<prompt> Pheochromocytoma is a feature of all of the following except: September 2007MEN I syndromeMEN II syndromeNeurofibromatosis type IVon Hippel-Lindau syndrome  <response>: 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. 