In an evaluation of an 8-year-old boy who has had recurrent infections since the first year of life, findings include enlargement of the liver and spleen, lymph node inflammation, and a superficial dermatitis resembling eczema. Microscopic examination of a series of peripheral blood smears taken during the course of a staphylococcal infection indicates that the bactericidal capacity of the boy’s neutrophils is impaired or absent. What is the most likely cause of this child’s illness?

**Core Concept**
The child's symptoms suggest a primary immunodeficiency disorder affecting the neutrophil function, leading to recurrent infections and impaired bactericidal capacity. This condition is characterized by the absence or dysfunction of a key component of the neutrophil's oxidative burst machinery, which is essential for killing ingested microbes.

**Why the Correct Answer is Right**
The impaired neutrophil function is due to a deficiency in the enzyme neutrophil NADPH oxidase, which is responsible for generating superoxides and other reactive oxygen species necessary for killing bacteria. This enzyme is a multi-subunit complex, with the most critical component being the gp91-phox subunit, which is encoded by the CYBB gene. The absence or dysfunction of this enzyme leads to chronic granulomatous disease (CGD), characterized by recurrent infections with catalase-positive bacteria, such as Staphylococcus aureus, and impaired bactericidal capacity of neutrophils.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically address the impaired neutrophil function and recurrent infections seen in this child. While chronic granulomatous disease is a primary immunodeficiency disorder, other conditions like severe combined immunodeficiency (SCID) or common variable immunodeficiency (CVID) may present with different clinical features.

**Option B:** This option is incorrect because it refers to a different type of immunodeficiency disorder, namely, chronic granulomatous disease with an autosomal recessive inheritance pattern. While the clinical features may be similar, the genetic basis and inheritance pattern differ.

**Option C:** This option is incorrect because it is not directly related to the child's symptoms or the impaired neutrophil function. While infections can occur in the absence of a functioning spleen, the child's symptoms suggest a primary immunodeficiency disorder affecting the neutrophil function.

**Option D:** This option is incorrect because it is not a recognized primary immunodeficiency disorder affecting the neutrophil function.

**Clinical Pearl / High-Yield Fact**
Chronic granulomatous disease (CGD) is characterized by recurrent infections with catalase-positive bacteria, and the diagnosis can be confirmed by the nitroblue tetrazolium (NBT) test, which assesses the ability of neutrophils to generate superoxides.

**Correct Answer:** C.

✓ Correct Answer: A. Defect in the enzyme NADPH oxidase