18-month-old boy is brought to the emergency department due to blood in his stool, which the parents noticed
when changing his diaper. The infant has had no previous bleeding and has been eating and drinking normally.
He has a history of recurrent otitis media, frequent herpes labialis, and 2 episodes of pneumonia. Vital signs are
normal. On examination, the patient is well developed, well nourished, and has a fair complexion. He has eczema
on his cheeks, trunk, and extremities. Scattered petechiae are also visible on his lower extremities. The
remainder of the physical examination is unremarkable. Laboratory studies show a platelet count of 24,000/mm3
and a leukocyte count of 9,000/mm3. Peripheral smear confirms the low platelet count and that the platelets are
small. Genetic testing confirms the diagnosis. Which of the following processes is most likely affected by this
patient’ s gene mutation?
- 0 A. Antibody class switching
- 0 B. Cytoskeleton regulation
- 0 C. DNA repair
- 0 D. Hydrogen peroxide production
- 0 E. Maturation of T cells
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