C9orf72 and frontotemporal dementia: It is estimated that 60% of patients with FTD have autosomal dominant mutations in C9orf72, GRN, or MAPT genes.316 Additionally, mutations in TBK1 are associated with developing FTD,317,318 and variants in TREM2 increase an individual’s risk of developing FTD.319 In vivo PET studies320,321 and immunohistochemistry studies322–324 have found increased microglial activation in the frontal and temporal cortices of patients with FTD.