Nonetheless, these species have been successfully developed into experimental animal models for AD by expressing pathogenic mutations that are found in the genes encoding APP, presenilin-1, and presenilin-2 in familial early-onset AD as well as by expressing pathogenic mutations in the tau-encoding MAPT (microtubule-associated protein tau) gene found in familial cases of FTLD (FTDP-17t) [15]. This evidence concerns the gene PSEN2 and Alzheimer disease.