Chromosomal abnormalities · USMLE Step 1

A newborn with congenital heart disease and thymic aplasia is diagnosed with 22q11 deletion. Which mechanism caused this abnormality?

  1. Uniparental disomy of chromosome 22
  2. Microdeletion via non-allelic homologous recombination
  3. Balanced reciprocal translocation event
  4. Isochromosome formation of chromosome 22
Show answer and explanation

Correct answer: Microdeletion via non-allelic homologous recombination

22q11 deletions often occur due to non-allelic homologous recombination, causing microdeletions. This leads to DiGeorge syndrome features such as thymic aplasia. Uniparental disomy does not cause this syndrome.

Difficulty: Medium Question 7 of 20

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