Types of Myotonic Dystrophy
There are two well-characterized types of myotonic dystrophy: DM1 or Type 1 and DM2 or Type 2, also known as PROMM. They are caused by mutations in different genes, but have many overlapping symptoms. The relative prevalence of each type is not well established. DM1 is estimated to affect 1 in 8,000 individuals. DM2 was previously considered to be less common; however, as the gene mutation for DM2 was identified just a few years ago, researchers are now discovering that this form might be more prevalent than originally thought.
Both DM1 and DM2 are characterized by skeletal and smooth muscle weakness and myotonia, heart abnormalities, cataracts and insulin resistance. DM1 can occur from birth to old age, and is divided into further subtypes based on the age of the affected individual when symptoms first appear. Symptoms vary greatly between patients, from minor muscle pain to serious respiratory and cardiac issues. The congenital form of DM1 is the most severe version and has distinct symptoms that can be life-threatening. In contrast, DM2 has only an adult onset form and symptoms tend to impact daily living in later life. As well, fewer systems are affected in individuals with DM2 and their symptoms tend to be less severe.
Researchers suspect additional types of the disease may exist. A novel form of DM (called DM3) has been identified in a very small group of patients who exhibit myotonic dystrophy symptoms but carry neither the DM1 nor the DM2 mutation. It is not clear whether this is a truly distinct category of myotonic dystrophy or whether some unknown factors may be confounding diagnosis in these patients.
The table below outlines the different types of myotonic dystrophy. Further information on each type can be obtained by clicking the links contained in the table.
Types | Mutation Site | Subtypes | Category |
DM1 | DMPK (Dystrophia myotonica protein kinase) gene on chromosome 19 |
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| Mild or Classical | |
Znf9 (Zinc finger 9) gene on chromosome 3 |
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