This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'Pheochromocytoma is a feature of all of the following except: September 2007 \nSelect and explain. \nA. MEN I syndrome, B. MEN II syndrome, C. Neurofibromatosis type I, D. Von Hippel-Lindau syndrome', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A: MEN I syndrome Pheochromocytoma are known to occur in ceain familial syndromes. These include MEN 2A and 2B, neurofibromatosis (von Recklinghausen disease), and Von Hippel-Lindau syndrome. The MEN 2A and 2B syndromes, which are autosomal dominantly inherited, have been traced to germline mutations in the ret (rearranged in transfection) proto-oncogene. The ret proto-oncogene, located on chromosome 10, encodes a tyrosine kinase receptor involved in the regulation of cell growth and differentiation. Pheochromocytomas occur bilaterally in the MEN syndromes in as many as 70% of cases. MEN 2A (Sipple syndrome) is characterized by medullary thyroid carcinoma, hyperparathyroidism, pheochromocytomas, and Hirschsprung disease. Over 95% of cases of MEN 2A are associated with mutations in the ret proto-oncogene affecting 1 of 5 codons in exon 10. MEN 2B is characterized by medullary thyroid carcinoma, pheochromocytoma, mucosal neurofibromatosis, intestinal ganglioneuromatosis, Hirschsprung disease, and a marfanoid body habitus. A germline missense mutation in the tyrosine kinase domain of the ret proto-oncogene (exon 16, codon 918) has been repoed to be present in 95% of patients with MEN 2B.', 'role': 'assistant'}]