A 6-year-old boy is being evaluated in the office due to a history of recurrent infections and failure to thrive. He has been hospitalized for pneumococcal pneumonia twice and has had 5 episodes of otitis media. The patient also has a history of prolonged diarrhea caused by Giardia intestinalis. Physical examination shows a lack of tonsillar tissue, as well as minimally palpable cervical, axillary, and inguinal lymph nodes. Further evaluation shows that the patient has defective signaling between activated CD4 T cells and B cells. Which of the following laboratory findings are most likely to be found in this patient?

Question

A 6-year-old boy is being evaluated in the office due to a history of recurrent infections and failure to thrive.  He has been hospitalized for pneumococcal pneumonia twice and has had 5 episodes of otitis media.  The patient also has a history of prolonged diarrhea caused by Giardia intestinalis.  Physical examination shows a lack of tonsillar tissue, as well as minimally palpable cervical, axillary, and inguinal lymph nodes.  Further evaluation shows that the patient has defective signaling between activated CD4 T cells and B cells.  Which of the following laboratory findings are most likely to be found in this patient?

Quizplus · Accepted Answer

Eductional Objective: Hyper-IgM syndrome is usually caused by a defect in CD40 ligand, which prevents B cells from undergoing class-switch recombination.  Clinical features include recurrent sinopulmonary, gastrointestinal (eg, Giardia), and opportunistic infections.  Laboratory findings include elevated IgM and low or absent IgG, IgA, and IgE.

A 6-Year-Old Boy Is Being Evaluated in the Office Due