The literatures showed that individuals with TPMT deficiency who receive standard doses of thiopurines are at significant risk of toxicity, primarily as a result of unchecked production of 6-TGN.8–11 However, not all AEs or metabolite patterns can be explained by TPMT deficiency. The gene discussed is TPMT; the disease is hyperinsulinemic hypoglycemia, familial, 4.