Chronic granulomatous disease is due to deficiency of
**Core Concept**
Chronic granulomatous disease (CGD) is a rare genetic disorder characterized by recurrent life-threatening infections, particularly with catalase-positive bacteria and fungi. It results from a defect in the production of reactive oxygen species (ROS) by phagocytes, leading to impaired bacterial killing.
**Why the Correct Answer is Right**
CGD is caused by mutations in the genes encoding the subunits of the NADPH oxidase complex, which is essential for the production of superoxide (O2-) and subsequent ROS. The NADPH oxidase complex is composed of two membrane-bound subunits (gp91phox and p22phox) and three cytosolic subunits (p47phox, p67phox, and p40phox). A deficiency in any of these subunits impairs the production of ROS, leading to the characteristic features of CGD. The most common mutations affect the CYBB gene, which encodes the gp91phox subunit.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CGD is not caused by a deficiency in the enzyme NADPH.
**Option B:** This option is incorrect because CGD is not caused by a deficiency in the enzyme myeloperoxidase, which is involved in the production of hypochlorous acid.
**Option C:** This option is incorrect because CGD is not caused by a deficiency in the enzyme lysozyme, which is involved in the breakdown of bacterial cell walls.
**Option D:** This option is incorrect because CGD is not caused by a deficiency in the enzyme lactoferrin, which is involved in the sequestration of iron.
**Clinical Pearl / High-Yield Fact**
Patients with CGD are at increased risk of developing granulomatous lesions, particularly in the lungs and lymph nodes, due to the impaired ability of phagocytes to kill bacteria and fungi. This can lead to complications such as pneumatoceles and pneumothoraces.
**Correct Answer:** C. Deficiency of the NADPH oxidase complex.