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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=William J Gibson
|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
Line 8: Line 8:
|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
Line 20: Line 21:
|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.  Appropriate work-up is performed; and the patient is diagnosed with tetralogy of Fallot. In the patient's pre-operative chest x-ray report, the radiologist notes an absence of the thymic shadow. The patient then undergoes surgery that successfully corrects his cyanosis. Over the next few days, he suffers a seizure that is attributed to low calcium blood levels. Which of the following abnormalities 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]] is caused by a [[microdeletion]] within chromosome 22q11 that results in the abnormal embryological development of the third and the fourth [[branchial pouch]]es. These pouches normally give rise to the [[thymus]] and the [[parathyroid glands]].  
 
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.
Patients with DiGeorge syndrome suffer from congenital heart disease, especially conotruncal malformations (such as [[tetralogy of Fallot]], [[interrupted aortic arch]], [[ventricular septal defect]] ([[VSD]]), and [[truncus arteriosus]]), characteristic facial features, and [[thymic hypoplasia]] or aplasia, which is characterized by loss of thymic shadow on chest x-ray and results i. Loss of thymus function results in T-cell immune deficiency and susceptibility to overwhelming infections. Also patients with DiGeorge syndrome often have palatal abnormalities (such as [[velopharyngeal incompetence]], [[cleft palate]], or [[bifid uvula]]) and underactive parathyroid glands, which cause [[hypocalcemia]] and hypocalcemia-induced seizures among neonates. Notably thymic hypo/aplasia is not specific for DiGeorge syndrome; patients with Bruton's agammaglobulinemia and severe combined immunodeficiency disorder (SCID) may also have thymic hypo/aplasia with loss of thymic shadow on chest x-ray.


