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). This evidence concerns the gene RET and hypothyroidism.