This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Hereditary angioneurotic edema is due to - 
Select and explain. 
A. Deficiency of C1 inhibitor, B. Deficiency of NADPH oxidase, C. Deficiency of MPO, D. Deficiency of properdin
A: Deficiency of C1 inhibitor
Answer: A: Deficiency of C1 inhibitor 
Explanation: The deficiency of C1 inhibitor is associated with hereditary angioneurotic edema. It is a condition characterised by episodic angioedema of the subcutaneous tissues or of the mucosa of the respiratory or alimentary tracts. Fatal if larynx or trachea affected. Attack is precipitated by local exhaustion of the reduced amount of the C1 inhibitor present ,leading to the autocatalytic activation of C1 and unrestrained breakdown of C4 and C2. Reference : Anathanarayan & paniker's 9th edition, pg no: 126 <\p>