Several studies have suggested that the concentrations of Ng are increased in cerebrospinal fluid (CSF) (De Vos et al., 2015; Hellwig et al., 2015; Kvartsberg et al., 2015b; Portelius et al., 2015; Janelidze et al., 2016) and decreased in the brain of patients with AD (Davidsson and Blennow, 1998; Reddy et al., 2005; Kvartsberg et al., 2019). Here, NRGN is linked to Alzheimer disease.