CCL2 and amyotrophic lateral sclerosis: Furthermore, the impact of heterogeneity was slightly increased (Q = 49.25, d.f. = 13, I2 = 73.605, P < 0.001), and the significant association between CSF MCP-1 and ALS was retained for the ELISA method (14 studies, Hedges' g = 0.528, 95% CI = 0.161 to 0.895, P = 0.005).