TREM2 and frontotemporal dementia: Markers of phagocytic microglia, TREM2 and CD68, were increased in FTD-C9orf72 and FTD-GRN, indicating that both gene defects promote a phagocytic microglial phenotype, however our evidence indicates that hyperactive myelin lipid catabolism differentiates FTD-GRN from FTD-C9orf72 cases.