What is Congenital Muscular Dystrophy?
Congenital muscular dystrophy is a type of muscle weakness disorder that can show up in babies soon after they’re born or during their infancy. This disorder differs from congenital myopathies, another type of muscle weakness in children, in its progression. Muscular dystrophies tend to get worse over time and are often linked to increased muscle breakdown as a child gets older.
On the other hand, congenital myopathies are usually caused by genetic, metabolic, or other factors, and remain generally constant in their progression. This means that they don’t typically get worse over time. These disorders are categorized based on results from muscle biopsies and genetic evaluations.
In a muscle biopsy, scientists look at a small piece of muscle tissue under a microscope to see if there are any abnormalities. With these disorders, things like muscle fiber shrinkage and fibrofatty infiltration, which is the presence of excess fat and fibrous tissue, are usually observed.
What Causes Congenital Muscular Dystrophy?
Many of these diseases are inherited and tied to specific genes. The conditions affect how proteins are created in the plasma membrane – a thin layer surrounding cells – and the extracellular matrix which is basically the space between cells. Most of these are inherited in an autosomal recessive way which means a person needs to inherit the faulty gene from both parents to get the disease.
Duchenne, a kind of muscular dystrophy, is an exception because it’s tied to the X chromosome, and therefore, typically only affects boys. Most girls who have the gene are just carriers, but some might also experience mild to medium muscle weakness. Both Duchenne and another condition called Becker dystrophy come from a mutation in the same gene – the dystrophin gene. However, in Duchenne, this gene makes a faulty and shortened protein, while in Becker it makes a partly functional protein.
Some other inherited muscle diseases are Walker Warburg, muscle-eye-brain disease, and Fukuyama disease, which all come from a mutation in a shared protein called a-dystroglycan. Another disease, myotonic dystrophy, usually comes from a faulty gene that’s passed down in an autosomal dominant way, where only one parent needs to pass down the faulty gene for the child to get the disease.
Finally, two other muscle conditions, Ulrich and Bethlehem myopathy, result from changes to the collagen VI molecules – a type of protein – in three known genes. These conditions might be autosomal recessive, needing both parents to pass down the faulty gene, or autosomal dominant, needing only one parent to do so.
Risk Factors and Frequency for Congenital Muscular Dystrophy
Duchenne muscular dystrophy is the most frequently observed type amongst all congenital muscular dystrophies. It generally affects about 1 in 3600 boys. Studies have shown that the occurrence rate of congenital muscular dystrophies in children globally is around 0.82 per 100,000 children. It’s noteworthy that some specific types of muscular dystrophy are more common in certain geographical areas. For instance, Fukuyama muscular dystrophy is most frequently found in Japan.
Signs and Symptoms of Congenital Muscular Dystrophy
People with muscular dystrophies can potentially exhibit signs of the condition during pregnancy. These signs may include abnormal amounts of amniotic fluid that could be the result of the baby swallowing less amniotic fluid and having smaller movements in the womb. At birth, these infants may have a weak cry and display minimal movements. They can also have low muscle tone and, in severe cases, joint contractures.
When talking to the parents, it may come to light that the infant has trouble feeding due to a weak sucking ability. As the child grows, notable motor delays can be a symptom. The extent of muscle weakness varies depending on the type of muscular dystrophy and how much the abnormal protein is affected. If an infant is suspected of having low muscle tone, a thorough physical examination should be done. This helps to exclude possible anomalies in other organs and assess potential syndromic associations.
The time the symptoms begin (infancy or childhood) and the muscles affected can limit the potential diagnoses to a smaller group of disorders.
Testing for Congenital Muscular Dystrophy
If your baby shows signs of low muscle tone (hypotonia), doctors will carry out several tests to find out the reason. This includes:
Firstly, a neurologist (a doctor who specializes in the nervous system) will check your infant’s joint power and reflexes through a complete check-up.
Secondly, they will consider carrying out blood tests like creatine kinase level (CK), aldolase, alanine aminotransferase (ALT), and aspartate aminotransferase (AST). Additionally, nerve conduction studies and EMG (tests that check the health of muscles and the nerves controlling them) may be performed. Do note that CK levels could range from normal to significantly high depending on the type of hypotonia condition.
