**Question:** NADPH oxidase deficiency causes:

**Core Concept:** NADPH oxidase is an enzyme complex responsible for producing reactive oxygen species (ROS) in phagocytes, which are essential for the immune response against foreign pathogens. In the absence or dysfunction of NADPH oxidase, ROS production is impaired, leading to compromised immune function.

**Why the Correct Answer is Right:**

NADPH oxidase deficiency mainly refers to the impairment in any of the subunits of the NADPH oxidase enzyme complex. The correct answer, **D**. Chronic granulomatous disease (CGD), is a rare genetic disorder caused by mutations in genes encoding for NADPH oxidase subunits. This leads to impaired ROS production, making the immune system unable to effectively combat pathogens.

**Why Each Wrong Option is Incorrect:**

A. Hypersensitivity reactions are a response to allergens and not a result of NADPH oxidase deficiency.

B. Acquired deficiency of NADPH oxidase is not a consequence of the enzyme complex's dysfunction, but rather due to other factors like drugs or infections.

C. Chronic granulomatous disease (CGD) is the correct answer, but it is the consequence, not the cause, of impaired NADPH oxidase function.

**Clinical Pearl / High-Yield Fact:**

CGD presents with recurrent life-threatening infections, granulomas, and a high risk of malignancies. Early diagnosis and appropriate treatment can improve the prognosis for patients with CGD.