A 2-year-old boy has severe eczema, recurrent pyogenic sinopulmonary infections, and repeated episodes of bleeding. Platelets are small and reduced in number. Serum shows low IgM with elevated IgA and IgE. Which gene mutation underlies this condition?

• A CYBB encoding gp91-phox of NADPH oxidase
• B WAS encoding a cytoskeletal regulator of hematopoietic cells ✓
• C RAG1 encoding the recombinase essential for V(D)J rearrangement
• D STAT3 encoding the signaling molecule downstream of IL-6 and IL-23 receptors

Explanation

Wiskott-Aldrich syndrome is an X-linked disorder caused by mutations in the WAS gene, whose product regulates actin polymerization in platelets and lymphocytes. The classic triad is eczema, thrombocytopenia with characteristically small platelets, and recurrent infections, with the distinctive immunoglobulin pattern of low IgM and raised IgA and IgE. Option A gives chronic granulomatous disease with normal platelets, option C gives Omenn syndrome or SCID with absent T and B cells, and option D gives hyper-IgE syndrome, none of which feature thrombocytopenia.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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