MAPT and Alzheimer disease: PPP1CA is one of three catalytic subunits of the serine/threonine specific protein phosphatase 1 (PP1), which is known to be involved in the regulation of glycogen metabolism, cell division, muscle contractility and protein synthesis (44). PPP1CA itself is linked to diverse tumor entities and is involved in ERK/MAPK signaling (45, 46), TGFβ signaling (47), Ras signaling and Ras-induced senescence (48), spermatogenesis (49) as well as in tau hyperphosphorylation leading to Alzheimer's disease (50).