C9orf72 and Alzheimer disease: In fewer than 5% of AD cases [3] and about 10% of FTD cases [4], these diseases are inherited as an autosomal dominant trait, by mutations in presenilin-1 (PSEN1), presenilin-2 (PSEN2) and the amyloid precursor protein (APP) genes, for AD [3], and microtubule-associated protein tau (MAPT), granulin (GRN) and chromosome 9 open reading frame 72 (C9orf72) genes, for FTD [5].