It is crucial to note that our findings are contingent upon detectable genotype differences in our sample which may be limited in the older age range. Although the UKB neuroimaging cohort features a large number of ε4/ε4 carriers (N = 869), we observe a decreasing proportion of ε4 carriers with advancing age (Figure S2A). This trend aligns with previous studies reporting lower ε4 frequencies with increasing age, partially due to earlier mortality and lower survival rates. 28 These dynamics impact our ability to accurately capture the effects of the ε4 allele in the older age groups, particularly those over age 70.
