CCL2 and amyotrophic lateral sclerosis: For the non-ELISA method, there was no significant heterogeneity among studies (Q = 2.393, d.f. = 3, I2 = 0, P = 0.495), and the significant association between CSF MCP-1 and ALS was retained (4 studies, Hedges' g = 0.696, 95% CI = 0.40 to 0.962, P < 0.001).