Several studies have demonstrated that the activity of protein phosphatase 2A (PP2A) and serine/threonine-protein phosphatase (PP2B) is decreased in AD mouse models and patients (58, 142) [reviewed in (59)], as well as in both Tg and knock-in HD mouse models (56, 64, 143) (Table 1). This evidence concerns the gene PTPA and Alzheimer disease.