Although not all individuals possessing the APOE ε4 allele go on to develop AD, the probability that a randomly selected individual with the ε4/ε4 or ε3/ε4 genotype will develop AD by age 85 is estimated to be 51–60% and 23–30%, respectively (Genin et al., 2011). The gene discussed is APOE; the disease is Alzheimer disease.