A 10-year-old boy with a history of recurrent bacterial infections presents with fever and a productive cough. Biochemical analysis of his neutrophils demonstrates defective oxidative burst. This patient most likely has inherited mutations in the gene that encodes which of the following proteins?

**Core Concept**
The patient's condition is characterized by recurrent bacterial infections and a defective oxidative burst in neutrophils, indicating a problem with the immune system's ability to kill pathogens. This is a classic presentation of Chronic Granulomatous Disease (CGD), a genetic disorder caused by mutations in the genes encoding subunits of the enzyme NADPH oxidase.

**Why the Correct Answer is Right**
The defective oxidative burst in neutrophils is due to the impaired production of reactive oxygen species (ROS), which are essential for killing ingested bacteria. NADPH oxidase is the enzyme responsible for generating ROS in neutrophils. The gene that encodes the gp91phox subunit of NADPH oxidase is CYBB, while the gene that encodes the p22phox subunit is CYBA. Mutations in these genes lead to the production of abnormal NADPH oxidase subunits, resulting in the defective oxidative burst seen in CGD.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the defective oxidative burst in neutrophils.
**Option B:** The gene that encodes the p47phox subunit of NADPH oxidase is NCF1, which is not the correct answer.
**Option D:** The gene that encodes the p67phox subunit of NADPH oxidase is NCF2, which is not the correct answer.

**Clinical Pearl / High-Yield Fact**
Chronic Granulomatous Disease is a rare genetic disorder that affects approximately 1 in 250,000 individuals worldwide. It is characterized by recurrent bacterial and fungal infections, and a distinctive clinical presentation that includes lymphadenopathy, hepatosplenomegaly, and granulomatous inflammation in affected organs.

**Correct Answer:** C.

✓ Correct Answer: D. NADPH oxidase