AD's less frequent (1–5% of all cases) early onset (around 60 years) familial (autosomal dominant) form (EOFAD) is caused by mutations in genes encoding the amyloid precursor protein (APP) or presenilin 1 (PSEN1) or presenilin 2 (PSEN2). The gene discussed is PSEN1; the disease is early-onset autosomal dominant Alzheimer disease.