When the influence of fertility and ApoE genotypes on AD onset age were analyzed, parity was found to be associated with a significantly lower AD onset age (73.8 ± 6.2 years) than nulliparity (80.7 ± 5.0 years; p = 0.0007) among subjects carrying ApoE3/ApoE3 and ApoE3/ApoE2 genotypes. This evidence concerns the gene APOE and Alzheimer disease.