GRK4 and chronic obstructive pulmonary disease: In the COPD discovery set, seven candidate genes primarily located on chromosomes 4 and 22 (MFSD10, GRK4, PPA2, TET2, XPNPEP3, HTT, and NOP14-AS1) were further analyzed using COJO analysis within each tissue to validate their associations with COPD and eliminate potential false positives due to LD.