NFL has been investigated in patients with genetic FTD, i.e., those carrying mutations in the three main genes MAPT, GRN, and C9orf72. Most studies on CSF NFL report higher levels in patients with GRN mutations compared with patients without known gene mutations, patients with MAPT mutations or the C9orf72 HRE, or patients with FTLD-tau as neuropathologically or genetically defined (Meeter et al., 2016, 2018b; Goossens et al., 2018). This evidence concerns the gene C9orf72 and frontotemporal dementia.