This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'An 18-year-old woman comes to the emergency room with recurrent facial edema, especially around her lips. She also has recurrent bouts of intense abdominal pain and cramps, sometimes associated with vomiting. Laboratory examination reveals decreased C4, while levels of C3, decay-accelerating factor, and IgE are within normal limits. A deficiency of which of the following substances is most likely to be associated with these findings? \nSelect and explain. \nA. C1 esterase inhibitor, B. Complement components C3 and C5, C. Decay-accelerating factor, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: This\xa0 women is suffering from hereditary angioedema.\nC1 inhibitor blocks the activation of C1, the first protein of the classical complement pathway. Inherited deficiency of this inhibitor is the cause of hereditary angioedema.\nDeficiency of decay accelerating factor (DAF), which breaks down the C3 convertase complex, is seen in paroxysmal nocturnal hemoglobinuria (PNH).\nReference-Robbins BASIC PATHOLOGY 10th edition pg- 77', 'role': 'assistant'}]