A 9-month-old boy was suspected of having an immune deficiency because he had many recurrent infections with Streptococcus pneumoniae.Laboratory tests revealed a normal percentage of T cells and T-cell subsets but a lack of mature B cells and immunoglobulins.This boy most likely has:

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X-linked agammaglobulinemia is a primary immunodeficiency disorder caused by a mutation in the Bruton's tyrosine kinase (BTK) gene, leading to a lack of mature B cells and immunoglobulins. Recurrent infections with encapsulated bacteria, such as Streptococcus pneumoniae, are common in patients with X-linked agammaglobulinemia. The normal percentage of T cells and T-cell subsets in this case rules out Wiskott-Aldrich syndrome and DiGeorge syndrome, which are associated with T-cell abnormalities. Chronic granulomatous disease is also unlikely since it is characterized by recurrent bacterial and fungal infections caused by a defect in phagocytic immune cells, and the presentation described in the case suggests an impaired humoral immune response rather than a defect in phagocytosis.

A 9-Month-Old Boy Was Suspected of Having an Immune Deficiency