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.Based on the findings described,which one of the following should be excluded from the differential diagnosis?

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Quizplus · Accepted Answer

The infant's presentation suggests an underlying congenital immunodeficiency.X-linked hyper-IgM syndrome is characterized by failure of the B cell heavy chain to undergo switching from the IgM isotype,excess levels of IgM antibody (hyper-IgM)are often detectable in sera from patients.Thus,these patients are predisposed to both pyogenic and protozoal infections.X-linked severe combined immunodeficiency disease (SCID)and adenosine deaminase (ADA)deficiency are both forms of SCID and will present as very low levels of T cell-dependent Ig isotypes (IgG and IgA),as well as defects in cell-mediated immunity.X-linked agammaglobulinemia is a defect in B cell maturation and will present as very low levels of all antibody isotypes.Common variable immunodeficiency includes a number of defects in B cell differentiation into antibody-secreting cells and may present as pan-Ig deficiency.

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