A 35-year-old man presents with progressive choreiform movements, psychiatric disturbances, and cognitive decline. His father had similar symptoms that began in his late 40s. Genetic testing would most likely reveal an abnormal expansion of which trinucleotide repeat?
✓ Correct Answer: Option D
This clinical presentation and autosomal dominant inheritance pattern are characteristic of Huntington's disease, which is caused by an abnormal expansion of CAG trinucleotide repeats in the huntingtin gene.