C9 and amyotrophic lateral sclerosis: In the CNS, the dysregulation in complement proteins (C1‐C9), mainly synthesized by the neurons and the glial cells, are found in pathological conditions, including Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), and Huntington's disease.[18, 19, 20, 21, 22] In normal conditions, selective elimination of unsuitable synapses takes place by the expression of C1q protein in a classical cascade,[23] initiated by the blockage of Ach release.