PSEN2 and familial Alzheimer disease: While sporadic AD is due to a complex combination of genes, environmental factors, or lifestyle [7], familial AD (FAD) is caused by a mutation in one of three genes known as the amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) genes, which account for at least 103, 350, and 80 mutations, respectively (https://www.alzforum.org/mutations; accessed January 2025).