C9 and amyotrophic lateral sclerosis: Plasma Nf‐L ICs were significantly elevated in both ABC and PGB compared to HC‐1 and HC‐2, respectively (p < 0.0001; Fig. 2C and D), while among ALS variants, the highest levels of Nf‐L ICs blood concentration were found in ALS‐F and in C9+ve ALS patients compared to HC, in both ABC (p < 0.0001 and p = 0.0003) and PGB (p < 0.0001 and p = 0.0025), and in ALS‐S compared to HC (PGB cohort, p = 0.015; Fig. 2C and D).