A 2-year-old boy has recurrent pyogenic infections, severe atopic eczema, and recurrent epistaxis. Platelet count is 45,000/uL with small platelets on smear. Serum IgM is low while IgA and IgE are elevated. Which gene mutation is responsible?
- A BTK gene encoding Bruton tyrosine kinase
- B WAS gene encoding WASp, involved in actin cytoskeletal reorganisation ✓
- C STAT3 gene encoding signal transducer downstream of IL-6 and IL-23
- D CYBB gene encoding gp91phox of NADPH oxidase
Correct answer: B. WAS gene encoding WASp, involved in actin cytoskeletal reorganisation
Explanation
The triad of eczema, thrombocytopenia with small platelets, and recurrent infections defines Wiskott-Aldrich syndrome, caused by mutations in the WAS gene on the X chromosome. The characteristic immunoglobulin pattern is low IgM with raised IgA and IgE. BTK mutation gives agammaglobulinemia without thrombocytopenia, STAT3 mutation gives Job syndrome with coarse facies and cold abscesses, and CYBB mutation gives chronic granulomatous disease with normal platelets.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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