PPP3R1 and Alzheimer disease: The most prominent AD-associated susceptible genes and their altered expression/splicing/translation/PTM (posttranslational modifications), such as APP and PSEN1 [23, 45], APOE and APOER2 [46], PTK2B [47], PPP3CA and PPP3R1 [48, 49], and PIN1 [50], are involved in synaptic homeostasis.