Autosomal dominant inheritance of AD is linked to mutations in genes encoding APP and presenilins 1 and 2 (Goate et al. 1991; Levy-Lahad et al. 1995; Rogaev et al. 1995; Sherrington et al. 1995) and result in increased Aβ generation, indicating its central pathogenic role in AD. The gene discussed is PSEN1; the disease is Alzheimer disease.