SOD1 and amyotrophic lateral sclerosis: When stratifying ALS patients into spinal and bulbar onset groups, statistically significant differences in plasma NFL concentrations in spinal onset ALS patients were observed when comparing patients with C9orf72HRE mutations to both patients who were SOD1 mutation carriers (p < 0.01) and ALS patients with no known mutations (p < 0.05); however, there was no statistically significant difference among different genotype groups in bulbar onset ALS patients (p > 0.05 for overall ANOVA).