HCAR2 and chronic obstructive pulmonary disease: After a long break, a part of the genetic component in the occurrence of COPD has been upgraded beyond 1-antitrypsin, with the genes for 1 nicotinic acid receptor, hedgehog interacting protein, Rho GTPase activating protein, etc. Nonetheless, so far identified genetic variants can explain only a small part of estimated COPD heritability [5].