The rate of disability progression for an individual with ALS is largely stable throughout the disease course and longitudinal analysis of CSF NFL was consistent with the stability of levels seen in a previous study.9,26 Plasma NFL showed a previously observed slow rise in level,27 which may be driven by patients with a shorter latency from the first symptom to the first assessment. The gene discussed is NEFL; the disease is amyotrophic lateral sclerosis.