Myotonic dystrophy (DM) is the most common form of myotonic myopathy, with an estimated prevalence of 1 in 7,000 people, though milder cases often go undiagnosed.
Overview
This multisystem disorder is inherited as an autosomal dominant trait and can affect various systems, including:
- Skeletal and smooth muscle
- Eyes
- Heart
- Endocrine system
- Central nervous system
The clinical spectrum ranges from mild to very severe, categorized into three overlapping phenotypes:
- Mild
- Classic
- Congenital
Genetic Basis of Myotonic Dystrophy
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Myotonic Dystrophy Type 1 (DM1)
- Cause: CTG trinucleotide expansion in the untranslated region of the DMPK gene (dystrophia myotonica–protein kinase) located on chromosome 19q13.3.
- Genetic Anticipation: The length of the CTG repeat often increases significantly between generations, leading to more severe manifestations in offspring.
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Myotonic Dystrophy Type 2 (DM2)
- Previously known as proximal myotonic myopathy, DM2 is much rarer and typically not observed in childhood.