C9orf72 and frontotemporal dementia: It is known that dormant inherited mutations relating to amyloid β (Aβ) synthesis in familial AD include APP, PSEN1, and PSEN2, and variants relating to the deposition of multiple abnormal proteins in FTD include MAPT, GRN, SQSTM1, TARDBP, C9orf72, and ERBB4, etc (Sun et al., 2020).