This familial form of AD is due to alterations in three specific genes: presenilin-1 (PS1, on chromosome 14), presenilin-2 (PS2, on chromosome 1) and amyloid precursor protein (APP) that can be inherited as an autosomal dominant disorder and accounts for less than 1 % of the total number of AD cases [79, 82, 92]. The gene discussed is PSEN2; the disease is Alzheimer disease.