Myotonic Dystrophy

What is myotonic dystrophy?

Myotonic dystrophy (DM) is a complex, inherited condition that mainly causes progressive muscle atrophy and weakness. People with the condition often have prolonged muscle contractions (myotonia) and can’t relax certain muscles after using them.

Myotonic dystrophy (DM) has a wide range of symptoms. It can affect several body systems, including your:

• Skeletal muscles and heart muscles.
• Eyes.
• Cardiovascular system.
• Endocrine system.
• Central nervous system.

There are two main forms of myotonic dystrophy:

• Myotonic dystrophy type 1 (DM1), also known as Steinert disease. DM1 has four types: classic, mild, congenital and childhood.
• Myotonic dystrophy type 2 (DM2), also known as proximal myotonic myopathy.

Their symptoms overlap, but DM2 tends to be milder than DM1.

What is the difference between muscular dystrophy and myotonic dystrophy?

Muscular dystrophy refers to a group of more than 30 inherited (genetic) conditions that cause muscle weakness. These conditions are a type of myopathy, a disease of your skeletal muscles. Over time, your muscles shrink and become weaker. This affects your ability to walk and perform daily activities. It can also affect your heart and lungs.

Myotonic dystrophy is one type of muscular dystrophy. It’s the most common form of muscular dystrophy that begins in adulthood. (But certain types of myotonic dystrophy begin in infancy or childhood.)

Who does myotonic dystrophy affect?

Different forms of myotonic dystrophy begin at different ages:

• Classic myotonic dystrophy type 1: This form usually begins in your 20s, 30s or 40s.
• Mild myotonic dystrophy type 1: This form affects people 20 to 70 years old (typically after the age of 40).
• Congenital myotonic dystrophy type 1: This form affects infants (“congenital” means “present at birth”).
• Childhood myotonic dystrophy type 1: This form usually begins around the age of 10.
• Myotonic dystrophy type 2: This form typically begins in adulthood. The average age of onset is 48 years.

How common is myotonic dystrophy?

Myotonic dystrophy (DM) affects at least 1 in 8,000 people across the world, though the prevalence of it varies among different geographic and ethnic populations. DM is the most common muscular dystrophy in people of European ancestry.

In most populations, type 1 is more common than type 2.

What are the symptoms of myotonic dystrophy?

The main symptoms of myotonic dystrophy include the following, which get progressively worse over time:

• Muscle atrophy (wasting).
• Muscle weakness.
• Myotonia.

Myotonia is the inability to relax muscles at will. For example, it may be difficult for someone with DM to let go of a door handle after grasping it.

However, DM can affect many different parts of your body and cause a variety of other symptoms. The severity and rate at which these symptoms develop depend on the type of DM.

Symptoms of classic myotonic dystrophy type 1

Symptoms of classic myotonic dystrophy type 1 begin in adulthood. Myotonia is the main initial symptom. It’s often more obvious after rest and improves with muscle activity.

Other symptoms include:

• Distal muscle weakness (the muscles farthest from the center of your body), which results in difficulty with fine motor tasks involving your hands and an impaired gait due to foot drop.
• A thin, sharp face (myopathic face) due to wasting of facial muscles.
• Heart conduction abnormalities.

Symptoms of congenital myotonic dystrophy type 1

Signs of congenital myotonic dystrophy before birth include:

• Decrease in fetal movement in the uterus.
• Polyhydramnios (too much amniotic fluid around the fetus during pregnancy).
• Clubfoot.
• Ventriculomegaly (enlarged brain ventricles due to a buildup of cerebrospinal fluid).

Symptoms of congenital DM in children and adults include:

• A tented appearance of your upper lip that results from weak facial muscles.
• Slurred speech (dysarthria).
• Intellectual disability.
• Decreased muscle tone (hypotonia), rather than myotonia.

Symptoms of mild myotonic dystrophy type 1

Symptoms of mild myotonic dystrophy type 1 typically begin between the ages of 20 and 70 years. They include:

• Mild muscle weakness.
• Myotonia.
• Cataracts.

Symptoms of childhood myotonic dystrophy type 1

Symptoms of childhood myotonic dystrophy type 1 usually begin around age 10. They include:

• Learning difficulties and psychosocial problems, such as family problems, depression and anxiety.
• Slurred speech.
• Hand muscle myotonia.
• Heart conduction abnormalities.

Symptoms of myotonic dystrophy type 2

Symptoms of myotonic dystrophy type 2 (DM2) typically begin in adulthood and can vary.

Symptoms can include:

• Proximal muscle (the muscles closer to the center of your body) weakness or stiffness.
• Myofascial pain.
• Early-onset cataracts (occurring before the age of 50).
• Varying grip myotonia.
• Hearing loss.

Pain is one of the primary complaints in DM2. People with DM2 describe it as abdominal, musculoskeletal and exercise-related pain.

What causes myotonic dystrophy?

Myotonic dystrophy (DM) is inherited (passed from parent to biological child).

Mutations (changes) in the DMPK gene cause myotonic dystrophy type 1, while mutations in the CNBP gene cause type 2.

Similar changes in the structure of the DMPK and CNBP genes cause myotonic dystrophy type 1 and type 2. In each case, a segment of DNA is abnormally repeated many times, forming an unstable region in the gene. The more times the DNA is abnormally repeated, the more severe the symptoms of DM are.

