MRGPRX2 is a promiscuous receptor on mast cells that responds to a variety of exogenous and endogenous ligands, including Cortistatin 14 (CST-14), Compound 48/80 (Cpd 48/80) and a variety of pharmacological agents. It mediates IgE-independent degranulation and has been implicated in multiple mast cell-mediated disorders, such as chronic urticaria, atopic dermatitis, and pain disorders. Atheron discovered a novel, potent, and selective orally active small molecule MRGPRX2 antagonist, ATH-004 for potential treatment of mast cell-mediated disease.