HHIP and chronic obstructive pulmonary disease: Other studies on genetic polymorphisms have identified several genes associated with the pathogenesis of different characteristics of COPD: cholinergic nicotine receptor alpha 3/5 (CHRNA3/5), iron regulatory binding protein 2 (IREB2), hedgehog-interacting protein (HHIP), family with sequence similarity 13, member A (FAM13A), and advanced glycosylation end product-specific receptor (AGER) [70,71,72,73,74,75].