Polygenic score modifies risk for Alzheimer’s disease in APOE ε4 homozygotes at phenotypic extremes

Author(s): Huq, AJ; Fulton-Howard, B; Riaz, M; Laws, S; Sebra, R; Ryan, J; Alzheimer's Disease Genetics Consortium; Renton, AE; Goate, AM; Masters, CL; Storey, E; Shah, RC; Murray, A; McNeil, J; Winship, I; James, PA; Lacaze, P;
Year: 2021;  
Journal: Alzheimer's & Dementia (Amsterdam, Netherlands);  
Volume: 13;  
Issue: 1;  

INTRODUCTION: Diversity in cognition among apolipoprotein E (APOE) ε4 homozygotes can range from early-onset Alzheimer’s disease (AD) to a lifetime with no symptoms.
METHODS: We evaluated a phenotypic extreme polygenic risk score (PRS) for AD between cognitively healthy APOE ε4 homozygotes aged ≥75 years (n = 213) and early-onset APOE ε4 homozygote AD cases aged ≤65 years (n = 223) as an explanation for this diversity.
RESULTS: The PRS for AD was significantly higher in APOE ε4 homozygote AD cases compared to older cognitively healthy APOE ε4/ε4 controls (odds ratio [OR] 8.39; confidence interval [CI] 2.0-35.2; P = .003). The difference in the same PRS between APOE ε3/ε3 extremes was not as significant (OR 3.13; CI 0.98-9.92; P = .053) despite similar numbers and power. There was no statistical difference in an educational attainment PRS between these age extreme case-controls.
DISCUSSION: A PRS for AD contributes to modified cognitive expression of the APOE ε4/ε4 genotype at phenotypic extremes of risk.