Although children with de novo RET mutations are usually recognized because of symptomatic MTC or pheochromocytoma, our patient was discovered as a de novo M918T mutation carrier due to nonendocrine disease manifestations (intestinal neuronal dysplasia, tetralogy of Fallot, hypothyroidism, bilateral pyelectasis, short stature, and hypermobility syndrome) (5). The gene discussed is RET; the disease is medullary thyroid gland carcinoma.