The subgroup analysis stratified by control type (healthy control group [HC] and disease control group [DC]) suggested that CSF MCP-1 levels were increased in ALS patients as compared to HC subjects (4 studies, Hedges' g = 0.520, 95% CI = 0.297 to 0.743, P < 0.001), or DC subjects(15 studies, Hedges' g = 0.607, 95% CI = 0.254 to 0.960, P = 0.001), and no heterogeneity was found for the HC group (Q = 1.724, d.f. = 3, I2 = 0.000, P = 0.632), whereas the impact of heterogeneity was slightly increased for the DC group (Q = 48.772, d.f. = 14, I2 = 71.295, P < 0.001). Here, CCL2 is linked to amyotrophic lateral sclerosis.