An inherited disorder that primarily causes progressive muscle loss, weakness, and myotonia is called myotonic dystrophy (DM). It may also negatively affect the heart, lungs, eyes, and other parts of the body. Unfortunately, it is not possible to cure this condition. That’s why the treatment focuses on relieving the symptoms, preventing life-threatening complications, and improving your quality of life.
While DM usually causes muscle weakness, people with this condition may experience a wide range of symptoms because it affects multiple body systems. These include the skeletal muscles, the cardiovascular system, the endocrine system, and the central nervous system. Physicians have also divided this condition into 2 categories. For example:
- Myotonic dystrophy type 1 (DM1) – This type is also known as Steinert disease, and it has four subtypes, including classic, mild, congenital, and childhood.
- Myotonic dystrophy type 2 (DM2) – This form of DM is also known as proximal myotonic myopathy, and it tends to cause milder symptoms compared to the first type.
In general, DM negatively affects at least 1 in 8,000 people in the world. It happens more commonly in people of European ancestry. Most of them develop the first type of DM. Usually, the symptoms appear differently among people with this condition because they depend on which type a person develops. Check some examples below:
- Classic myotonic dystrophy type 1 – It often appears between 20 and 40 years old.
- Mild myotonic dystrophy type 1 – This type can occur in people between the ages of 20 and 70 (more commonly after 40 years old).
- Congenital myotonic dystrophy type 1 – This form of DM mostly affects children. The term congenital means present at birth.
- Childhood myotonic dystrophy type 1 – It starts around the age of 10.
- Myotonic dystrophy type 2 – While the average onset is 48 years, it may happen in early adulthood.
What is The Difference between Muscular Dystrophy and Myotonic Dystrophy?
The medical term used to describe multiple health conditions that cause muscle weakness is muscular dystrophy. It also refers to a group of multiple inherited disorders. Moreover, all types of muscular dystrophy are a type of myopathy (a disorder that negatively affects skeletal muscles). However, myotonic dystrophy is a type of muscular dystrophy (the most common form that often causes symptoms during adulthood).
Symptoms
While the primary symptoms of DM are muscle atrophy (loss), muscle weakness, and myotonia, it may also cause other symptoms, depending on which type a person develops. Examples include:
Classic Myotonic Dystrophy Type 1 Symptoms
Usually, the symptoms in people with this type start during adulthood, and one of the most common symptoms is myotonia (inability to relax muscles after their contraction). Check for other symptoms of the classic DM1 below:
- Myopathic face (a thin and sharp face)
- Heart conduction irregularities
- Distal muscle weakness (when it occurs, people may have problems with fine motor skills that involve their hands and an impaired gait)
Congenital Myotonic Dystrophy Type 1 Symptoms
This type can cause symptoms before and after birth. Check some prenatal symptoms below:
- Clubfoot
- Ventriculomegaly (it happens when the brain ventricles become enlarged due to a buildup of cerebrospinal fluid)
- Polyhydramnios (excessive fluid around the fetus during pregnancy)
- Decreased fetal movement in the uterus
However, babies may experience the following symptoms after birth. For example:
- Dysarthria (slurred speech)
- Intellectual disability
- Hypotonia (reduced muscle tone)
- Weak facial muscles
Mild Myotonic Dystrophy Type 1 Symptoms
Those who develop this type of DM often experience mild muscle weakness, myotonia, and cataracts.
Childhood Myotonic Dystrophy Type 1 Symptoms
Examples include:
- Speaking problems due to muscle weakness
- Learning difficulties and psychosocial problems (including family problems, depression, anxiety, and others)
- Heart muscle myotonia
Myotonic Dystrophy Type 2 Symptoms
While one of the most common symptoms of DM2 is pain that occurs in the abdomen and muscles throughout the body, it may also cause other symptoms. Examples include:
- Varying grip myotonia
- Hearing loss (deafness)
- Proximal muscle weakness or stiffness
- Cataracts that often occur before the age of 50
- Myofascial pain
Immediately contact your healthcare professional if any of the symptoms listed above occur. Otherwise, it may lead to serious complications.
Causes
This is an inherited condition, which means certain abnormal (mutated) genes are passed from the biological parents to their biological children during pregnancy. While people with DM1 often have a mutation in their DMPK gene, those who develop the second type have a change (mutation) in the CNBP gene.
Usually, people with these genes have repeated a segment of the DNA multiple times. The more times the DNA is abnormally repeated, the more severe the symptoms caused by the condition are. According to some studies, excessive messenger RNA produced from these abnormal genes is toxic and may negatively affect the production of proteins in cells. That’s why DM affects multiple body systems.
Inheritance
All types of DM are inherited in an autosomal dominant pattern, which means the condition appears even if only one parent has the abnormal gene. Approximately 50% of children with biological parents with an autosomal trait will get it. Nowadays, the DM1 passes from one generation to the next, and symptoms tend to be more severe. This process is called anticipation.
