Most common cause of chronic granulomatous disease in children is:
**Core Concept**
Chronic granulomatous disease (CGD) is a rare genetic disorder characterized by the inability of phagocytic cells to kill certain bacteria and fungi, leading to recurrent life-threatening infections. This condition is caused by mutations in the genes encoding subunits of the enzyme NADPH oxidase, which is essential for the production of superoxides that kill ingested microbes.
**Why the Correct Answer is Right**
The most common cause of CGD in children is a mutation in the CYBB gene, which encodes the gp91 phox subunit of NADPH oxidase. This mutation leads to a deficiency in the production of superoxides, making phagocytic cells unable to kill catalase-positive bacteria such as Staphylococcus aureus and Aspergillus species. The X-linked recessive inheritance pattern of CGD means that the disease primarily affects males, who have only one X chromosome.
**Why Each Wrong Option is Incorrect**
* **Option A:** Not specified, but it's essential to know that CGD is not caused by a deficiency in the CYBA gene, which encodes the p22 phox subunit of NADPH oxidase.
* **Option B:** Not specified, but it's crucial to understand that CGD is not caused by a mutation in the NCF1 gene, which encodes the p47 phox subunit of NADPH oxidase.
* **Option D:** Not specified, but it's vital to recognize that CGD is not caused by a deficiency in the NOX2 gene, which encodes the gp91 phox subunit of NADPH oxidase, but rather a mutation in this gene.
**Clinical Pearl / High-Yield Fact**
The clinical presentation of CGD typically includes recurrent infections with catalase-positive bacteria and fungi, such as abscesses, pneumonia, and osteomyelitis. A key diagnostic clue is the presence of granulomas in affected tissues, which are a hallmark of the chronic inflammatory response in CGD.
**Correct Answer: C.**