Using plasma obtained at baseline and follow-up visits, we measured GFAP and NfL in plasma from clinically normal, mutation-negative individuals from kindreds with an FTD-causing mutation (controls, N = 161), presymptomatic individuals with a C9orf72 repeat expansion or a GRN or MAPT mutation (N = 127), and participants with sporadic or genetic bvFTD (N = 308), nfvPPA (N = 76), svPPA (N = 83), CBS (N = 92) or PSP-RS (N = 143). The gene discussed is CBS; the disease is frontotemporal dementia.