A 6-year-old child develops recurrent sino-pulmonary infections caused by encapsulated bacteria. IgG, IgA and IgM levels are all markedly reduced, and circulating B-lymphocytes are absent on flow cytometry. The underlying molecular defect most likely involves which gene product?
- A Common gamma chain (γc)
- B ADA (adenosine deaminase)
- C Bruton's tyrosine kinase (BTK) ✓
- D RAG-1 recombinase
Correct answer: C. Bruton's tyrosine kinase (BTK)
Explanation
Absence of all serum immunoglobulins and circulating B-cells with normal T-cell counts is the hallmark of X-linked agammaglobulinemia (XLA), caused by a defect in Bruton's tyrosine kinase essential for pre-B-cell maturation. Common gamma chain deficiency causes X-linked SCID with absent T and NK cells. ADA deficiency causes autosomal SCID. RAG-1 defects also cause SCID but T-cells are equally absent.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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