A 6-year-old boy with recurrent sinopulmonary infections is found to have normal B-cell counts but absent serum immunoglobulins of all isotypes. His T-cell count and function are normal. Genetic testing reveals a mutation causing inability to signal downstream of the pre-B cell receptor. Which kinase is most likely deficient?
- A ZAP-70
- B JAK3
- C Bruton's tyrosine kinase (Btk) ✓
- D Adenosine deaminase
Correct answer: C. Bruton's tyrosine kinase (Btk)
Explanation
X-linked agammaglobulinaemia (XLA) is caused by a mutation in Bruton's tyrosine kinase (Btk), which is essential for pre-B cell receptor signalling and subsequent B-cell maturation. Affected boys have virtually absent serum immunoglobulins and absent mature B cells in peripheral blood, while T cells remain normal. ZAP-70 deficiency causes selective CD8+ T-cell deficiency; JAK3 and ADA deficiencies cause SCID with combined T and B cell loss.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.