Previous studies have demonstrated that the prevalence of early-onset AD is rather low (< 5%), and commonly associated with autosomal-dominant genetic mutations, which include mutations in the genes encoding for the amyloid-beta precursor protein (APP) (20, 21) as well as in the presenilin 1 (PSEN1) and 2 (PSEN2) genes (22). The gene discussed is PSEN1; the disease is Alzheimer disease.