TREM2 and frontotemporal dementia: Levels of lysosomal markers and the microglial lipid receptor TREM2 were increased in both FTD-C9orf72 and FTD-GRN cases, whereas galactocerebrosidase activity, required for catabolism of the myelin lipids galactosylceramide and ST, was only significantly increased in FTD-GRN cases.