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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=William J Gibson (reviewed by {{Rim}})
|QuestionAuthor=William J Gibson (Reviewed by {{YD}} and {{Rim}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
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|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
|SubCategory=Cardiology, Infectious Disease
|SubCategory=Cardiology, Infectious Disease
|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
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|MainCategory=Embryology, Genetics, Immunology
|MainCategory=Embryology, Genetics, Immunology
|SubCategory=Cardiology, Infectious Disease
|SubCategory=Cardiology, Infectious Disease
|Prompt=A newborn boy is found to be cyanotic following a natural birth. He is diagnosed with tetralogy of Fallot and undergoes surgery that 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?
|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?
|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.  The unusually large number of infections in this patient is due to said T cell deficiency.
|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:
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:


'''C'''ardiac Abnormality (especially [[tetralogy of Fallot]])<br />'''A'''bnormal [[Facies (medical)|facies]] <br />'''T'''hymic aplasia <br />'''C'''left palate <br />'''H'''ypocalcemia/'''H'''ypoparathyroidism.
'''C'''ardiac Abnormality (especially [[tetralogy of Fallot]])<br />'''A'''bnormal [[Facies (medical)|facies]] <br />'''T'''hymic aplasia <br />'''C'''left palate <br />'''H'''ypocalcemia/'''H'''ypoparathyroidism.
|AnswerA=Abnormal development of the 1st branchial pouch
|AnswerA=Abnormal development of the 1st and 2nd branchial pouches
|AnswerAExp=[[DiGeorge syndrome]] is caused by abnormal development of the third and fourth [[branchial pouches]].
|AnswerAExp=[[DiGeorge syndrome]] is caused by abnormal development of the 3rd and 4th [[branchial pouches]].
|AnswerB=Abnormal development of the 2nd branchial pouch
|AnswerB=Abnormal development of the 2nd and 3rd branchial pouches
|AnswerBExp=[[DiGeorge syndrome]] is caused by abnormal development of the third and fourth branchial pouches.
|AnswerBExp=[[DiGeorge syndrome]] is caused by abnormal development of the 3rd and 4th branchial pouches.
|AnswerC=Microdeletion on 7q
|AnswerC=Microdeletion on 7q
|AnswerCExp=Microdeleion of a region on 7q causes [[William’s syndrome]]. The patient in this vignette has DiGeorge syndrome.
|AnswerCExp=Microdeleion of a region on 7q causes [[William’s syndrome]]. The patient in this vignette has signs and symptoms of DiGeorge syndrome.
|AnswerD=Microdeletion on chromosome 15
|AnswerD=Microdeletion on chromosome 15
|AnswerDExp=Microdeletion of a region on chromosome 15 causes either [[Prader-Willi]] or [[Angelman's syndrome|Angelman]]’s syndromes.
|AnswerDExp=Microdeletion of a region on chromosome 15 causes either [[Prader-Willi]] or [[Angelman's syndrome|Angelman]]’s syndromes.

Revision as of 20:26, 9 September 2014
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)
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcemia/Hypoparathyroidism.
Educational Objective: DiGeorge syndrome is caused by a microdeletion on chromosome 22.
References: First Aid 2014 page 91]]

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::
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