Scientific evidence suggests that excess messenger RNA generated from the abnormal DNA repeats is toxic and interferes with the production of many proteins in cells, which, in turn, causes signs and symptoms in various organs in myotonic dystrophy.

Myotonic dystrophy inheritance

Both types of myotonic dystrophy are inherited in an autosomal dominant pattern. When a trait is autosomal dominant, only one parent needs to have an altered gene to pass it on. Half of the children of a biological parent with an autosomal trait will get that trait.

As myotonic dystrophy type 1 is passed from one generation to the next, the condition generally begins earlier and earlier in life, and signs and symptoms become more severe. This phenomenon is called anticipation.

How is myotonic dystrophy diagnosed?

If you’re experiencing symptoms of myotonic dystrophy (DM), a healthcare provider will perform a physical exam and ask questions about your:

• Personal medical history.
• Family medical history, especially a history of DM.
• Symptoms.

Certain medical tests can help confirm a myotonic dystrophy diagnosis.

What tests will be done to diagnose myotonic dystrophy?

Genetic testing can confirm a diagnosis of myotonic dystrophy (DM). The testing looks for mutations in the DMPK gene (in DM1) or the CNBP gene (in DM2).

If your healthcare provider is unsure if you may have DM or another condition, they may order one or more of the following tests before recommending genetic testing:

• Creatine kinase blood test: Creatine kinase is an enzyme that mainly exists in your heart and skeletal muscle. The cells in your skeletal muscles or heart muscles release creatine kinase into your blood when they’re damaged. In people with mild myotonic dystrophy, it may be mildly elevated but is typically normal.
• Electromyogram (EMG): This test involves checking electrical activity of muscle fibers using a fine needle electrode that’s inserted into your muscles. Typically, people with myotonic dystrophy have excessive waxing and waning electrical activity in their muscles at rest.
• Muscle biopsy: For a muscle biopsy, a provider will remove a small sample of tissue and cells from one of your muscles. They’ll then analyze it under a microscope to look for signs of DM.

If these tests confirm a diagnosis of DM, your provider will likely recommend more tests to check the functioning of certain organs DM can affect. These tests include:

• Electrocardiogram to check your heart function.
• Pulmonary (lung) function testing to check for neuromuscular respiratory failure.
• Sleep study to check for obstructive sleep apnea and hypersomnia (daytime sleepiness).

How is myotonic dystrophy treated?

There’s no cure for myotonic dystrophy (DM). Treatment instead focuses on:

• Managing symptoms.
• Maximizing quality of life and independence.

DM can affect many different parts of your body. Depending on your symptoms, treatment may include:

• Medications that reduce sustained myotonia, including sodium channel blockers such as mexiletine, tricyclic antidepressants, benzodiazepines or calcium antagonists.
• A CPAP machine for sleep apnea.
• Neurostimulants such as methylphenidate for excessive daytime sleepiness.
• Cataract surgery for cataracts that impair your vision.
• Treatment for diabetes, which may involve medications in pill form and/or insulin. People with DM are at an increased risk of diabetes from insulin resistance.
• Synthetic testosterone for the treatment of low testosterone (male hypogonadism). Men and people assigned male at birth with DM1 commonly have low testosterone and erectile dysfunction.

Physical and occupational therapy are a significant part of maximizing independence for people with DM. It can help strengthen your muscles and help you learn new ways of performing daily tasks. Assistive devices, such as braces, canes or a wheelchair can also help with independence.

Speech-language pathology (SLP) can help with difficulty swallowing (dysphagia) and slurred speech (dysarthria).

Can myotonic dystrophy be prevented?

As myotonic dystrophy (DM) is an inherited condition, there’s nothing you can do to prevent it.

If you’re concerned about the risk of passing on DM or other genetic conditions before trying to have a biological child, talk to your healthcare provider about genetic counseling.

What is the prognosis of myotonic dystrophy?

The prognosis (outlook) of myotonic dystrophy (DM) depends on the type and the age it begins. An earlier age of symptom onset is generally associated with poorer outcomes and reduced survival rates.

Up to 50% of people with myotonic dystrophy type 1 need a wheelchair for mobility before death. People with myotonic dystrophy type 2 have milder symptoms and typically don’t need assistive devices for mobility.

What is the life expectancy of someone with myotonic dystrophy?

The average life expectancy for myotonic dystrophy depends on the type.

The neonatal mortality rate (death that occurs within 28 days after birth) is around 18% for infants with congenital DM1. About 25% of people with congenital DM1 die before 18 months of age and 50% die before their mid-30s.

People with mild DM1 usually have normal lifespans. Lifespan is reduced compared to average in classic DM1.

Is myotonic dystrophy fatal?

Myotonic dystrophy (DM) can be fatal, though the age at which DM may cause death depends on the type. The leading cause of death in DM is neuromuscular-associated respiratory failure, followed by cardiovascular complications.

When should I see my healthcare provider about myotonic dystrophy?

If you’re experiencing symptoms of DM, such as muscle weakness or myotonia, talk to a healthcare provider.

If you have DM, you’ll need to see your healthcare team regularly to make sure your current treatment plan is working for you.

A note from Cleveland Clinic

It can be overwhelming to learn you or your child have a new diagnosis. It’s important to remember that no two people with myotonic dystrophy (DM) are affected in the same way. The best way you can prepare is to talk to healthcare providers who specialize in researching and treating DM. They’ll offer treatment options and answer any questions you have.