APOE and early-onset autosomal dominant Alzheimer disease: Given the important role of APOE variants in late-onset Alzheimer's disease, we first looked at the APOE ε4 allele as defined by the ancestral alleles rs429358-C and rs7412-C (130Arg and 176Arg) and APOE ε2 allele as defined by rs429358-T and rs7412-T (130Cys and 176Cys).