WBR0112
| Author | [[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D. and Rim Halaby, M.D. [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Embryology, MainCategory::Genetics, MainCategory::Immunology |
| Sub Category | SubCategory::Cardiology, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A newborn boy is found to be cyanotic following birth by normal vaginal delivery. Following appropriate work-up, the patient is diagnosed with tetralogy of Fallot. The radiologist notes an absence of the thymic shadow in the patient's pre-operative chest x-ray. The patient then undergoes surgery that successfully corrects his cyanosis. Over the next few days, he suffers a seizure and is found to have low calcium blood levels. Which of the following most likely caused this child’s condition?]] |
| Answer A | AnswerA::Abnormal development of the 1st and 2nd branchial pouches |
| Answer A Explanation | [[AnswerAExp::DiGeorge syndrome is caused by abnormal development of the 3rd and 4th branchial pouches.]] |
| Answer B | AnswerB::Abnormal development of the 2nd and 3rd branchial pouches |
| Answer B Explanation | [[AnswerBExp::DiGeorge syndrome is caused by abnormal development of the 3rd and 4th branchial pouches.]] |
| Answer C | AnswerC::Microdeletion on 7q |
| Answer C Explanation | [[AnswerCExp::Microdeleion of a region on 7q causes William’s syndrome. The patient in this vignette has signs and symptoms of DiGeorge syndrome.]] |
| Answer D | AnswerD::Microdeletion on chromosome 15 |
| Answer D Explanation | [[AnswerDExp::Microdeletion of a region on chromosome 15 causes either Prader-Willi or Angelman’s syndromes.]] |
| Answer E | AnswerE::Microdeletion on chromosome 22 |
| Answer E Explanation | AnswerEExp::DiGeorge syndrome is caused by a microdeletion on chromosome 22. |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::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. The unusually large number of infections in this patient is due to said T cell deficiency.
Salient features can be summarized using the mnemonic CATCH-22 to describe DiGeorge syndrome, with the 22 to remind one the chromosomal abnormality is found on the 22 chromosome, as below: Cardiac Abnormality (especially tetralogy of Fallot) |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Immunodeficiency, WBRKeyword::Genetics, WBRKeyword::T cell, WBRKeyword::Thymus, WBRKeyword::Infection. Cardiology, WBRKeyword::Tetralogy of Fallot |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |