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: Pathology
[{'content': 'In Huntington chorea the causative mutation in the protein huntingtin is a: \nSelect and explain. \nA. Point mutation, B. Gene deletion, C. Frameshift mutation, D. Trinucleotide repeat expansion', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Huntington disease (HD) Mutation in the HTT gene which codes for protein called huntingtin which is impoant to neurons. The HTT mutation involves a DNA segment known as a CAG trinucleotide repeat. Made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row leading to the disease.', 'role': 'assistant'}]