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Review Question - QID 106536

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QID 106536 (Type "106536" in App Search)
You are called to examine a one-hour-old baby who was born with a facial defect illustrated in Figure A. The patient's ears appear to be low-set. On auscultation, there is a holosystolic murmur along the lower left sternal border. Basic labs return notable for hypocalcemia. What is the most likely underlying mechanism responsible for the abnormalities seen in this newborn?
  • A

Trisomy 21



Trisomy 18



Trinucleotide repeat expansion



Partial deletion on chromosome 22



Uniparental disomy



  • A

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The clinical presentation is most consistent with microdeletion at chromosome 22q11.

Microdeletion at chromosome 22q11 results in abnormal development of the 3rd and 4th branchial pouches. This can cause a variable clinical presentation. Classically, 22q11 deletion can result in "CATCH-22" disease, which includes Cleft palate, Abnormal facies, Thymic aplasia, Cardiac abnormalities, and Hypocalcemia. DiGeorge syndrome and velocardiofacial syndrome represent two specific presentations of 22q11 microdeletions.

Solomon and Maximilian discuss when to suspect a genetic syndrome. While a cleft palate in a newborn has a broad differential diagnosis, the additional findings of hypocalcemia and ventricular septal defect (causing holosystolic murmur at the lower left sternal border) are highly suggestive of 22q11 microdeletion. Additional subtle physical exam findings may include broad nasal root and long, narrow fingers and toes.

Davies discusses the mechanism and spectrum of immunodeficiency in 22q11 deletion syndrome. Due to abnormal development of the third and fourth pharyngeal pouches, immunodeficiency results from the subsequent abnormal development of the thymus. There is a highly variable range of presentation, which can include severe combined immunodeficiency when there is complete athymia.

Figure A shows a newborn with a cleft palate. Cleft palate is the classic facial defect associated with 22q11 deletion. Illustration A shows a schematic representation of 22q11 microdeletion.

Incorrect Answers:
Answer 1: This is the mechanism of Down's syndrome, which is the most common chromosomal disorder. Down's syndrome is classically associated with atrial septal defects.
Answer 2: This is the mechanism of Edward's syndrome, which classically presents with rocker-bottom feet and micrognathia.
Answer 3: This is the mechanism behind several disorders, including Huntington's disease, Friedreich's ataxia, and myotonic dystrophy.
Answer 5: This can be the mechanism behind Prader-Willi or Angelman's syndromes.

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