Pathogenetic mutations in three genes, namely beta-amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2), which induce an overproduction of the Aβ peptide, cause an early-onset (before age 65) autosomal dominant familial inherited form of the disease, representing a small percentage (<1%) of AD cases [11]. The gene discussed is PSEN2; the disease is Alzheimer disease.