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': 'Myotonic dystrophy: \nSelect and explain. \nA. CTG trinucleotide repeats, B. Dystrophin 1, C. Dystrophin 2, D. CAG repeats', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. A. CTG trinucleotide repeatsExplanationMyotonic dystrophy is an autosomal dominant multisystem disorder associated with skeletal muscle weakness, cataracts, endocrinopathy, and cardiomyopathy. The disease is caused by expansions of CTG triplet repeats in the 3'-noncoding region of the myotonic dystrophy protein kinase (DMPK) gene.", 'role': 'assistant'}]