APP and Alzheimer disease: Till now, at least 3 causal genes and 22 risk genes have been identified to be involved in the pathogenesis of AD, including amyloid precursor protein (APP), presenilin-1/2 (PSEN1/2) [5, 13], apolipoprotein E (APOE) [14], ABCA7, BIN1, CASS4, CD33, CD2AP, CELF1, CLU, CR1, DSG2, EPHA1, FERMT2, HLA-DRB5-DBR1, INPP5D, MS4A, MEF2C, NME8, PICALM, PTK2B, SORL1, SLC24H4-RIN3, and ZCWPW1 [15].