MUC6 and chronic obstructive pulmonary disease: Among COPD subjects with ≥10% emphysema, chromosome 11p15.5, which includes genes AP2A2, MUC6 and CHID1, was the most significant region (rs7483870, β = 0.16L, P = 3.93 × 10−7; rs4076950, β = 0.13L, P = 2.88 × 10−6; rs4963123, β = 0.13L, P =3.40 × 10−6).