ADORA2B and chronic obstructive pulmonary disease: CYSLTR1 (+ 348, Fig. 2G), CCDC88C (+ 125,722, Fig. 2H), and ADORA2B (+ 1339, Fig. 2I) genes were all hypomethylated in COPD patients with severe to very severe airflow limitation (GOLD III-IV) versus those with mild to moderate airflow limitation (GOLD I-II), while TIGIT gene (− 173, Fig. 2J) was hypermethylated.