A 6-month-old infant develops recurrent bacterial infections, absent lymph nodes on examination, and laboratory findings show very low or absent B cells but normal T cell numbers and T cell function. Immunoglobulin levels are undetectable. This presentation is most consistent with:
- A X-linked severe combined immunodeficiency (X-SCID)
- B X-linked agammaglobulinemia (Bruton's disease) ✓
- C Common variable immunodeficiency (CVID)
- D DiGeorge syndrome
Explanation
X-linked agammaglobulinemia (XLA, Bruton's disease) presents in male infants at 6–9 months (after maternal IgG wanes) with recurrent bacterial infections, absent/very low B cells, profound hypogammaglobulinemia, but intact T cell numbers and function. It is caused by a mutation in Bruton's tyrosine kinase (BTK), which is essential for B cell maturation from pre-B to mature B cells. X-SCID has absent T and NK cells with B cells present but non-functional; CVID presents later (second/third decade) with normal B cell numbers but impaired antibody production; DiGeorge affects T cells (thymic aplasia) not 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.