NEFL and Alzheimer disease: This seems to be in contrast with the evidence of an association between high NfL levels and shorter survival in FTD, progressive supranuclear palsy, Alzheimer’s disease (AD) and amyotrophic lateral sclerosis.5 6 10 11 However, the median follow-up time of the entire cohort in our study was 4.3 years (IQR: 2.6–6.0), which is relatively short considering average survival which ranges from 9 to 12 years in SD.16 17 Since the follow-up time may have been too short to capture the differences in survival, we propose to reinvestigate the survival of the current cohort in approximately 3–5 years.