**Core Concept**
Hereditary angioneurotic edema (HAE) is a rare, autosomal dominant disorder characterized by recurrent episodes of severe swelling, typically affecting the face, extremities, and airways. This condition is caused by a deficiency or dysfunction of a specific enzyme involved in the regulation of the complement system.

**Why the Correct Answer is Right**
The correct answer is due to the deficiency of C1 esterase inhibitor (C1-INH), a critical regulator of the complement system and the contact system. C1-INH prevents the uncontrolled activation of the complement system, which leads to the excessive production of bradykinin, a potent vasodilator. Without sufficient C1-INH, the levels of bradykinin increase, causing blood vessels to dilate and leading to the characteristic edema seen in HAE.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the underlying cause of HAE. While the complement system is involved, it is not the primary defect.
**Option B:** This option is incorrect because it is a characteristic symptom of HAE, not the underlying cause.
**Option C:** This option is incorrect because it is not directly related to the pathophysiology of HAE.

**Clinical Pearl / High-Yield Fact**
HAE can be triggered by various factors, including stress, trauma, and certain medications, highlighting the importance of a thorough medical history in diagnosing this condition.

**Correct Answer: C. Deficiency of C1 esterase inhibitor.**