A 13-month-old boy is admitted to the hospital due to diarrhea and dehydration. Over the past week, the patient has developed severe, watery diarrhea and has had poor oral intake. Medical history includes multiple episodes of bronchiolitis and, at age 8 months, an intensive care unit admission due to pneumococcal pneumonia requiring a brief period of mechanical intubation and chest tube placement. The parents say that he has been growing poorly over the past 6 months despite feeding well and supplemention with high-calorie formulas. On examination, the patient appears lethargic with sunken eyes and poor skin turgor, as well as moderate tachycardia and tachypnea. As part of the laboratory evaluation, flow cytometry of in vitro-stimulated CD4⁺ T cells reveals a near absence of CD40 ligand. Which of the following additional findings is most likely associated with this patient's condition?

Question

Quizplus · Accepted Answer

Eductional Objective: Hyper-IgM syndrome presents with recurrent sinopulmonary and gastrointestinal infections due to the absence of CD40 ligand on CD4⁺ T cells. Lack of interaction between CD40L and CD40 on B cells prevents the development of secondary germinal centers and impairs B-cell activation and immunoglobulin class switching.

A 13-Month-Old Boy Is Admitted to the Hospital Due to Diarrhea