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Congenital Myotonic Muscular Dystrophy


What Is Congenital Myotonic Muscular Dystrophy?

Congenital myotonic muscular dystrophy (congenital MMD) is a rare type of muscular dystrophy. Muscular dystrophy is a genetic disease that affects the muscles and weakens them over time.

Kids who have congenital MMD were born with it (congenital means "present at birth"). Myotonic means that the muscles don't relax normally after they contract (squeeze together). The muscles are stiffer than they should be.

Myotonic muscular dystrophy is also called DM because its name in Latin is dystrophia myotonica.

What Are the Signs & Symptoms of Congenital MMD?

Babies born with congenital myotonic (mye-uh-TAHN-ik) muscular dystrophy:

  • don't move much before or after birth
  • have little muscle strength and are often described as "floppy"
  • have a weak cry
  • have trouble breathing and feeding
  • may have weakness in their facial muscles
  • often have one or both feet turned in (clubfoot)

Congenital MMD often causes other problems, including:

  • trouble with learning
  • speech and hearing problems
  • strabismus (one eye does not move with the other)
  • delay in reaching milestones such as sitting up alone, crawling, and walking

Usually, most of the muscle problems go away in early childhood, but return when the child is a teenager or young adult.

What Causes Congenital Myotonic Muscular Dystrophy?

The two types of myotonic muscular dystrophy in adults are MMD1 and MMD2. Only MMD1 (also called DM1) causes congenital MMD.

MMD1 can develop:

  • at birth (congenital MMD)
  • in childhood
  • most commonly, during adulthood (adult-onset MMD)

MMD1, including congenital MMD, happens because of a mutation (a change) in a child's genes (DNA). The mother of a child with congenital MMD almost always has MMD too, but might not know it because she hasn't had muscle problems.

In congenital MMD, a stretch of DNA (called the DMPK gene) has a mutation that makes it longer. The longer gene creates clogs in normal muscle cell activity. The clogged-up cells slowly die.

After the DMPK gene changes, it tends to get even longer with every generation. As the condition passes from one generation to the next, symptoms usually start earlier in life and become more severe.

How Is Congenital Myotonic Muscular Dystrophy Diagnosed?

A doctor may suspect congenital MMD before a child is born if the mother is known to have MMD or if an ultrasound scan before birth shows something unusual. Ultrasound findings that may suggest MMD include:

  • less fetal movement than expected
  • a lot more fluid in the uterus (womb) than usual

After birth, doctors may suspect congenital MMD if the baby:

  • has low muscle tone (the tension in muscles needed for normal movement)
  • doesn't move much
  • has trouble swallowing
  • needs help to breathe

Tests that will help make sure the problem is congenital MMD include:

  • Creatine kinase (CK) level: This blood test may show that there's a problem with the muscles.
  • Genetic testing: This test looks to see if the DMPK gene is longer than normal. Knowing this helps doctors predict what the child and family can expect. Family members can be tested to see if they have the mutation.

If the genetic testing is negative or does not find a problem in the DMPK gene, doctors might do these tests:

  • Electromyography (EMG): This study tests nerve and muscle action to make sure the problem is in the muscle and not in the nerve that controls it.
  • Muscle biopsy: Doctors take a small piece of muscle, usually from the thigh, to check for any changes that suggest a muscle disease.

With genetic testing being more common, an EMG and muscle biopsy are done much less often.

How Is Congenital Myotonic Muscular Dystrophy Treated?

There is no cure yet for congenital MMD. At first, babies receive intensive care, including breathing and feeding support. Over time, they typically gain strength slowly and usually begin breathing and swallowing more easily.

Sometimes medicines can reduce the tightness in the muscles of the hands and body.

Many parts of the body are involved in myotonic muscular dystrophy. Finding a clinic with specialists who treat problems affecting the lungs, digestive tract, eyes, heart, bones, and muscles can help kids get the best possible care.

As they get older, kids and teens will need care from different medical specialists, including:

Assistive devices needed might include:

  • bracing to improve flexibility
  • power wheelchairs and scooters to improve mobility
  • a ventilator to support breathing
  • robotics to help with routine daily tasks

What Else Should I Know?

Doctors will check a child with congenital MMD regularly to look for:

  • eye problems
  • heart problems
  • digestive problems
  • diabetes

Children with muscular dystrophy may have a harmful response to anesthesia. If your child must have surgery, make sure the doctor and anesthesiologist are aware of the condition, even if the surgery is not related to MMD. People with MMD have weaker breathing muscles and need closer monitoring during and after surgery.

Looking Ahead

Research has helped doctors understand a lot about how the DMPK gene causes muscle problems in people with congenital MMD. Scientists are testing new possibilities for treatment.

For more information about muscular dystrophy, visit:

Reviewed by: Mena T. Scavina, DO
Date reviewed: July 2019