Strengths of our study include measuring, in a blinded manner and at one site, both plasma GFAP and NfL in a large series of well-characterized individuals diagnosed with bvFTD, nfvPPA, svPPA, PSP and CBS along with presymptomatic mutation carriers and controls; performing head-to-head comparisons of GFAP and NfL; including cross-sectional and longitudinal assessments of both biomarkers; examining the prognostic potential of each biomarker in each syndrome separately; and evaluating the combined use of GFAP and NfL to inform pathology in participants with FTD. The gene discussed is CBS; the disease is frontotemporal dementia.