Although Meeter et al. (2016, 2018b) reported a weak association of CSF NFL with disease duration at sampling in their large FTD cohort, the finding has not been replicated in studies investigating serum NFL in bvFTD and PPAs and CSF or serum NFL in genetic forms of FTD (Meeter et al., 2016, 2018b; Steinacker et al., 2017b, 2018; van der Ende et al., 2019). The gene discussed is NEFL; the disease is behavioral variant of frontotemporal dementia.