WBR0112

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology, MainCategory::Genetics, MainCategory::Immunology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A newborn boy is found to be cyanotic following a natural birth. He is found to have Tetralogy of fallot and undergoes surgery which successfully corrects his cyanosis. Over the next few years, the boy suffers an unusually large number of severe bacterial infections. His pediatrician requests a chest x-ray and the radiologist notes an absence of the thymic shadow. Which of the following is most likely to have caused this child’s condition?]]
Answer A	AnswerA::Abnormal development of the 1st branchial pouch
Answer A Explanation	AnswerAExp::Incorrect - DiGeorge syndrome is caused by abnormal development of the thrid and fourth branchial pouches.
Answer B	AnswerB::Abnormal development of the 2nd branchial pouch
Answer B Explanation	AnswerBExp::Incorrect - DiGeorge syndrome is caused by abnormal development of the third and fourth branchial pouches.
Answer C	AnswerC::Microdeletion on 7q
Answer C Explanation	AnswerCExp::Incorrect - Microdeleion of a region on 7q causes William’s Syndrome.
Answer D	AnswerD::Microdeletion on chromosome 15
Answer D Explanation	AnswerDExp::Incorrect - Microdeletion of a region on chromosome 15 causes either Prader-Wili or Angelman’s syndromes.
Answer E	AnswerE::Microdeletion on chromosome 22
Answer E Explanation	AnswerEExp::Correct - See explanation
Right Answer	RightAnswer::E
Explanation	[[Explanation::The patient in this vignette is suffering from DiGeorge Syndrome or 22q.11 syndrome. DiGeorge syndrome is caused by the deletion of a small piece of chromosome 22. Patients suffer from cardiac abnormalities (40%), and conditions resulting from abnormal development of the third and fourth branchial pouches. The third and fourth branchial pouches give rise to the thymus and the parathyroid glands. As a result, patients experience hypocalcemia due to deficiency of parathyroid hormone and immunodeficiency of T cells due to lack of a thymus. Educational Objective: References: ]]
Approved	Approved::Yes
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