E. Down syndrome children often have brain with maturation delay, retardation of growth, and cortical dysgenesis. Am. J. Med. Genet. Suppl. 7, 274–281 (1990).Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

During fetal and early postnatal stages, the brains of individuals with Down syndrome exhibit altered cytoarchitecture, including disrupted cortical lamination and reductions in the numbers of specific cortical cell types.

“Moreover, during fetal and early postnatal stages, the brains of individuals with DS exhibit altered cytoarchitecture, including disrupted cortical lamination and reductions in the numbers of specific cortical cell types (Fig. 1).”

It is not possible to generate mice harbouring three copies of every gene on human chromosome 21 while maintaining human-like gene regulation because the genes on HSA21 are localized on at least three different murine chromosomes.

“Although mouse models of DS have been generated, it is not possible to generate mice harbouring three copies of every gene on human chromosome 21 (HSA21) while maintaining human-like gene regulation because the genes on HSA21 are localized on at least three different murine chromosomes.”

Down syndrome is caused by trisomy 21.

“Down syndrome (DS), caused by trisomy 21 (T21), is the most common genetic cause of intellectual disability1.”

• cites [1] Quinonez, S. C. & Barsh, G. in Pathophysiology of Disease: An Introduction to Clinical Medicine (eds Hammer, G. D. & McPhee, S. J.) Ch. 2 (McGraw-Hill Education, 2019).Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The early emergence of structural deficits in the brains of individuals with Down syndrome implies disruptions to early neurodevelopment.

“The early emergence of structural deficits in the brains of individuals with DS implies disruptions to early neurodevelopment, but the exact processes that are affected and the cellular and molecular mechanisms that drive these phenotypes are unknown.”

• AssumptionRests on an assumption: The exact processes affected and the cellular and molecular mechanisms that drive the phenotypes in Down syndrome are unknown.

Astrocyte number, usually measured by immunostaining for glial fibrillary acidic protein, is often assessed relative to the number of neurons, which means that an increase could reflect decreased numbers of neurons or increased numbers of astrocytes.

“However, astrocyte number, usually measured by immunostaining for glial fibrillary acidic protein (GFAP), is often assessed relative to the number of neurons, which means that this increase could reflect decreased numbers of neurons or increased numbers of astrocytes42.”

• cites [42] Guidi, S. et al. Neurogenesis impairment and increased cell death reduce total neuron number in the hippocampal region of fetuses with Down syndrome. Brain Pathol. 18, 180–197 (2008). sourceNot checked — no full text of the source

Discrepancies in interneuron findings may be owing to variations in induced pluripotent stem cell modelling methodology, including different differentiation strategies, the use of different cell lines, or complexities in mimicking the development of interneurons.

“These discrepancies may be owing to variations in iPSC modelling methodology, including different differentiation strategies, the use of different cell lines, or complexities in mimicking the development of interneurons.”

The cortex is not uniformly affected by trisomy 21.

“Here, we review the impact of T21 as it pertains to human neocortical development, but it is important to appreciate that the cortex is not uniformly affected by T21.”

These structural differences correlate with functional deficits in expressive language and working memory regulated by these regions.

“These structural differences correlate with functional deficits in expressive language and working memory regulated by these regions36,37.”

• cites [36] Chapman, R. S. & Hesketh, L. J. Behavioral phenotype of individuals with Down syndrome. Ment. Retard. Dev. Disabil. Res. Rev. 6, 84–95 (2000). sourceNot checked — no full text of the source
• cites [37] Silverman, W. Down syndrome: cognitive phenotype. Ment. Retard. Dev. Disabil. Res. Rev. 13, 228–236 (2007). sourceNot checked — no full text of the source

Regional differences in the structure of the cortex in Down syndrome suggest that not all regions, and therefore not all spatially defined progenitors, are similarly affected.

“Furthermore, regional differences in the structure of the cortex in DS suggest that not all regions, and therefore not all spatially defined progenitors, are similarly affected.”

Neural progenitor cells derived from the fetal brain of individuals with Down syndrome generate more astrocytes in culture than control fetal neural progenitor cells.

“That there is increased gliogenesis in DS is supported by reports that NPCs derived from the fetal brain of individuals with DS generate more astrocytes in culture than in control fetal NPCs99,101,102.”

