This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Medicine
[{'content': "Williams 'syndrome is an autosomal dominant disorder characterized by all of the following features, except: \nSelect and explain. \nA. Hypercalcemia, B. Mental retardation, C. Subvalvular aortic stenosis, D. Elfin facies", 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. C. Subvalvular aortic stenosisWilliam's syndrome or Idiopathic hypercalcemia of infancy is an autosomal dominant disorder characterized by multiple congenital developmental defects, including supravalvular aortic stenosis, mental retardation, and an elfin facies, in association with hypercalcemia due to abnormal sensitivity to vitamin D.", 'role': 'assistant'}]