Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) syndrome is a rare but potentially life-threatening hypersensitivity reaction to certain medications, including allopurinol (a xanthine oxidase inhibitor), antiepileptics (e.g., phenytoin, carbamazepine), and antibiotics (e.g., vancomycin). The gene discussed is XDH; the disease is drug hypersensitivity syndrome.