C3 and amyotrophic lateral sclerosis: Additionally, genes linked to the alternative complement pathway were increased in ALS motor neurons, including complement C3 (C3) (SMD = 1.15, p = 0.00113, FDR = 0.036) and complement C3a receptor 1 (C3AR1) (SMD = 1.66, p = 5.9e-07, FDR = 0.00114).