Early-onset AD is a rare hereditary form of the disease that accounts for ~5-10% of all cases and a minority of early-onset cases has been linked to specific mutations in the genes encoding amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) (1, 2). The gene discussed is PSEN2; the disease is Alzheimer disease.