Cited by 356Epilepsy research and treatmentTuberous Sclerosis Complex ResearchGenetics and Neurodevelopmental Disorders

Dissecting the genetic basis of focal cortical dysplasia: a large cohort study

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Baldassari, Sara, Ribierre, Théo, Marsan, Elise, Adle-Biassette, Homa, Ferrand-Sorbets, Sarah, Bulteau, Christine, Dorison, Nathalie, Fohlen, Martine +5 more·2019·Acta Neuropathologica

Abstract

Genetic malformations of cortical development (MCDs), such as mild MCDs (mMCD), focal cortical dysplasia (FCD), and hemimegalencephaly (HME), are major causes of severe pediatric refractory epilepsies subjected to neurosurgery. FCD2 are characterized by neuropathological hallmarks that include enlarged dysmorphic neurons (DNs) and balloon cells (BCs). Here, we provide a comprehensive assessment of the contribution of germline and somatic variants in a large cohort of surgical MCD cases. We enrolled in a monocentric study 80 children with drug-resistant epilepsy and a postsurgical neuropathological diagnosis of mMCD, FCD1, FCD2, or HME. We performed targeted gene sequencing ( ≥ 2000X read depth) on matched blood-brain samples to search for low-allele frequency variants in mTOR pathway and FCD genes. We were able to elucidate 29% of mMCD/FCD1 patients and 63% of FCD2/HME patients. Somatic loss-of-function variants in the N-glycosylation pathway-associated SLC35A2 gene were found in mMCD/FCD1 cases. Somatic gain-of-function variants in MTOR and its activators (AKT3, PIK3CA, RHEB), as well as germline, somatic and two-hit loss-of-function variants in its repressors (DEPDC5, TSC1, TSC2) were found exclusively in FCD2/HME cases. We show that panel-negative FCD2 cases display strong pS6-immunostaining, stressing that all FCD2 are mTORopathies. Analysis of microdissected cells demonstrated that DNs and BCs carry the pathogenic variants. We further observed a correlation between the density of pathological cells and the variant-detection likelihood. Single-cell microdissection followed by sequencing of enriched pools of DNs unveiled a somatic second-hit loss-of-heterozygosity in a DEPDC5 germline case. In conclusion, this study indicates that mMCD/FCD1 and FCD2/HME are two distinct genetic entities: while all FCD2/HME are mosaic mTORopathies, mMCD/FCD1 are not caused by mTOR-pathway-hyperactivating variants, and ~ 30% of the cases are related to glycosylation defects. We provide a framework for efficient genetic testing in FCD/HME, linking neuropathology to genetic findings and emphasizing the usefulness of molecular evaluation in the pediatric epileptic neurosurgical population.

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  • Somatic mutations in mTOR pathway regulators are often found in focal cortical dysplasia type II.

    “In addition, somatic mutations in mTOR pathway regulators are often found in focal cortical dysplasia type II, which has overlapping histological and clinical features with TSC24,25.”

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  1. [31]Mirzaa GM Campbell CD Solovieff N Goold C Jansen LA Menon S Association of MTOR mutations with developmental brain disorders, including megalencephaly, focal cortical dysplasia, and pigmentary mosaicism JAMA Neurol 2016 73 836 845 27159400 PMC4979321

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Authors
Baldassari, S., Ribierre, T., Marsan, E., Adle-Biassette, H., Ferrand-Sorbets, S., Bulteau, C., Dorison, N., Fohlen, M., Polivka, M., Weckhuysen, S., Dorfmüller, G., Chipaux, M., & Baulac, S.
Affiliations
  • Centre National de la Recherche Scientifique (FR)
  • Hôpital Rothschild (FR)
  • Hôpital Lariboisière (FR)
Corresponding author
Baulac, Stéphanie
Venue
Acta Neuropathologica
Published
2019-08-23
Volume
138
Issue
6
Pages
885-900
ISSN
  • 0001-6322 (ISSN-L)
  • 1432-0533
OpenAlex
W2969667716
Cited by
356
References
48
Citations by year
2026: 29 · 2025: 49 · 2024: 69 · 2023: 61 · 2022: 48 · 2021: 62 · 2020: 33 · 2019: 3 · 2018: 1
FWCI
29.08
Type
journal article
Language
en
Open access
Locations
  • Acta Neuropathologica (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • HAL (submittedVersion, other-oa)
Funders
European Research Council (No682345)
Topics
  • Health Sciences › Medicine › Psychiatry and Mental health › Epilepsy research and treatment
  • Health Sciences › Medicine › Physiology › Tuberous Sclerosis Complex Research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Genetics and Neurodevelopmental Disorders
Keywords
focal cortical dysplasia, hemimegalencephaly, drug-resistant epilepsy, mTOR signaling, mTORopathies, SLC35A2, N-glycosylation defects, DEPDC5, TSC1, TSC2, loss-of-function mutations, balloon cells, dysmorphic neurons, genetic testing, pS6
MeSH terms
Adolescent, Brain, Child, Child, Preschool, Epilepsy, Female, Humans, Infant, Male, Mutation, Neurons, Cohort Studies, Malformations of Cortical Development, Hemimegalencephaly

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