MERTK and frontotemporal dementia: At the protein level, MERTK but not AXL is decreased in CSF from symptomatic GRN-FTD patients (Fig. 6C) and is also decreased in human induced microglia (Supplementary Fig 4A, B) but is not different between post-mortem brain tissue from GRN+/− and GRN+/+ individuals (Supplementary Fig 4D, E).