Clonal Hematopoiesis Mutations Increase Risk of Alzheimer’s Disease with APOE ε3/ε3 Genotype

Studies incorporating ultra-deep sequencing that capture very small clones may identify biologically distinct populations, potentially diluting associations or introducing heterogeneity when clones with low VAF and uncertain functional relevance are included.

“In contrast, studies incorporating ultra-deep sequencing approaches that capture very small clones may identify biologically distinct populations, potentially diluting associations or introducing heterogeneity when clones with low VAF and uncertain functional relevance are included [13].”

Smaller biomarker-focused cohorts and genotype-stratified sequencing projects report either neutral effects or an increased risk of AD pathology.

“smaller, biomarker-focused cohorts (n < 100) and specific genotype-stratified sequencing projects (n ≈ 30,000) indicate a different trajectory, reporting either neutral effects or an increased risk of AD pathology [12,13].”

Choi et al. reported an increased incidence of CHIP in AD cases compared with controls (n = 289), with effects driven specifically by APOE ε3/ε3 individuals.

“Choi et al. reported an increased incidence of CHIP in AD cases compared with controls (n = 289), with effects driven specifically by APOE ε3/ε3 individuals [13].”

Mechanistic insights provide a plausible biological framework for the heterogeneous and sometimes contradictory epidemiological findings observed across studies, particularly those derived from shared cohorts such as the ADSP.

“These mechanistic insights provide a plausible biological framework for the heterogeneous and sometimes contradictory epidemiological findings observed across studies, particularly those derived from shared cohorts such as the ADSP [10,13,34].”

The impact of clonal hematopoiesis on AD risk is strongly dependent on the identity of the driver gene and host genetic context.

“Accumulating evidence indicates that the impact of clonal hematopoiesis on AD risk is strongly dependent on the identity of the driver gene and host genetic context [10,13].”

Inferred CHIP-AD associations are strongly shaped by methodological choices, including CHIP definition (VAF 2% vs. 8%) and cohort stratification based on APOE genotype.

“This suggests that inferred CHIP-AD associations are strongly shaped by methodological choices, including CHIP definition (VAF 2% vs. 8%) and cohort stratification based on APOE genotype.”

Three independent analytical frameworks have been applied to the same ADSP cohort, yielding disparate results.

“Notably, three independent analytical frameworks have now been applied to the same ADSP cohort, yielding disparate results.”

Gene-specific effects, clonal burden, host genetic background, and neurovascular integrity all shape whether CHIP-derived immune cells exert protective or pathogenic influences in the aging brain.

“Gene-specific effects, clonal burden, host genetic background, and neurovascular integrity all shape whether CHIP-derived immune cells exert protective or pathogenic influences in the aging brain [10,11,13,19,33,34].”

Both Bouzid et al. and Choi et al. relied on the ADSP as a validation cohort yet arrived at strikingly opposed conclusions, underscoring the sensitivity of inferred CHIP effects to methodological heterogeneity.

“Notably, both studies relied on the ADSP as a validation cohort yet arrived at strikingly opposed conclusions, underscoring the sensitivity of inferred CHIP effects to methodological heterogeneity.”

The net effect of CHIP on Alzheimer's disease risk is determined by the balance between protective neuroimmune modulation and deleterious vascular and inflammatory influences, shaped by mutation type, clonal burden, disease stage, and host genetic background, including the APOE genotype.

“The net effect of CHIP on Alzheimer’s disease risk is, therefore, determined by the balance between protective neuroimmune modulation and deleterious vascular and inflammatory influences, shaped by mutation type, clonal burden, disease stage, and host genetic background, including the APOE genotype [10,13].”

A more recent study utilizing deep panel sequencing revealed an increased burden of CHIP variants in Alzheimer's disease blood samples compared to age-matched controls, primarily driven by low-VAF variants, and this increase was independently confirmed in whole-genome sequencing of ~30,000 cases and controls.

“A more recent study utilizing deep panel sequencing revealed an increased burden of CHIP variants in AD blood samples compared to age-matched controls, primarily driven by low-VAF variants26, and this AD-related increase of CHIP variants was independently confirmed in whole-genome sequencing (WGS) of ~30,000 cases and controls26.”

Large CHIP clones in the ADSP cohort have been associated with reduced AD risk and attenuated neuropathology, while smaller clones, mosaic chromosomal alterations, and specific genetic contexts may have increased susceptibility.

“While large CHIP clones in the ADSP cohort have been associated with a reduced AD risk and attenuated neuropathology [10], smaller clones, mosaic chromosomal alterations [34], and specific genetic contexts, most notably APOE stratification, may have increased susceptibility [13].”

Multiple epidemiological studies have identified the Apolipoprotein E genotype, particularly APOE ε3/ε3 alleles, as a key modifier of CHIP-associated AD risk.

“Multiple epidemiological studies have identified the Apolipoprotein E genotype, particularly APOE ε3/ε3 alleles, as a key modifier of CHIP-associated AD risk [10,13].”

Several studies report that the CHIP-associated risk of AD differs substantially by APOE genotype, with effects appearing most pronounced in individuals with APOE ε3/ε3.

“Several studies report that the CHIP-associated risk of AD differs substantially by APOE genotype, with effects appearing most pronounced in individuals with APOE ε3/ε3 [10,13].”