eLife Assessment
This valuable study assesses epigenetic clocks across ancestries, including in the context of accelerated aging in Alzheimer's Disease patients. It provides convincing evidence for population differences in age estimation accuracy across a variety of epigenetic clocks, but the degree to which these differences reflect continuous variation in ancestry, and/or are confounded by environmental or power differences is not entirely clear; consequently, the evidence that reduced portability is rooted in genetics is incomplete. Given the accelerating use of epigenetic clocks across fields, this study is nevertheless likely to be of interest to researchers working on human genetic and epigenetic variation or who apply epigenetic clocks to diverse human populations.