Such pseudo-allergic reactions manifest as clinical pictures mimicking allergy, depending on the cells/mediators involved: e.g., the mast cells with urticarial/anaphylaxis are involved in off-target pharmacological activities of certain drugs on mast cells receptors (MRGPRX2); the blocking of enzymes like cyclooxygenase in nonsteroidal anti-inflammatory drugs (NSAID) can lead to exacerbated asthma or urticaria; and blocking the degradation of bradykinin by angiotensin converting enzyme (ACE) inhibitors may lead to angioedema. This evidence concerns the gene ACE and allergic disease.