WBR248

Author	PageAuthor::Gerald Chi
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics, MainCategory::Pathology
Sub Category	SubCategory::Dermatology, SubCategory::Endocrine, SubCategory::Oncology
Prompt	[[Prompt::A male newborn is evaluated for vomiting due to failure to pass his first stool within 48 hours of birth. The vomit is approximately two teaspoons in volume, green-brownish in color, without bloody contents. His abdomen is distended and digital rectal examination elicits massive passage of gas and stools. Diagnosis is made by a rectal biopsy showing the lack of migration of ganglions due to mutation of a proto-oncogene. Which of the following conditions is associated with mutation of this gene?]]
Answer A	AnswerA::Café au lait macules
Answer A Explanation	[[AnswerAExp::Incorrect Café au lait macules may be associated with a wide variety of diseases including neurofibromatosis type I, McCune–Albright syndrome, tuberous sclerosis, Fanconi anemia, ataxia telangiectasia, Bloom syndrome, Chediak-Higashi syndrome, Gaucher disease, Hunter syndrome, and Wiskott–Aldrich syndrome.]]
Answer B	AnswerB::Cutaneous angiofibroma
Answer B Explanation	[[AnswerBExp::Incorrect Angiofibromas are reddish brown papules of 0.1 to 0.3 cm diameter that present over the sides of the nose and the medial portions of the cheeks. It may be assoicated with type 1 multiple endocrine neoplasia.]]
Answer C	AnswerC::Medullary thyroid carcinoma
Answer C Explanation	[[AnswerCExp::Correct Medullary thyroid cancer is a form of thyroid carcinoma which originates from the parafollicular cells that produce calcitonin. Approximately 25% of medullary thyroid cancer is genetic in nature, caused by a mutation in the RET proto-oncogene. Medullary thyroid carcinoma may be associated with multiple endocrine neoplasias type 2A and 2B.]]
Answer D	AnswerD::Pituitary prolactinoma
Answer D Explanation	[[AnswerDExp::Incorrect Pituitary prolactinoma is a benign tumor of the pituitary gland. It is the most common type of pituitary tumor. Symptoms of prolactinoma are caused by hyperprolactinemia or by pressure of the tumor on surrounding tissues. It may be associated with type 1 multiple endocrine neoplasia.]]
Answer E	AnswerE::Vasoactive intestinal peptide tumor
Answer E Explanation	[[AnswerEExp::Incorrect A VIPoma is an endocrine tumor usually originating from non-beta islet cesll of the pancreas that produce vasoactive intestinal peptide (VIP).The massive amounts of VIP cause profound, chronic watery diarrhea and dehydration, hypokalemia, achlorhydria, vasodilation, hypercalcemia and hyperglycemia. It may be associated with type 1 multiple endocrine neoplasia.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::When meconium becomes thickened and congested in the ileum, a condition known as meconium ileus, abdominal distension and vomiting occur soon after birth. Failure of passage of meconium may be associated with Hirschsprung's disease or cystic fibrosis. During normal fetal development, cells from the neural crest migrate into the colon to form Auerbach's plexus and Meissner's plexus. Hirschsprung's disease (HD) occurs when the migration is not complete and part of the colon lacks these nerve bodies that regulate the activity of the colon. The affected segment of the colon cannot relax and pass stool through the colon, creating an obstruction. In most affected people, the disorder affects the part of the colon that is nearest the anus. RET is a proto-oncogene that codes for proteins that assist cells of the neural crest in their movement through the digestive tract during the development of the embryo. It encodes a receptor tyrosine kinase for members of the glial cell line-derived neurotrophic factor family of extracellular signalling molecules. Loss-of-function mutations are associated with Hirschsprung's disease, while gain-of-function mutations are associated with medullary thyroid carcinoma, pheochromocytoma, and multiple endocrine neoplasias type 2A and 2B. Educational Objective: References: ]]
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