• cites [99] Zdaniuk, G., Wierzba-Bobrowicz, T., Szpak, G. M. & Stepien, T. Astroglia disturbances during development of the central nervous system in fetuses with Down’s syndrome. Folia Neuropathol. 49, 109–114 (2011).Not checked — no full text of the source
• cites [101] Mito, T. & Becker, L. E. Developmental changes of S-100 protein and glial fibrillary acidic protein in the brain in Down syndrome. Exp. Neurol. 120, 170–176 (1993). sourceNot checked — no full text of the source
• cites [102] Bahn, S. et al. Neuronal target genes of the neuron-restrictive silencer factor in neurospheres derived from fetuses with Down’s syndrome: a gene expression study. Lancet 359, 310–315 (2002). sourceNot checked — no full text of the source

Experimental design is crucial in induced pluripotent stem cell modelling.

“These results indicate that experimental design is crucial in iPSC modelling.”

These differences are present across the cortical laminae.

“These differences are present across the cortical laminae115–118.”

• cites [115] Marin-Padilla, M. Structural abnormalities of the cerebral cortex in human chromosomal aberrations: a Golgi study. Brain Res. 44, 625–629 (1972). sourceNot checked — no full text of the source
• cites [116] Marin-Padilla, M. Pyramidal cell abnormalities in the motor cortex of a child with Down’s syndrome. A Golgi study. J. Comp. Neurol. 167, 63–81 (1976). sourceNot checked — no full text of the source
• cites [117] Takashima, S., Becker, L. E., Armstrong, D. L. & Chan, F. Abnormal neuronal development in the visual cortex of the human fetus and infant with Down’s syndrome. A quantitative and qualitative Golgi study. Brain Res. 225, 1–21 (1985). This Golgi analysis of DS fetal and infant brains shows the same neuronal morphology and spine counts as those of control fetuses; however, DS brains had shorter basilar dendrites and decreased numbers of spines with altered morphology and defective cortical layering. sourceNot checked — no full text of the source
• cites [118] Takashima, S., Iida, K., Mito, T. & Arima, M. Dendritic and histochemical development and ageing in patients with Down’s syndrome. J. Intellect. Disabil. Res. 38, 265–273 (1994). sourceNot checked — no full text of the source

Synapse development is disrupted in DS.

“These findings provide compelling evidence that synapse development is disrupted in DS, but the exact molecular and biochemical drivers of this disruption remain unclear.”

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Neurons from both the motor and visual cortices of infants with Down syndrome as young as 2 months of age have fewer dendritic spines.

“Specifically, neurons from both the motor and visual cortices of infants with DS as young as 2 months of age have fewer dendritic spines117,118.”

• cites [117] Takashima, S., Becker, L. E., Armstrong, D. L. & Chan, F. Abnormal neuronal development in the visual cortex of the human fetus and infant with Down’s syndrome. A quantitative and qualitative Golgi study. Brain Res. 225, 1–21 (1985). This Golgi analysis of DS fetal and infant brains shows the same neuronal morphology and spine counts as those of control fetuses; however, DS brains had shorter basilar dendrites and decreased numbers of spines with altered morphology and defective cortical layering. sourceNot checked — no full text of the source
• cites [118] Takashima, S., Iida, K., Mito, T. & Arima, M. Dendritic and histochemical development and ageing in patients with Down’s syndrome. J. Intellect. Disabil. Res. 38, 265–273 (1994). sourceNot checked — no full text of the source

In children with DS, oscillatory networks involved in memory consolidation are disrupted within the first postnatal months.

“Network-level functional analyses of infants and toddlers with DS are scarce, but evidence from early EEG studies suggests that oscillatory networks involved in memory consolidation are disrupted within the first postnatal months in children with DS136–138.”

• cites [136] Hamaguchi, H., Hashimoto, T., Mori, K. & Tayama, M. Sleep in the Down syndrome. Brain Dev. 11, 399–406 (1989). sourceNot checked — no full text of the source
• cites [137] McAlaster, R. Postnatal cerebral maturation in Down’s syndrome children: a developmental EEG coherence study. Int. J. Neurosci. 65, 221–237 (1992). sourceNot checked — no full text of the source
• cites [138] Schmid, R. G. & Sadowsky, K. Z-Transformed EEG power spectra of children with Down syndrome vs a control group. Neuropediatrics 16, 218–224 (1985). sourceNot checked — no full text of the source

iPSC-based systems do not fully recapitulate the complexity of circuits and microcircuits that exist within the brain.

