A 7-Month-Old Boy Is Evaluated in the Clinic for Recurrent

A 7-month-old boy is evaluated in the clinic for recurrent bacterial infections. His tonsils are not visible on physical examination. Serum immunoglobulin A (IgA) and IgG levels are markedly decreased, and serum IgM levels are slightly below normal. Careful examination of this infant reveals white plaques along the buccal mucosa, palate, and tongue, consistent with oral candidiasis (thrush) . Analysis of blood cells reveals normal numbers of B cells and very few CD3⁺ cells. In addition, maternally-derived T cells, as determined by HLA typing, are detectable. The infant's mother reports that two of her three brothers died of infection as young children. Collectively, this presentation and history are most consistent with which of the following disorders?

A) X-linked agammaglobulinemia
B) X-linked severe combined immunodeficiency disease (X-linked SCID)
C) Common variable immunodeficiency
D) X-linked hyper-IgM syndrome
E) Adenosine deaminase deficiency (ADA)