C9 and amyotrophic lateral sclerosis: Blood Nf proteins (Nf‐L and Nf‐H) were also elevated in all ALS subgroups (ALS‐F, ALS‐S, and C9+ve ALS) compared to HC‐1 (Fig. 1F, p < 0.0001), with the highest level of expression in ALS‐F compared to HC (p < 0.0001), ALS‐S (p = 0.002), and C9+ve ALS (Fig. 1G, p = 0.0001).