This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
[{'content': 'A 38-year-old man presents with involuntary facial grimacing, shrugging of the shoulders, and jerking movements of the limb. His father was similarly affected. There is also a history of mood changes for the past 3 months. On examination, he appears restless with intermittent slow movements of his hands and face. He has difficulty performing rapid finger movements, and tone is decreased in the upper and lower limbs. Which of the following is most likely to represent the progression of his illness? \nSelect and explain. \nA. a normal life span, B. a 50% chance of only male children being similarly affected, C. mental deterioration, D. eventual development of rigidity', 'role': 'user'}, {'content': "Answer: C \nExplanation: This is a case of Huntington's chorea. It is an autosomal dominant gene (found on the short arm of chromosome 4), and male and female children are equally affected. Movement disorder, mental deterioration, and personality change are the hallmarks of the disease, but can be very subtle initially. The disease starts typically between ages 35 and 40 (although the variation is wide) and runs its course in about 15 years. The akinetic rigid variety (Westphal variant) of Huntington's typically has a childhood onset.", 'role': 'assistant'}]