NEFL and amyotrophic lateral sclerosis: The finding of elevated CSF and serum NfL levels in patients, with a good diagnostic performance to separate them from presymptomatic carriers, confirms the earlier findings in small series of presymptomatic carriers.10, 15 The strong correlation between CSF and serum NfL levels, alike in ALS,15, 18 suggests a promising role for serum NfL as a biomarker, as blood collections are more patient friendly than lumbar punctures.