A child with recurrent sinopulmonary infections is found to have absent tonsils, no palpable lymph nodes, and serum IgG <100 mg/dL with absent IgA and IgM. Peripheral blood lymphocytes show no CD19+ cells. Which gene mutation is most likely?
- A Common gamma chain (γc, IL2RG)
- B BTK (Bruton's tyrosine kinase) ✓
- C ADA (adenosine deaminase)
- D WASP (Wiskott-Aldrich syndrome protein)
Correct answer: B. BTK (Bruton's tyrosine kinase)
Explanation
X-linked agammaglobulinemia (XLA) results from BTK mutations causing a block at the pre-B cell stage; patients have no mature B cells (absent CD19+), negligible all immunoglobulin classes, absent tonsils/lymph nodes, and are susceptible to encapsulated bacteria and enteroviruses. Common gamma chain mutations cause X-linked SCID affecting T, B, and NK cells. ADA deficiency causes autosomal recessive SCID with absent lymphocytes. Wiskott-Aldrich shows thrombocytopenia, eczema, and combined immunodeficiency with present B cells.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.