Features of X-linked agammaglobulinemia: which immunoglobulins are reduced and typical age of presentation?

• A. Absence of B cells with markedly reduced all immunoglobulins; presents in infancy with recurrent bacterial infections; treated with IVIG.
• B. Overproduction of immunoglobulins causing autoimmune disease.
• C. T-cell deficiency with normal B cells.
• D. Normal immunoglobulins but decreased light chains.

Answer: (A)

X-linked agammaglobulinemia occurs when B cell development is blocked, usually due to a BTK gene defect. Because mature B cells fail to form, there are essentially no B cells in the blood and no plasma cells to produce antibodies, so all immunoglobulin levels (IgG, IgA, IgM) are markedly reduced. Clinically, this becomes evident after maternal IgG wanes, typically in infancy around 6 months to a couple of years, with recurrent bacterial infections of the sinopulmonary tract and ears. Management centers on replacing antibodies with intravenous immunoglobulin to reduce infection risk.

This best fits because it describes absence of B cells, pan-hypogammaglobulinemia, infantile presentation, and the use of IVIG. The other choices describe scenarios that don’t match X-linked agammaglobulinemia—such as immunoglobulin overproduction with autoimmunity, T-cell–dominant deficiency with normal B cells, or normal immunoglobulins with decreased light chains—which don’t reflect the B cell–driven lack of antibodies seen in this condition.