NEFL and amyotrophic lateral sclerosis: Natural history studies have demonstrated elevated NfL levels in comparison to age-matched healthy controls in Huntington’s disease (HD) [7, 8], multiple sclerosis (MS) [9], amyotrophic lateral sclerosis (ALS) [10], frontotemporal dementia [11], and Alzheimer’s disease [12], including those in the very early stages of disease [13, 14].