NPPB and chronic obstructive pulmonary disease: The percentage of the rs6668352 site homozygous mutation of the BNP gene in the COPD group was significantly higher than that in the control group (adjusted OR = 1.327, 95% CI = 1.158–1.463, P<0.001), and the risk of COPD in the A allele carriers increased significantly (adjusted OR = 1.199, 95% CI = 1.108–1.288, P<0.001).