Blood NfL is robustly increased in AD (Mattsson et al., 2017; Lin et al., 2018; Ashton et al., 2019b; Preische et al., 2019) but is also increased in many other neurodegenerative disorders and acute neurological disorders (Hansson et al., 2017; Ehler et al., 2019; Hendricks et al., 2019; Mattsson et al., 2019; Ashton et al., 2020; Kapoor et al., 2020; Wihersaari et al., 2021). The gene discussed is NEFL; the disease is Alzheimer disease.