After the APOE-ε4 allele was established as a risk factor for AD, some investigators looked more closely at it as a possible risk factor for other neuropsychiatric disorders including late-onset depression (Martorell et al., 2001; Oliveri et al., 1999a, 1999b; Thibaut et al., 1998). The gene discussed is APOE; the disease is Alzheimer disease.