APOE and Alzheimer disease: In humans, APOE presents as three allelic variants (APOE ε2, APOE ε3 and APOE ε4) and compared to individuals with the APOE ε3/ε3 genotype, the APOE ε3/ε4 genotype confers around a threefold increase in risk of developing AD and is significantly overrepresented in individuals with sAD [71, 72].