FUS and amyotrophic lateral sclerosis: Notably, in a subsequent expansion of their study, the same investigators observed elevated CSF and serum levels of NFL in converters as far back as 6–12 months prior to phenoconversion in SOD1 mutation carriers, as far back as 2 years in the single converter with a FUS mutation, and as far back as 3.5 years in the single motor converter (i.e., developing ALS) with a C9orf72 HRE (Benatar et al., 2019).