Neurofilament light chain (NfL) has been found to be increased in serum and plasma of numerous neurologic conditions, including amyotrophic lateral sclerosis (ALS) and inherited peripheral neuropathies, and to be a promising tool to monitor disease progression.10,11 We here use the currently most sensitive methodology to measure NfL in patients with SBMA and in a rodent model of disease,12 and compare this marker of neuronal damage with measures of muscle damage and loss. The gene discussed is NEFL; the disease is amyotrophic lateral sclerosis.