NEFL and early-onset autosomal dominant Alzheimer disease: Neurofilament light chain (NfL) is a sensitive marker of neurodegeneration.8 CSF NfL is elevated in patients with FTLD compared to patients with Alzheimer disease and healthy controls,9, -, 12 with concentrations that correlate with disease severity, cognitive function, and disease progression.13,14 CSF NfL concentrations normalize on effective treatment in multiple sclerosis15 and spinal muscle atrophy,16 suggesting that NfL is sensitive to treatment effects.