In the past, muscle biopsy used to be routinely done for these disorders, but with the advent of genomic sequencing – the process that determines the complete DNA sequence of an organism’s genome – it is no longer necessary in all cases. However, special tests like immunohistochemistry and electron microscopy may be carried out to help identify specific diseases.
Moreover, echocardiography and EKG tests (which examine the heart’s structure and function) need to be performed because issues like cardiomyopathy and irregular electrical activity can happen with these disorders. Brain imaging with MRI is also necessary as it can reveal any potential abnormalities in different areas of the brain, which are commonly found in these disorders.
Some specific diseases like Fukuyama dystrophy and muscle eye brain disease are linked to eye problems like short-sightedness, strabismus, cataract, and glaucoma. Therefore, tests to rule out these illnesses might be necessary.
Finally, the last step is confirming the disorder. This is achieved by testing for a specific protein or genetic change, which should ideally be done in a lab that specializes in genetic testing.
Treatment Options for Congenital Muscular Dystrophy
For most of these conditions, the main approach is to manage symptoms, as replacing specific proteins and genes has mostly been tried on animals. Testing these treatments in humans is still mostly experimental, being part of clinical trials.
Many medical centers that handle these patients often have teams made up of various specialists. These teams assist caregivers in caring for these patients who have multiple complex needs at home.
If the patients’ respiratory muscles are affected, they may require machine-assisted breathing at home, with the help of parents and home nurses.
Intensive physical and occupational therapy is an important part of the care plan for these patients during their hospital stay, and it should continue at home.
These patients may need surgery for other health issues like scoliosis caused by long periods of immobility, or to insert a feeding tube to meet their nutritional needs. Due to their usual underweight status and the risk of nutrient deficiencies that can worsen their muscle weakness, maintaining proper nutrition is key in the long-term management of these patients.
Many of these patients may have normal intellectual abilities and could benefit from the assistance of psychologists or psychiatrists to help them handle the stress of living with a chronic disease.
What else can Congenital Muscular Dystrophy be?
If a baby shows signs of weakness early in life, doctors will consider several possible causes:
- Born with muscle disorders (congenital myopathies) such as central core disease, nemaline myopathy, and centronuclear myopathy. Sometimes, these conditions can result from problems with how the body processes energy from food, like carbohydrates and fats.
- Problems with the points where nerves and muscles meet (myoneural junction disorders). These are quite rare but it’s important to rule them out when a baby shows weakness. They include a condition where a baby is born with a muscle weakness disorder called congenital myasthenia gravis and a rare illness caused by bacteria called infant botulism.
- Nerve disorders (neuropathies), which mainly affect nerve roots in the spinal cord and nerves in the body. Common ones that show symptoms in early childhood include Spinal Muscular Atrophy (SMA) and Hereditary Motor Sensory Neuropathy (HMSN).
Remember, it’s critical for healthcare professionals to consider all of these possibilities when a baby shows signs of weakness so they can properly diagnose and treat the child.
What to expect with Congenital Muscular Dystrophy
Most of the time, the treatment for these disorders is focused on managing symptoms, which means long-term outcomes can be unfavorable and life expectancy varies. This is often influenced by the relationship between the genetic issue causing the disorder and the resulting physical changes caused by the abnormal protein.
The primary reason for health complications and death in these disorders typically stems from heart or lung complications, brought on by muscle weakness.
Possible Complications When Diagnosed with Congenital Muscular Dystrophy
There are various health risks related to different body systems that can occur due to chronic conditions or muscle weakness. Here are few of them:
Respiratory System:
- Chronic respiratory failure, due to muscle weakness, could cause lung collapse (atelectasis), choking on food or drink that goes into your lungs (aspiration), and lung infection (pneumonia) as an impact of machine-aided breathing.
Cardiac System:
- Patients might develop an issue with the heart muscle, known as cardiomyopathy. They could also have chronic heart failure which might require medication.
Musculoskeletal System:
- Due to the inability to move, these patients can develop a curved spine (scoliosis), weakened bones (osteopenia), and a higher risk of fractures. Despite aggressive physical therapy, they might develop bed sores and stiff, immobile joints (joint contractures).
Endocrine System:
- These patients often have adrenal insufficiency and might need steroids during stressful periods. It’s important to regularly check thyroid and vitamin D levels as part of their overall health evaluation.
Neurological System:
- Some of these patients might experience seizures, and there is a high prevalence of psychological disorders such as depression and anxiety due to the constant presence of chronic disease.