Immunology USMLE Step 1 Practice Question
A 9 month old boy is brought to the clinic for recurrent otitis media, sinus infections, and bacterial pneumonia after weaning from breastfeeding. He has had chronic diarrhea with Giardia as well. Examination shows absent tonsils and no palpable lymph nodes. Serum studies show very low levels of all immunoglobulin classes and absent circulating mature B cells. Which of the following is the most likely underlying defect?
Answer choices
- ADeletion of chromosome 22q11 causing thymic aplasia
- BDefect in CD40 ligand causing inability to class switch
- CMutation in WAS gene causing cytoskeletal dysfunction
- DDeficiency of adenosine deaminase causing toxic purine metabolite accumulation
- EMutation in Bruton's tyrosine kinase causing failure of B cell maturationCorrect answer
- FGamma chain (γc) mutation causing X-linked SCID
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