C9orf72 and frontotemporal dementia: However, microglial function is complex and is likely influenced not only by mutations in FTD-associated genes known to affect microglial or lysosomal function (such as GRN, C9orf72, MAPT, TBK1, SQSTM1, VCP or CHMP2B), but also by polygenic variants in immune system genes linked to FTD, such as HLA loci [81, 82] or TREM2 [83, 84] and in lysosomal genes linked to variability in FTLD-GRN and FTLD-C9orf72 such as TMEM106B, SORT1 and PSAP [79, 85–88].