A male infant with recurrent infections and virtual lack of gamma globulins, but normal T cell numbers and function, most likely has which condition?

• A. Combined immunodeficiency
• B. DiGeorge syndrome
• C. Iatrogenic immunodeficiency
• D. X-linked agammaglobulinemia

Answer: (D)

A pattern of normal T-cell numbers and function with a near absence of immunoglobulins points to an isolated B-cell maturation/antibody deficiency. This fits X-linked agammaglobulinemia, caused by a mutation in BTK that blocks B-cell development. Without mature B cells, there are very few immunoglobulins (gamma globulins) in circulation, leading to recurrent bacterial infections in infancy as maternal antibodies wane. T-cell–mediated immunity remains intact, so cellular immunity is preserved.

This contrasts with combined immunodeficiency, where both B and T cell functions are impaired; with DiGeorge syndrome, the hallmark is reduced T cells due to thymic aplasia; and iatrogenic immunodeficiency arises from external causes like treatment rather than a congenital B-cell defect.