“Hereditary angioneurotic edema” is due to deficiency of:
**Core Concept**
Hereditary angioneurotic edema (HANE) is a rare genetic disorder characterized by recurrent episodes of severe swelling, particularly in the limbs, face, and airways. This condition is caused by a deficiency of a crucial enzyme involved in the regulation of the complement system.
**Why the Correct Answer is Right**
The correct answer is related to the deficiency of C1 esterase inhibitor (C1-INH), a protein that regulates the activity of the complement system, a group of proteins that play a key role in the immune response. C1-INH prevents the excessive activation of the complement system, which can lead to the release of histamine and other mediators that cause vascular permeability and edema. In HANE, the deficiency of C1-INH leads to the uncontrolled activation of the complement system, resulting in the characteristic symptoms of the disease.
**Why Each Wrong Option is Incorrect**
**Option A:** Factor XII deficiency is associated with a bleeding disorder, hemophilia, and is not directly related to HANE.
**Option B:** Prekallikrein deficiency is also associated with a bleeding disorder and is not the underlying cause of HANE.
**Option C:** Complement component 2 (C2) deficiency is another genetic disorder that affects the complement system, but it is not the primary cause of HANE.
**Clinical Pearl / High-Yield Fact**
C1 esterase inhibitor deficiency can be diagnosed through a combination of clinical history, laboratory tests (such as C1-INH levels and functional assays), and genetic testing. Treatment options for HANE include intravenous C1-INH replacement therapy and medications that inhibit the complement system, such as ecallantide and icatibant.
**Correct Answer:** C.