|AnswerA=Abnormal development of the 1st branchial pouch
Salient features can be summarized using the mnemonic CATCH-22 to describe DiGeorge syndrome:<br />
|AnswerAExp=[[DiGeorge syndrome]] is caused by abnormal development of the third and fourth [[branchial pouches]].
'''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<br />'''22''': Chromosome 22 microdeletion
|AnswerB=Abnormal development of the 2nd branchial pouch
|AnswerA=Abnormal development of the 1st and 2nd branchial pouches
|AnswerBExp=[[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]].
|AnswerC=Microdeletion on 7q
|AnswerB=Abnormal development of the 2nd and 3rd branchial pouches
|AnswerCExp=Microdeleion of a region on 7q causes [[William’s syndrome]]. The patient in this vignette has DiGeorge syndrome.
|AnswerBExp=[[DiGeorge syndrome]] is caused by abnormal development of the 3rd and 4th branchial pouches.
|AnswerD=Microdeletion on chromosome 15
|AnswerC=Presence of a Barr body
|AnswerDExp=Microdeletion of a region on chromosome 15 causes either [[Prader-Wili]] or [[Angelman]]’s syndromes.
|AnswerCExp=Presence of [[Barr body]], an inactive X chromosome in a female somatic cell, is a normal finding only in women. X chromosomes are inactivated by a process called [[lyonization]]. Presence of a Barr body in men is observed among patients with Klinefelter syndrome (karyotype 47, XXY). DiGeorge syndrome in a male patient is not associated with detection of a Barr body.
|AnswerE=Microdeletion on chromosome 22
|AnswerD=Abnormal development of the branchial pouch responsible for the development of the thymus only
|AnswerEExp=DiGeorge syndrome is caused by a microdeletion on chromosome 22.
|AnswerDExp=The 3rd branchial pouch is responsible for the development of the inferior parathyroid glands (dorsal wings) and the thymus (ventral wings). However, the 3rd branchial pouch is not the only involved branchial pouch in DiGeorge syndrome. The 4th branchial pouch, which is responsible for the development of the superior parathyroids (dorsal wings), is also involved.
|EducationalObjectives=DiGeorge syndrome is caused by a microdeletion on chromosome 22.
|AnswerE=A microdeletion
|References=First Aid 2014 page 91
|AnswerEExp=[[DiGeorge syndrome]] is caused by a microdeletion within chromosome 22.
|EducationalObjectives=[[DiGeorge syndrome]] is caused by a microdeletion on chromosome 22q11. It results in the abnormal development of the 3rd and 4th branchial pouches. Signs, symptoms, and features of DiGeorge syndrome are:<br>
'''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<br />'''22''': Chromosome 22 microdeletion
|References=Wilson DI, Burn J, Scambler P, et al. DiGeorge syndrome: part of CATCH 22. J Med Genet. 1993;30(10):852-6.
First Aid 2014 page 91
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=Immunodeficiency, Genetics, T cell, Thymus, Infection. Cardiology, Tetralogy of Fallot,
|WBRKeyword=Immunodeficiency, Genetics, T cell, Thymus, Infection. Cardiology, Tetralogy of Fallot,
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 23:22, 27 October 2020
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. Appropriate work-up is performed; and the patient is diagnosed with tetralogy of Fallot. In the patient's pre-operative chest x-ray report, the radiologist notes an absence of the thymic shadow. The patient then undergoes surgery that successfully corrects his cyanosis. Over the next few days, he suffers a seizure that is attributed to low calcium blood levels. Which of the following abnormalities 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::Presence of a Barr body
Answer C Explanation [[AnswerCExp::Presence of Barr body, an inactive X chromosome in a female somatic cell, is a normal finding only in women. X chromosomes are inactivated by a process called lyonization. Presence of a Barr body in men is observed among patients with Klinefelter syndrome (karyotype 47, XXY). DiGeorge syndrome in a male patient is not associated with detection of a Barr body.]]
Answer D AnswerD::Abnormal development of the branchial pouch responsible for the development of the thymus only
Answer D Explanation [[AnswerDExp::The 3rd branchial pouch is responsible for the development of the inferior parathyroid glands (dorsal wings) and the thymus (ventral wings). However, the 3rd branchial pouch is not the only involved branchial pouch in DiGeorge syndrome. The 4th branchial pouch, which is responsible for the development of the superior parathyroids (dorsal wings), is also involved.]]
Answer E AnswerE::A microdeletion
Answer E Explanation [[AnswerEExp::DiGeorge syndrome is caused by a microdeletion within chromosome 22.]]
Right Answer RightAnswer::E
Explanation [[Explanation::DiGeorge syndrome or 22q.11 syndrome is caused by a microdeletion within chromosome 22q11 that results in the abnormal embryological development of the third and the fourth branchial pouches. These pouches normally give rise to the thymus and the parathyroid glands.

Patients with DiGeorge syndrome suffer from congenital heart disease, especially conotruncal malformations (such as tetralogy of Fallot, interrupted aortic arch, ventricular septal defect (VSD), and truncus arteriosus), characteristic facial features, and thymic hypoplasia or aplasia, which is characterized by loss of thymic shadow on chest x-ray and results i. Loss of thymus function results in T-cell immune deficiency and susceptibility to overwhelming infections. Also patients with DiGeorge syndrome often have palatal abnormalities (such as velopharyngeal incompetence, cleft palate, or bifid uvula) and underactive parathyroid glands, which cause hypocalcemia and hypocalcemia-induced seizures among neonates. Notably thymic hypo/aplasia is not specific for DiGeorge syndrome; patients with Bruton's agammaglobulinemia and severe combined immunodeficiency disorder (SCID) may also have thymic hypo/aplasia with loss of thymic shadow on chest x-ray.

Salient features can be summarized using the mnemonic CATCH-22 to describe DiGeorge syndrome:
Cardiac Abnormality (especially tetralogy of Fallot)
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcemia/Hypoparathyroidism
22: Chromosome 22 microdeletion
Educational Objective: DiGeorge syndrome is caused by a microdeletion on chromosome 22q11. It results in the abnormal development of the 3rd and 4th branchial pouches. Signs, symptoms, and features of DiGeorge syndrome are:
Cardiac Abnormality (especially tetralogy of Fallot)
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcemia/Hypoparathyroidism
22: Chromosome 22 microdeletion
References: Wilson DI, Burn J, Scambler P, et al. DiGeorge syndrome: part of CATCH 22. J Med Genet. 1993;30(10):852-6. 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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