CHRNA1 and chronic obstructive pulmonary disease: Additionally, 5 variants (TGF-β1 rs1800469, MMP-1 rs1799750, SERPINE2 rs3795879, and CHRNA rs578776 and rs588765) in 4 genes showed convincing evidence of no association with COPD risk in meta-analyses that included a minimum of 2400 cases and 3000 controls [34, 62, 67, 68].