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Huntington's disease (HD) is a progressive and hereditary neurological disorder caused by a genetic mutation in the HTT gene, which leads to the production of an abnormal version of the huntingtin protein. This mutation involves the expansion of a CAG trinucleotide repeat in the gene. The disease is inherited in an autosomal dominant pattern, meaning that having just one copy of the mutated gene from an affected parent is enough to cause the disorder. Symptoms typically begin in mid-adulthood, around the ages of 30 to 50, and include a range of motor, cognitive, and psychiatric disturbances. Motor symptoms often start with slight involuntary movements (chorea), which progress to more pronounced movement problems, while cognitive decline gradually leads to dementia. Psychiatric symptoms can include depression, irritability, and mood swings. The number of CAG repeats is inversely correlated with the age of onset; more repeats can lead to an earlier onset of symptoms. Currently, there is no cure for Huntington's disease, and treatments focus on managing symptoms to improve quality of life. Problem: What type of genetic mutation causes Huntington's disease? A) Duplication mutation B) Nonsense mutation C) Trinucleotide repeat expansion D) Missense mutation
