CHRNA5 and chronic obstructive pulmonary disease: Previous GWAS have identified three susceptibility loci for COPD, including HHIP (hedgehog interacting protein [MIM 606178]), FAM13A (family with sequence similarity 13, member A [MIM 613299]), and a multi-gene locus on chromosome 15q25 containing candidate genes CHRNA5 (cholinergic receptor, nicotinic, alpha 5 [MIM 118505]), CHRNA3 (MIM 118503), and IREB2 (iron-responsive element binding protein 2 [MIM 147582]) [11]–[13].