C4A and amyotrophic lateral sclerosis: Recent studies have identified the involvement of the classical pathway of the complement system in the development of amyotrophic lateral sclerosis (ALS), with increased levels of C1q and C4 components observed in the cerebrospinal fluid, CNS, serum, and skeletal muscles of ALS patients (Apostolski et al., 1991; Tsuboi and Yamada, 1994; Yamada et al., 1994; Sta et al., 2011; Bahia El Idrissi et al., 2016).