Carrying one APOE ɛ4 allele (heterozygous) has been shown to increase the risk of developing AD by approximately 2–3 fold compared to carriers of two APOE ɛ3 alleles, while carrying two APOE ɛ4 alleles (homozygous) has been shown to increase the risk by almost 15 fold2,3. The gene discussed is APOE; the disease is Alzheimer disease.