Contrary to the well-validated cerebrospinal fluid (CSF) biomarkers in Alzheimer’s disease, an early specific fluid biomarker for FTD is lacking.2 Emerging studies report elevated levels of neurofilament light chain (NfL) in FTD than in various other neurodegenerative disorders, indicating a role as a diagnostic biomarker. This evidence concerns the gene NEFL and early-onset autosomal dominant Alzheimer disease.