NEFL and amyotrophic lateral sclerosis: The same study showed a gradient of CSF NFL concentrations with the highest levels in ALS, intermediate levels in ALS-FTD, and lowest levels in FTD; however, the only statistically significant differences were those between ALS and FTD and between ALS and ALS-FTD, whereas ALS-FTD did not significantly differ from FTD alone (Delaby et al., 2020).