APOE and Alzheimer disease: The ε4 allele of APOE (APOE4) is associated with anincreased risk of developing AD and a younger age of onset, at 65.1,with a narrow 95% prediction interval.95 Individuals who inherit one copy of the APOE ε4 allele havean increased risk, while those who inherit two copies (homozygous)have an even higher risk, estimated to be 8 to 12 times greater thanthose with no ε4 alleles.84,96 Recent study has concludedthat APOE4 homozygotes represent in fact a distinct genetic form ofAD.95,97