Which statement best describes the inheritance pattern of myotonic dystrophy type 1?

Which statement best describes the inheritance pattern of myotonic dystrophy type 1?

• A. Autosomal recessive
• B. Mitochondrial inheritance
• C. Autosomal dominant with anticipation due to repeat expansion
• D. X-linked recessive

Answer: (C)

Autosomal dominant inheritance with anticipation due to trinucleotide repeat expansion explains myotonic dystrophy type 1. The disease is caused by a CTG repeat expansion in the DMPK gene, and the number of repeats tends to increase in successive generations. This expansion leads to earlier onset and more severe disease in children compared to their parents, which is the hallmark of anticipation. Because only one mutated copy is enough to cause disease, each child of an affected parent has about a 50% chance of inheriting the condition, and both sexes are affected equally. It is not inherited via mitochondria, nor is it X-linked or autosomal recessive.

Autosomal dominant inheritance with anticipation due to trinucleotide repeat expansion explains myotonic dystrophy type 1. The disease is caused by a CTG repeat expansion in the DMPK gene, and the number of repeats tends to increase in successive generations. This expansion leads to earlier onset and more severe disease in children compared to their parents, which is the hallmark of anticipation. Because only one mutated copy is enough to cause disease, each child of an affected parent has about a 50% chance of inheriting the condition, and both sexes are affected equally. It is not inherited via mitochondria, nor is it X-linked or autosomal recessive.