Immunology USMLE Step 1 Practice Question
A 14-month-old boy presents to the emergency department with bloody diarrhea and diffuse eczema. Parents report recurrent otitis media since infancy and note he bruises easily. Vital signs show HR 118/min, BP 95/58 mmHg, temp 37.2°C. Examination reveals petechiae, excoriated flexural plaques, and hepatosplenomegaly. Laboratory studies show thrombocytopenia (platelets 28,000/μL) with microcytic morphology. Peripheral blood smear confirms small platelet size. No lymphadenopathy is palpated. Which genetic disorder best explains this clinical triad?
Answer choices
- ADeficiency of CD40 ligand causing inability to class switch
- BMutation in BTK causing absent mature B cells
- CDeficiency of C1 esterase inhibitor causing recurrent edema
- DDeficiency of adenosine deaminase causing severe combined immunodeficiency
- EMutation in WAS gene causing defective actin cytoskeleton reorganizationCorrect answer
- FDOCK8 deficiency causing combined immunodeficiency with eczema
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