AD is a non-curable neurodegenerative disease with the majority of cases (85–90%) being sporadic and just 10–15% familial and caused by mutations in key genes such as Amyloid Precursor Protein (APP), Presenilin 1 (PSEN1), and Presenilin 2 (PSEN2), involved in the metabolic pathway of APP. The gene discussed is PSEN1; the disease is Alzheimer disease.