APP and Alzheimer disease: Regarding age of onset of FTD, FUS gene mutations have been associated with age of onset ≤40 years of age [21]; on the other hand, early onset cases of alzheimer disease (AD) have been reported to be associated with mutations in the genes encoding for presenilin 1 (PS1) on chromosome 14, presenilin 2 (PS2) on chromosome 1, and the amyloid β-protein precursor (APP) on chromosome 21 [13].