“Importantly, iPSC-based systems do not fully recapitulate the complexity of circuits and microcircuits that exist within the brain (Box 1).”

• cites Box 1Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Children with DS as young as 6 months of age show significantly reduced alpha power, implicated in working memory, relative to age-matched controls.

“For example, children as young as 6 months of age show significantly reduced alpha power, implicated in working memory, relative to age-matched controls138.”

• cites [138] Schmid, R. G. & Sadowsky, K. Z-Transformed EEG power spectra of children with Down syndrome vs a control group. Neuropediatrics 16, 218–224 (1985). sourceNot checked — no full text of the source

The spines that are present in Down syndrome exhibit morphological anomalies, such as abnormally small and exceptionally long, thin spines.

“Moreover, the spines that are present exhibit morphological anomalies, such as abnormally small and exceptionally long, thin spines115–118 (Fig. 3a).”

• cites [115] Marin-Padilla, M. Structural abnormalities of the cerebral cortex in human chromosomal aberrations: a Golgi study. Brain Res. 44, 625–629 (1972). sourceNot checked — no full text of the source
• cites [116] Marin-Padilla, M. Pyramidal cell abnormalities in the motor cortex of a child with Down’s syndrome. A Golgi study. J. Comp. Neurol. 167, 63–81 (1976). sourceNot checked — no full text of the source
• cites [117] Takashima, S., Becker, L. E., Armstrong, D. L. & Chan, F. Abnormal neuronal development in the visual cortex of the human fetus and infant with Down’s syndrome. A quantitative and qualitative Golgi study. Brain Res. 225, 1–21 (1985). This Golgi analysis of DS fetal and infant brains shows the same neuronal morphology and spine counts as those of control fetuses; however, DS brains had shorter basilar dendrites and decreased numbers of spines with altered morphology and defective cortical layering. sourceNot checked — no full text of the source
• cites [118] Takashima, S., Iida, K., Mito, T. & Arima, M. Dendritic and histochemical development and ageing in patients with Down’s syndrome. J. Intellect. Disabil. Res. 38, 265–273 (1994). sourceNot checked — no full text of the source

Studies examining excitation and inhibition in iPSC-derived neurons have to date only utilized GABA as a marker for inhibitory neurons.

“For example, studies examining excitation and inhibition in iPSC-derived neurons have, to date, only utilized GABA as a marker for inhibitory neurons, so it is unclear if the proportion of specific interneuron subtypes in these cultures accurately reflects the populations that are present in vivo.”

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Studies examining excitation and inhibition in iPSC-derived neurons have only examined cultures containing neurons in the absence of glia.

“Additionally, these studies have only examined cultures containing neurons (both inhibitory and excitatory) in the absence of glia, so it is possible that the imbalanced inhibitory–excitatory synaptic transmission observed in the mouse models is not intrinsic to T21 neurons and requires non-neuronal cell types.”

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Deficient synaptogenesis and synaptic function are thought to be key drivers of intellectual disability in Down syndrome.

“Deficient synaptogenesis and synaptic function are thought to be key drivers of intellectual disability in DS111 (Fig. 3).”

• cites [111] Garner, C. C. & Wetmore, D. Z. Synaptic pathology of Down syndrome. Adv. Exp. Med. Biol. 970, 451–468 (2012). sourceNot checked — no full text of the source

In T21 iPSC-derived neurons, the proportion of inhibitory to excitatory synaptic transmission does not differ from controls, contrary to findings in mouse models of DS.

“However, the proportion of inhibitory to excitatory synaptic transmission, as assessed by the number of inhibitory post-synaptic currents relative to the number of excitatory post-synaptic currents detected using whole-cell voltage clamp, does not differ between control and T21 iPSC-derived neurons, contrary to findings in mouse models of DS81.”

