About 1% of AD cases develop as a result of mutations within APP or the genes encoding the PSEN1 and PSEN2 proteins present in the γ-secretase complex; however, those inheriting a known AD-associated APP or PSEN1 variant will develop the disease, whereas a slightly lower risk (95%) is associated with inheriting a known AD variant in PSEN2 [54]. The gene discussed is PSEN1; the disease is Alzheimer disease.