A patient with recurrent sino-pulmonary infections and absent serum immunoglobulins has normal T lymphocyte numbers but no B cells in peripheral blood. Which gene is mutated in this condition?

• A ADA (adenosine deaminase)
• B RAG-1/RAG-2
• C IL-2 receptor gamma chain (common gamma chain)
• D BTK (Bruton's tyrosine kinase) ✓

Explanation

Bruton's X-linked agammaglobulinemia results from a mutation in BTK, a tyrosine kinase required for B cell maturation from pre-B to mature B cell stage. This causes complete absence of peripheral B cells and all immunoglobulin classes, while T cell numbers and function remain normal. Boys present after 6 months when maternal IgG wanes, with recurrent bacterial infections. ADA deficiency and RAG mutations cause combined immunodeficiency affecting both B and T cells, and IL-2Rγ chain mutation 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.