Increased NfL levels in cases compared to age‐matched controls are present in the cerebrospinal fluid (CSF) across a range of conditions characterized by neuronal and axonal degeneration including multiple sclerosis, Alzheimer’s disease, amyotrophic lateral sclerosis, frontotemporal dementia, HIV‐associated dementia, etc.1, 2 The recently developed single molecule array can detect very low concentrations of leaked NfL (pg/mL) from CSF in blood. This evidence concerns the gene NEFL and multiple sclerosis.