Immunodeficiencies Quiz: Ace Your Exams

A 2-year-old boy is brought to the emergency department for evaluation of a large abscess on his right arm. He was treated with oral antibiotics for two similar abscesses over the past year. Previously, these abscesses drained purulent material, and the cultures were positive for Staphylococcus aureus. The patient was hospitalized four months ago with pneumonia and associated empyema. The patient takes no medications and immunizations are up to date.  The patient’s brother died at the age of four months due to infection with Listeria monocytogenes. Temperature is 38.9 C° (102 F°), pulse is 90/min, respirations are 19/min and blood pressure is 100/60 mmHg. Physical examination demonstrates a 4x5 cm fluctuant mass with associated induration and erythema on the right arm. A dihydrorhodamine (DHR) 123 test demonstrates absence of fluorescence on flow cytometry. Which of the following best describes the etiology of this patient’s recurrent infections?