Which muscular dystrophy is characterized by myotonia and progressive weakness with autosomal dominant inheritance?

• A. Facioscapulohumeral muscular dystrophy
• B. Pompe disease
• C. Myotonic dystrophy type 1
• D. Duchenne muscular dystrophy

Answer: (C)

Myotonia with progressive weakness that follows an autosomal dominant pattern points to myotonic dystrophy type 1. Myotonia means a delayed ability of muscles to relax after contraction, which is a hallmark feature of this condition. The autosomal dominant inheritance means that only one mutated gene copy is needed to cause the disease, so it can pass from an affected parent to half of the offspring. Pompe disease and Duchenne muscular dystrophy don’t typically feature myotonia; Pompe is autosomal recessive and mainly presents with early-onset muscle weakness and cardiomyopathy, while Duchenne is X-linked and driven by dystrophin loss. Facioscapulohumeral dystrophy is autosomal dominant and causes scapulohumeral weakness, but myotonia isn’t a defining feature.