As a result, MRGPRX2 is responsible for mediating mast cell anaphylactic and pseudo-allergic reactions to several US Food and Drug Administration (FDA)-approved drugs (3, 9–14) and has been implicated in the pathology of chronic inflammatory diseases such as asthma (6), rosacea (15), and urticaria (5). The gene discussed is MRGPRX2; the disease is rosacea.