<prompt> A 20 years old male presents with chronic constipation, headache and Marfanoid habitus, neuromas of tongue, medullated corneal nerve fibers and nodule of 2x2 cm size in the left lobe of thyroid. The most probable diagnosis is:Sporadic medullary carcinoma of thyroidFamilial medullary carcinoma of thyroidMEN 2AMEN 2B  <response>: - 2x2cm size of nodule most commonly medullary thyroid carcinoma - Headache because of pheochromocytoma - Therefore, diagnosis is MEN-2B MEN-2B Also known as MEN-3 Gene mutated is tyrosine kinase codon of RET oncogene. Pheochromocytoma M - MTC most aggressive M - marfanoid features M - mucosal neuromas. RET oncogene tyrosine kinase domain Autosomal dominant 