• cites [81] Weick, J. P. et al. Deficits in human trisomy 21 iPSCs and neurons. Proc. Natl Acad. Sci. USA 110, 9962–9967 (2013). sourceNot checked — no full text of the source

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

These data suggest that astrogliogenesis may be enhanced by increased proliferation of progenitors.

“Together, these data suggest that astrogliogenesis may be enhanced by increased proliferation of progenitors.”

Trisomy 21 iPSCs show accelerated neural differentiation that correlates with disruption of intracellular redox state and its associated signaling.

“This study of trisomy 21 iPSCs reveals accelerated neural differentiation that correlates with disruption of intracellular redox state and its associated signaling.”

• cites [76] Prutton, K. M. et al. Oxidative stress as a candidate mechanism for accelerated neuroectodermal differentiation due to trisomy 21. Free Radic. Biol. Med. 186, 32–42 (2022).This study of trisomy 21 iPSCs reveals accelerated neural differentiation that correlates with disruption of intracellular redox state and its associated signalling. sourceNot checked — no full text of the source

Intellectual disability in DS has been linked to gross morphological changes in specific brain regions, which are readily apparent at fetal and early postnatal developmental stages.

“Intellectual disability in DS has been linked to gross morphological changes in specific brain regions, which are readily apparent at fetal and early postnatal developmental stages.”

Neonatal DS brain tissue has a higher percentage of primitive synaptic contacts than control tissue.

“Through electron microscopy of neonatal DS and control brains, this study reveals a higher percentage of primitive synaptic contacts in the DS tissue.”

• cites [119] Petit, T. L., LeBoutillier, J. C., Alfano, D. P. & Becker, L. E. Synaptic development in the human fetus: a morphometric analysis of normal and Down’s syndrome neocortex. Exp. Neurol. 83, 13–23 (1983). Through electron microscopy of neonatal DS and control brains, this study reveals a higher percentage of primitive synaptic contacts in the DS tissue. sourceNot checked — no full text of the source

Neuroanatomical deficits in DS are caused by cellular and molecular changes that disrupt the emergent functional properties of the brain and manifest as cognitive disability.

“These neuroanatomical deficits are caused by cellular and molecular changes that disrupt the emergent functional properties of the brain and manifest as cognitive disability (Figs. 1 and 2).”

• cites Figs. 1 and 2Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Neurodevelopment in DS tends to be impacted by a combination of all the factors mentioned in the review and others not described.

“The mechanistic consequences of T21 outlined in this Review are not mutually exclusive, and neurodevelopment in DS tends to be impacted by a combination of all the factors mentioned here and others we have not described.”

The various hypothesized mechanisms of T21 neurodevelopmental impact may exacerbate or perpetuate one another.

“The dynamic nature of developmental timing, gene regulation and cell–cell interactions in cortical development means that the various hypothesized mechanisms may exacerbate or perpetuate one another.”

The processes underlying DS neuroanatomical deficits largely occur prenatally.

“These processes largely occur prenatally and analyses of post-mortem fetal brain tissue are, thus, invaluable in providing a reference for the emerging structural and cellular differences in DS.”

Several differences in brain development in DS that seem contradictory could be driven by altered timing of intrinsically controlled events during neurogenesis, gliogenesis and synaptogenesis.

“Several of the differences in brain development in DS that have been observed and that seem to be contradictory — such as the evidence for increased numbers of glial cells but reductions in neuron populations — could be driven by altered timing of intrinsically controlled events during neurogenesis, gliogenesis and synaptogenesis (Fig. 2).”

The impact of astrocytes on synapse and neuronal network formation is probably driven in part by their capacity to support the proper electrophysiological function of individual neurons.

“The impact of astrocytes, therefore, is probably driven in part by their capacity to support the proper electrophysiological function of individual neurons, which has downstream effects on the formation of synapses and neuronal networks.”

• AssumptionRests on an assumption: Human iPSC-derived neurons provide a model system capable of electrophysiological studies with sufficient power to investigate how DS alters neurotransmission.

Limited access to fetal brain tissue impedes identification of the mechanisms that lead to differences in brain structure and intellectual disability in DS.

“However, the limited access to tissue during this period impedes identification of the mechanisms that lead to the differences in brain structure and, ultimately, to intellectual disability.”