Thirdly, the association of Skeletal Muscle Atrophy with COPD could be explained not by IREB2 but by linkage disequilibrium with SNPs near CHRNA3 and CHRNA5 [42], encoding nicotinic acetylcholine receptors that respond to the acetylcholine neurotransmitter as well as nicotine [47]. Here, CHRNA5 is linked to chronic obstructive pulmonary disease.