HC atrophy is common, albeit not always present, in the preclinical course of AD (Reitz et al., 2011; Tondelli et al., 2011; Lindberg et al., 2012) and the APOE ε 4 allele has been shown to influence HC atrophy in prodromal AD (Jack et al., 2012). The gene discussed is APOE; the disease is Alzheimer disease.