What pattern of inheritance is typical for DM1?

• A. Autosomal dominant with anticipation
• B. Autosomal recessive
• C. X-linked
• D. Mitochondrial

Answer: (A)

Myotonic Dystrophy type 1 is inherited in an autosomal dominant pattern and shows anticipation because the disease is caused by a CTG trinucleotide repeat expansion in the DMPK gene. In autosomal dominant conditions, one mutated copy is enough to cause disease, and DM1 often appears in multiple generations. The twist here is anticipation: the CTG repeat length can increase when transmitted to the next generation, leading to earlier onset and typically more severe symptoms in children. That dynamic mutation explains why DM1 is described as autosomal dominant with anticipation. It’s not inherited in a recessive, X-linked, or mitochondrial fashion, since the transmission pattern aligns with a single-mutant-allele inheritance and the expansion-driven worsening across generations.