Congenital myopathy

What is congenital myopathy?

A child with congenital myopathy typically has low muscle tone and reduced strength because their muscles do not work normally. The symptoms are often noticeable when a baby is born.

• Physical (gross motor) skills – like rolling over – usually develop late.

• Fine motor skills – such as holding a pencil – may also be affected.

Language and thinking develop as they would in other children, but a child with congenital myopathy may have difficulty speaking. After about a year, a child’s loss of strength usually levels off or progresses very slowly.

What are the different types of congenital myopathy?

There are many types of congenital myopathy that cause different kinds of muscle weakness. Some are identified by the muscles they affect or by a muscle biopsy, and some can be identified by a change in a specific gene.

The main types of congenital myopathy include:

• Nemaline myopathy - This is more common than some other types. Babies with this form of congenital myopathy typically have weakness in the neck, face, arms and legs. They might also have trouble feeding and breathing starting right after birth.

• Central core disease - Children with central core disease can have muscle weakness and developmental problems. This type is caused by a defect in a gene called RYR1, which can also make a child susceptible to severe reactions to certain drugs used in anesthesia.

• Multiminicore disease - This congenital myopathy can cause scoliosis and severe muscle weakness in the arms and legs. It can be due to a defect in the RYR1 gene or other genes. If it is caused by RYR1, your child may react severely to certain drugs used in anesthesia.

• Centronuclear myopathy and myotubular myopathy - Centronuclear myopathy is a group of congenital myopathies that cause weak muscles in the face, arms and legs. The most common type, myotubular myopathy, mainly affects boys. Children with this condition may have difficulty feeding and breathing right after they are born. Myotubular myopathy is caused by a defect in the MTM1 gene.

• Congenital fiber type disproportion myopathy - This type causes weakness in the face, neck, trunk, arms and legs. Doctors will confirm this diagnosis with a muscle biopsy.

What are the signs and symptoms of congenital myopathy?

Different types of congenital myopathy can affect different parts of the body.

In general, signs and symptoms include:

• Lack of muscle tone

• Weak muscles

• Difficulty speaking and breathing

• Weak muscles in the face

• Drooping eyelids

• Delayed motor skills (sitting, raising their head, rolling over)

• Muscle cramps or tightening of muscles (contractures)

How is congenital myopathy diagnosed?

A doctor will check your child for signs and symptoms of congenital myopathy, particularly low muscle tone and muscle weakness. To rule out muscular dystrophy (which can look similar to congenital myopathy in babies), they will test for an enzyme called creatine kinase (CK). Children with muscular dystrophy have high levels of this enzyme, but those with congenital myopathy have normal or slightly high levels.

After ruling out muscular dystrophy, a doctor will do a genetic test of a blood sample to try to identify a specific type of congenital myopathy. If the results of the genetic tests are not certain, a neurologist may do other tests.

For example, they may take a small sample of muscle (biopsy) and look at it under a microscope. They may also do nerve conduction and electromyography (EMG) tests to learn whether the problem starts with the muscles or the nerves.

What causes congenital myopathy?

Congenital myopathies are caused by genetic changes (mutations). Sometimes these conditions are inherited from a parent, but they also can be caused by random mutations in a gene or genes.

Doctors do not know what causes these random changes.

How is congenital myopathy treated?

There is no cure for congenital myopathy, but the team of experts at Children’s Health will work together to treat your child. Because the muscle weakness usually levels off after a year or so, the goal is to improve key functions and keep your child as independent as possible.

Different specialists can help treat different parts of the body, including:

• Pulmonologists - Children whose breathing and lungs are affected

• Cardiologists - Children whose condition affects their heart

• Gastroenterologist - Helps children with problems that affect their digestive system

• Orthopedic surgeons - For children whose condition affects their bones, joints and soft tissues

• Neuromuscular nurses - To care for a child’s nerves and muscles

At Children’s Health, your child may also receive treatments that include:

• Physical Therapy (PT)

• Occupational therapy (OT)

• Respiratory therapy

• Speech therapy

• Nutrition therapy