MAD1L1 and gastroesophageal reflux disease: These intracellular signaling pathways include the MAD1L1 gene, as well as genes that encode numerous class A GPCRs including proteinase-activated receptors, as well as opioid, dopamine, acetylcholine muscarinic, and chemokine receptors, among others, implicated in both GERD and COPD pathogenesis [30–36].