A child presents with recurrent pyogenic infections, absent lymph nodes and tonsils, markedly reduced serum immunoglobulin levels, and near-absent B cells on flow cytometry. Bone marrow shows normal pro-B cells but no pre-B cells onward. The defective enzyme/protein most likely responsible is:
- A Bruton's tyrosine kinase (BTK) ✓
- B Adenosine deaminase (ADA)
- C CD40 ligand (CD154)
- D Common gamma-chain (γc, IL-2Rγ)
Correct answer: A. Bruton's tyrosine kinase (BTK)
Explanation
X-linked agammaglobulinemia (Bruton's disease) results from BTK deficiency, which blocks B-cell maturation at the pro-B to pre-B cell transition. All downstream B-cell populations and immunoglobulin classes are absent. ADA deficiency causes SCID (T+B cells absent); CD40L deficiency causes Hyper-IgM syndrome; γc deficiency causes X-linked SCID.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.