APOE and Polygenic Risk Shape Alzheimer Disease Onset in Extra-APP-Copy Carriers

A study published in Alzheimer's & Dementia found that common Alzheimer disease (AD) risk variants, including APOE and a broader polygenic risk score, significantly modify age at onset (AAO) in people with an extra copy of the amyloid precursor protein (APP) gene, a group that includes both autosomal dominant APP duplication (APPdup) carriers and individuals with Down syndrome (DS). The authors described it as the first study to demonstrate robust effects of both APOE and a polygenic AD risk score in APPdup carriers, and the largest genetic modifier study conducted in people with an extra APP copy.¹

The analysis combined 100 APPdup carriers and 957 individuals with DS across multiple European and US cohorts. Mean AAO was earlier in APPdup carriers than in those with DS (50.7 vs 53.3 years; P = .0005), though the authors attributed most of this gap to differences in how onset was defined across cohorts rather than a true biological difference, noting that variability in onset was similar between the two groups.

Across the combined cohort, APOE ε2 delayed AD onset (hazard ratio [HR], 0.47; P < .0001), while APOE ε4 accelerated it (HR, 1.5; P = .0003). A broader AD genetic risk score (AD-GRS), built from 77 genome-wide significant variants and excluding APOE, was independently associated with earlier onset as well (HR, 1.3 per standard deviation; P < .0001), with no interaction detected between APOE and the AD-GRS. These effects held in both APPdup and DS when analyzed separately, though the APOE ε4 effect did not reach statistical significance in the smaller APPdup group alone.

Combining APOE genotype and AD-GRS, predicted median AAO differed by roughly 9 to 10 years between individuals at the lowest versus highest genetic risk, ranging from 49.4 to 58.8 years in APPdup carriers and 50.1 to 60.1 years in individuals with DS. The authors noted this shift, while smaller than the roughly 20-year spread seen across genetic risk extremes in sporadic AD, is substantial given that AD onset in people with an extra APP copy occurs within a narrower window overall (roughly ages 40 to 60) compared with sporadic AD (roughly ages 60 to 100).¹

"Our findings suggest that incorporating the APOE genotype and AD-GRS could improve prediction of AAO in these individuals," the study authors, led by Joan Groeneveld and senior author Sven J. van der Lee, PhD, of Amsterdam UMC, wrote, adding that because these genetic factors likely act through specific biological pathways, they may also influence individual response to future pathway-targeted treatments.¹

Breaking the polygenic score into pathway-specific components, the authors found that variants related to amyloid-beta metabolism (HR, 1.2; q = .013) and angiogenesis (HR, 1.1; q = .034) were most strongly associated with AAO in the combined cohort, while variants related to endocytosis reached significance in DS specifically (HR, 1.2; q = .034) but not in APPdup. Variants related to immune response and cholesterol/lipid metabolism, both established contributors to sporadic AD risk, did not significantly modify onset in this population.

Separately, in a subset of APPdup carriers, neither the length of the APP duplication nor duplication of any of 23 individual genes on chromosome 21 was associated with AAO, suggesting the extra genetic material itself, beyond APP, does not substantially drive onset timing in that group.

REFERENCES
1. Groeneveld J, Perlaza D, Olivé C, et al. APOE and genetic risk variants influence Alzheimer's disease onset in carriers of an extra copy of APP, with and without Down syndrome. Alzheimers Dement. 2026;22:e71738. doi:10.1002/alz.71738