In addition, there is no way to prevent DM because it happens due to an abnormal gene that is passed during pregnancy. The only thing you can do is a genetic test to check for the abnormal genes that cause DM. It is very important to understand the risks of having children with DM.
Diagnosis
Doctors often start the diagnosis of DM with a physical examination and questions about the medical history and symptoms. However, to confirm or exclude DM, doctors often perform the following tests and procedures. Examples include:
- Genetic test – This is the only way to confirm or rule out DM. It is used to check for the abnormal genes that cause this condition, including mutations in the DMPK gene and CNBP gene.
- Creatine kinase blood test – Normally, creatine is an enzyme present in the heart and skeletal muscles. It is usually released by the muscles when they are damaged. High levels of creatine kinase in the blood often indicate muscle damage.
- Electromyography (EMG) – This test helps doctors measure the electrical activity of the muscle fibers.
- Muscle biopsy – During this procedure, physicians will remove a small sample of tissue for testing.
Once you are diagnosed with DM, doctors may perform additional tests to check the function of other organs that this disorder may affect. They often perform pulmonary function testing, sleep study (to check for obstructive sleep apnea and hypersomnia), electrocardiogram (ECG or EKG).
Treatment
The treatment goal is to manage symptoms, prevent serious complications, and improve your quality of life. Physicians often recommend the following options to treat DM and its complications. Examples include:
- Medicines – These include sodium channel blockers (such as Mexiletine), tricyclic antidepressants, benzodiazepines, or calcium antagonists.
- Neurostimulants (such as Methylphenidate) to reduce daytime sleepiness
- Cataract surgery
- CPAP machine
- Insulin for people with diabetes
- Synthetic testosterone to treat male hypogonadism or erectile dysfunction (ED)
Another important aspect of DM treatment is physical and occupational therapy that helps improve the strength of the muscles. In some cases, people may also need assistive devices, including canes, braces, or a wheelchair.
Frequently Asked Questions
What is the life expectancy of people with myotonic dystrophy?
In general, the life expectancy varies among people with DM because it depends on several factors. These include the type and severity of the condition, overall health, age, sex, and their response to treatment. Generally, the mortality (death) rate is about 18% for infants (congenital DM1), and approximately 25% of children with this type die before 18 months of age. While people with mild DM1 often have a normal lifespan, people with classic DM1 have a slightly reduced life expectancy.
Is myotonic dystrophy fatal?
Yes, this condition can be fatal, especially if it is left untreated. The most common causes of death in people with DM are neuromuscular-associated respiratory failure and cardiovascular complications.
When should I see my healthcare provider?
If you or your child experiences any symptoms that resemble DM, immediately see a doctor for a diagnosis and proper treatment. Early detection may help prevent life-threatening complications.
Can myotonic dystrophy skip a generation?
In most cases, myotonic dystrophy does not truly skip a generation because it is inherited in an autosomal dominant pattern. However, some people may have very mild symptoms that go unnoticed, making it appear as though the condition skipped a generation.
Can women with myotonic dystrophy have healthy pregnancies?
Many women with myotonic dystrophy can have successful pregnancies, but they are considered high-risk pregnancies. Close monitoring is important because complications such as excessive amniotic fluid, preterm labor, and an increased risk of having a child with congenital myotonic dystrophy may occur.
Does myotonic dystrophy affect intelligence?
The effect on intelligence varies depending on the type of DM. Many adults with DM have normal intelligence, although they may experience difficulties with concentration, memory, or executive functioning. Children with congenital or childhood-onset DM1 are more likely to have learning disabilities or developmental delays.
Can exercise help people with myotonic dystrophy?
Regular low-impact exercise and physical therapy may help maintain muscle strength, flexibility, and mobility. However, exercise plans should be made according to the individual’s abilities and supervised by a healthcare professional to prevent or avoid injuries.
Are heart problems common in people with myotonic dystrophy?
Yes, myotonic dystrophy can affect the electrical system of the heart, leading to abnormal heart rhythms and conduction problems. Regular cardiac evaluations, including electrocardiograms (EKGs), are important to detect and manage these complications early.
Can myotonic dystrophy cause breathing problems?
Weakness of the respiratory muscles can make breathing less effective. Sometimes, people may also develop sleep-related breathing disorders, such as obstructive sleep apnea. These problems can increase the risk of respiratory infections and may require treatments such as CPAP therapy or other respiratory support.
Is there ongoing research for new myotonic dystrophy treatments?
Yes. Researchers continue to study gene-targeted therapies, RNA-based treatments, and other approaches that may slow disease progression or address the underlying genetic abnormalities. While no cure is currently available, ongoing clinical research offers hope for more effective treatments in the future. If you have additional questions, ask your healthcare provider.
