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Immunology · NEET PG Preparation Microbiology

A 32-year-old man presents with recurrent sinopulmonary infections and bronchiectasis. Laboratory evaluation reveals profoundly low serum levels of I…

Practice question from Immunology (NEET PG Preparation Microbiology), with the correct answer and a step-by-step solution.

medium · MCQ · Q-EAAC1E

A 32-year-old man presents with recurrent sinopulmonary infections and bronchiectasis. Laboratory evaluation reveals profoundly low serum levels of IgG, IgA, and IgM, while circulating CD19+ and CD20+ B lymphocytes are present in normal numbers. T-lymphocyte counts and functions are normal. Which of the following is the most likely molecular defect responsible for this condition?

  1. A.Mutation in the Bruton tyrosine kinase (BTK) gene
  2. B.Mutation in the CD40 ligand (CD40L) gene
  3. C.Mutation in the AICDA gene encoding activation-induced cytidine deaminase
  4. D.Mutation in the TACI (TNFRSF13B) geneCorrect answer

Solution

This patient has Common Variable Immunodeficiency (CVID), characterized by hypogammaglobulinemia, normal or near-normal numbers of B cells, and recurrent infections. Mutations in TACI (TNFRSF13B), BAFF receptor, or CD19 are implicated in CVID. BTK deficiency causes X-linked agammaglobulinemia where circulating B cells are absent. CD40L deficiency causes X-linked hyper-IgM syndrome. AICDA mutations cause autosomal recessive hyper-IgM syndrome.

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