DESCRIPTION
Congenital myopathies cause a child’s muscles to be smaller and weaker than normal. This may lead to breathing and trouble eating in infancy. It can also lead to delayed motor development.
Forms of Congenital Myopathies
There are many different forms of CMs. They can be classified in one of two ways:
- By the result of a muscle biopsy. They can be classified according to the results of a muscle biopsy. In this case, they will be divided into categories such as:
- Centronuclear myopathies
- Nemaline rod myopathies
- Central core myopathies
- Congenital fiber-type disproportion
- By the result of genetic testing. They can be classified based on the abnormal gene causing the disorder. For instance:
- MTM1
- NEB
- RYR1
- ACTA1
Severity Levels
More Severe
The most severe forms of CMs may make a child unable to:
- Breathe on their own
- Swallow
- Cough effectively
In these cases, the breathing problems may be so severe that a breathing machine is needed to keep the child alive. Without a breathing machine, a severely affected child may die. Further, with weakened breathing, swallowing, and coughing muscles, respiratory infections like pneumonia can be life-threatening. A feeding tube may be needed for some children to get enough calories in their diet if the muscles that help with chewing and swallowing are very weak.
Less Severe
Types of Muscles Affected
Typically, the muscles most affected are the hips and shoulders. The hands and feet are usually less affected, though there are exceptions.
The muscles of the face and head may be affected. This can lead to:
- An elongated facial structure (this may be a called a “myopathic facies”)
- Decreased movement of the muscles that control facial expression
The muscles that hold up the eyelids and that control movement of the eyes side-to-side and up-and-down may also be weak. This can lead to drooping eyelids and double vision.
CAUSES
Congenital myopathies are genetic diseases. This means that they are caused by a change in the affected person’s DNA. This can happen in four different ways:
1. Dominant inheritance
2. Recessive inheritance
3. X-linked inheritance
4. De novo
CMs are not caused by anything that either parent did or did not do during the pregnancy.
In some cases, a genetic cause is suspected, but cannot be found with genetic testing. This occurs about 50% of the time. In these cases, a muscle biopsy may be the best way to confirm the diagnosis. However, new genetic testing strategies may be able to help doctors reach a diagnosis in these unsolved cases in the coming years.
LABORATORY INVESTIGATIONS
While clinical symptoms are a first step in making a diagnosis, lab investigations are also important:
- Genetic testing. A genetic test can quickly reveal the genetic cause of CMs. However, sometimes, a first genetic test does not show changed genes. In these cases, broader genetic tests, such as whole exome sequencing or whole genome sequencing, may be helpful.
- Blood testing. A blood test for creatine kinase, a protein in muscle tissue, may also be performed. The level of this protein is usually normal in CMs. However, it is elevated in muscular dystrophies.
- Electromyogram (EMG) testing. An EMG is an electrical test of the muscles and nerves. An EMG and a nerve conduction study can help doctors tell CMs from similar diseases.
- Muscle imaging. Images of the muscles using magnetic resonance imaging (MRI) and ultrasound can be used for diagnosing CMs. They may show abnormal-appearing muscles. However, these images are rarely specific enough to make a definitive diagnosis.
- Muscle biopsy. In a muscle biopsy, a small sample of a muscle is examined. This sample is taken by a surgeon. This can be very helpful in confirming signs of CMs in the muscle tissue itself. Signs include:
- Central nuclei
- Central cores
- Nemaline rods
- Fiber-type disproportion
Resources
Cure CMD’s mission is to advance research toward treatments for congenital muscular dystrophy (CMD), and improve the lives of those living with CMD through engagement and support of the affected community. Cure CMD offers Peer Match and Mentorship programs, a Pulmonary Care Web Series, Resources for Clinicians & Scientists, CMD Virtual Happy Hours, an extensive video library, and many other resources. You will find community support opportunities, as well as clinical descriptions and care guidelines for each CMD subtype.
Cure CMD also manages the Congenital Muscle Disease International Registry, where affected individuals with congenital muscular dystrophy, congenital myopathy, congenital myasthenic syndrome, and some forms of limb girdle muscular dystrophy, can participate in research and be notified about opportunities to enroll in clinical studies and trials.
Muscular Dystrophy Association
Families are at the heart of Muscular Dystrophy Association’s mission. A caring and concerned group of families started MDA in 1950, and they continue to relentlessly pursue their promise to free families from the life-threatening effects of muscular dystrophy and muscle-debilitating diseases today. MDA focuses on over 43 neuromuscular diseases in children and adults.
MDA empowers families with support by providing: A Resource List, Outside Organization Programs & Information, Summer Camp, Community Education, Community Events, and Young Adult Programs. MDA’s research program awards grants to the world’s best scientists investigating promising theories and therapies that may accelerate treatments and cures for families living with muscular dystrophy, Amyotrophic Lateral Sclerosis (ALS), and related neuromuscular diseases.
Publications
JCN: What Your Pediatric Neurologist Wants You to Know
Podcast from SAGE Neuroscience and Neurology/Journal of Child Neurology (JCN). JCN’s Residents and Fellows Board Director, Dr. Alison Christy, interviews Dr. Farida Abid, Assistant Professor in Pediatric Neurology at Texas Children’s Hospital about Neuromuscular disease.
