Myotonic Dystrophy is a form of genetic muscular dystrophy characterized by skeletal muscle weakness and myotonia (difficulty relaxing muscles after use), cardiac abnormalities, cataracts, and other abnormalities. Myotonic Dystrophy is often is abbreviated as “DM” in reference to its Greek name, dystrophia myotonica.
The severity and progression of the disease vary among individuals, but in general, symptoms progress gradually. Typical symptoms include:
Type 1 DM (DM1) is caused by an abnormal trinucleotide repeat expansion in the gene DMPK on chromosome 19. Type 2 (DM2), the milder version, is caused by an abnormal trinucleotide repeat expansion in the gene ZNF9 (also known as CNBP) on chromosome 3. Both types are inherited in an autosomal dominant pattern.
A diagnosis of myotonic dystrophy may be suspected based upon a thorough clinical evaluation, a detailed patient and family history, and identification of characteristic physical findings. Other tests that may be used include electromyography (EMG), blood tests for creatine kinase, and magnetic resonance imaging (MRI) of the brain. Genetic testing, usually using a blood sample, can confirm a diagnosis of DM1 or DM2.
There is no cure for DM, but medications and therapy can help manage some of its symptoms.