APLNR and obesity due to melanocortin 4 receptor deficiency: As for patients with COPD, the Activin A Receptor Type 2B (ACVR2B) and Transforming Growth Factor Beta 1 (TGFβ1), which were the key modulators of BMPR2 pathway, were significantly downregulated, as well as the obesity-related gene Apelin Receptor Early Endogenous Ligand (APELA).