An independently accurate diagnostic biomarker for ALS seems most likely to be related to the TDP-43 proteinopathy that characterizes nearly all cases of ALS.23 Meanwhile, the most consistent role of blood NfL currently is in the context of an established diagnosis of ALS, with many studies showing a robust correlation of NfL level with rate of disability progression rate. The gene discussed is NEFL; the disease is amyotrophic lateral sclerosis.