CHRNA3 and chronic obstructive pulmonary disease: 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].