APOE and Alzheimer disease: One structural variant of note is the ‘translocase of outer mitochondrial membrane 40’ (TOMM40) polymorphic T-tract length (rs10524523, ‘523’); an intronic variant known to improve precision when estimating the age of onset of Alzheimer’s disease (AD) in APOE ε3 carriers and to be associated with changes in cognition in non-pathological ageing16–22.