Genetically, apolipoprotein E (APOE) ε4 allele status alters PCA risk but with a smaller effect than for typical Alzheimer’s disease (Schott et al., 2006; Snowden et al., 2007) and an exploratory genome-wide association study has identified three candidate genetic risk factors that may be specific to PCA (Schott et al., 2016). The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.