A 45-year-old patient presents with progressive chorea, psychiatric symptoms, and dementia. Family history reveals similar symptoms in the father and grandfather. The disorder is inherited in an autosomal dominant pattern and involves an expansion of CAG trinucleotide repeats. Which genetic disorder is most likely responsible?

The correct answer to the question "A 45-year-old patient presents with progressive chorea, psychiatric symptoms, and dementia. Family history reveals similar symptoms in the father and grandfather. The disorder is inherited in an autosomal dominant pattern and involves an expansion of CAG trinucleotide repeats. Which genetic disorder is most likely responsible?" is Option C: Huntington's disease.

The other options — A) Fragile X syndrome, B) Myotonic dystrophy, D) Friedreich's ataxia — are incorrect for this USMLE Exam Prep question. As explained above: Huntington's disease is an autosomal dominant neurodegenerative disorder caused by an expansion of CAG trinucleotide repeats in the HTT gene. It classically presents with chorea, psychiatric symptoms…