What is Myotonic Dystrophy?

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.

Signs, Symptoms and Progression

The severity and progression of the disease vary among individuals, but in general, symptoms progress gradually. Typical symptoms include:

  • Progressive muscle wasting and weakness
  • The inability to relax muscles at will (myotonia)
  • Abnormal heart rhythm and heart muscle weakness
  • Development of cataracts relatively early in life
There are two major types of myotonic dystrophy, type 1 (DM1) and type 2 (DM2), caused by mutations in different genes. The signs and symptoms overlap between the two types, although DM2 tends to be milder. In addition, DM1 primarily affects distal muscles, away from the center of the body, such as those of the lower legs, hands, and face. DM2 primarily involves proximal muscles, close to the center of the body, such as those of the shoulders, elbow, and hips. DM1 can be congenital or begin during childhood, often characterized by cognitive and behavioral abnormalities. The most common type of DM1 is the adult-onset form, and DM2 rarely begins in childhood.

Causes and Inheritance

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.

Management and Treatment

There is no cure for DM, but medications and therapy can help manage some of its symptoms.