In other neurological disorders, including Multiple Sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD), neurofilament light chain levels (NfL) in body fluids such as serum, plasma or CSF may provide a biomarker for tracking disease activity including progression (Bridel et al., 2019; Forgrave et al., 2019; Aktas et al., 2020; Del Prete et al., 2020; Milo et al., 2020; Thebault et al., 2020; Wang et al., 2020). The gene discussed is NEFL; the disease is early-onset autosomal dominant Alzheimer disease.