There are two varieties of AD: “early onset forms” (ADAD, less than 5% of all cases) connected to mutations in the presenilin 1/2 (PS-1/2) and amyloid precursor protein (APP) genes and “late-onset AD” (LOAD), the most frequent sporadic form of the illness [18,19]. The gene discussed is PSEN1; the disease is Alzheimer disease.