What is Myotonic Dystrophy?

Myotonic dystrophy (DM), a type of muscle disease that typically starts in adulthood, is the most common form of muscular dystrophy. There are two main types of myotonic dystrophy: type I (DM1), also known as Steinert disease, and type II (DM2), also referred to as proximal myotonic myopathy. DM2 typically poses less severe symptoms compared to DM1. These disorders, which worsen over time, can affect multiple systems in the body and are caused by genetic defects.

The symptoms of these conditions are quite varied and can include anything from unnoticed muscle stiffness to severe weakness and disability. Some people also suffer from heart conduction problems, fertility issues, cataracts (clouding of the lens in the eye), and resistance to insulin, a hormone that regulates blood sugar levels. A congenital (present from birth) form of type I myotonic dystrophy is linked with noticeable developmental disabilities.

Myotonia, a key characteristic of these diseases, is a condition where muscles cannot relax immediately after contraction or tensing, because of repeated electrical activity of muscle fibers. In the context of myotonic dystrophy, physical activity can help to improve myotonia, but exposure to cold might make it worse.

What Causes Myotonic Dystrophy?

Myotonias are genetic conditions that can be passed down from one generation to the next. One common feature of myotonias is that they are often inherited in an autosomal dominant manner, which means that if one parent has the disease, there’s a 50% chance that each of their children will also have the disease.

There are two main types of myotonias: DM1 and DM2. Both are caused by a sort of “stutter” in a section of your DNA. This stutter, or expansion of DNA tandem repeats as it’s technically known, leads to an excess of RNA – a kind of genetic material – which causes the disease. The actual location and sequence of this DNA “stutter” differs between DM1 and DM2, which makes them distinct from each other.

DM1 is caused by an expansion of a specific sequence (cytosine-thymine-guanine, or CTG) in a gene on chromosome 19, called the DM1 protein kinase (DMPK) gene. On the other hand, DM2 is caused by an expansion of a different sequence (cytosine-cytosine-thymine-guanine, or CCTG) in another gene found on chromosome 3, known as the CCHC-type zinc finger nucleic acid-binding protein (CNB or ZNF9) gene.

In short, myotonias are genetic diseases caused by specific changes in your DNA, which lead to the production of excess RNA and trigger the symptoms of the disease.

Risk Factors and Frequency for Myotonic Dystrophy

Myotonic dystrophy is a type of muscle disorder that is mostly seen in people of European descent. There are two types, DM1 and DM2, with DM1 being more common. On average, one out of every 3000 people worldwide has this condition, although in some places, like Quebec, it is even more common, with one out of every 500 people being affected.

Signs and Symptoms of Myotonic Dystrophy

Myotonic dystrophy is a condition in which the muscles, eyes, heart, central nervous system, and certain parts of the endocrine system are affected. The intensity and pattern of symptoms can greatly vary, depending on the number of genetic repeats (CTG repeats) a person has. The disease can range from severe in infants to milder forms seen in adults. This condition is usually grouped into five categories: Congenital, Mild, Classic, Childhood, and Myotonic Dystrophy Type II.

Congenital Myotonic Dystrophy: This severe type occurs in about 15% of all cases, where the fetus shows signs of muscle and central nervous system complications. After birth, these infants may have unusual facial expressions and speech issues due to muscle weakness. The primary concern in these cases is respiratory problems, which are the leading cause of death in this period.
Mild Myotonic Dystrophy: The mild form typically begins between the ages of 20 to 70, usually after the age of 40. Symptoms include mild weakness, muscle stiffness, and cataracts. The individuals with this form have a normal life expectancy.
Classic Myotonic Dystrophy: The classic form generally appears during the 2nd, 3rd, or 4th decades of life. The distinguishing symptom is myotonia, characterized by muscle stiffness that eases with exercise. Other symptoms include impaired hand mobility and difficult walking due to foot drop. Individuals with this form may also present facial muscle weakness, causing a characteristic “hatchet face”. Heart issues are another concern for this group, and life expectancy is typically shortened.
Childhood Myotonic Dystrophy: This subtype typically begins around age 10. Early symptoms mostly revolve around cognitive and emotional difficulties. Speech slurring and hand muscle stiffness may also be prominent, possibly hampering learning. Heart conditions may also develop at this age.
Myotonic Dystrophy Type II: The second type of Myotonic Dystrophy usually appears in adulthood, with the median age being 48. Symptoms include early-onset cataracts (occurring before age 50), varying grip muscle stiffness, proximal muscle weakness, hearing loss, and muscle pain. The pain can fluctuate and is sometimes mistaken for fibromyalgia.

Testing for Myotonic Dystrophy

If you’re experiencing symptoms of weakness and have a family history of myotonic dystrophy (also known as DM), your doctor may suspect you have the condition. Several tests can help confirm the diagnosis, including genetic testing, blood tests, muscle biopsies, and electrocardiograms (to check for heart issues).

Genetic testing is especially useful, as it can reveal changes (called CTG repeats) in a specific gene linked to myotonic dystrophy. If the test shows more than 50 such repeats, it’s a clear indication of the disease. If the test is negative but your doctor still suspects myotonic dystrophy based on your symptoms, they might recommend additional genetic testing for changes (CCTG repeats) in another gene.

Creatine kinase is a substance often found in higher amounts in people with muscle diseases, but it may be normal in people with mild myotonic dystrophy. Blood tests may also reveal higher levels of certain liver enzymes in 30% to 50% of patients with myotonic dystrophy, although this doesn’t necessarily correlate with the severity of muscle weakness or the duration of the disease.

Electrodiagnostic testing is a method that can help detect myotonic dystrophy, even in those who do not have any symptoms. It involves passing a small amount of electrical current through the nerves and muscles to measure their activity and responsiveness. This test tends to show decreased amplitude in motor nerves conduction studies with normal latency and normal conduction velocities. Sensory nerve conduction studies typically come out normal. Bursts of spontaneous discharges (myotonic discharges) can be observed in the study, which is highly specific for the disease.

Finally, a muscle biopsy (which involves removing a small piece of muscle tissue for examination under a microscope) can reveal changes associated with myotonic dystrophy, such as irregular muscle fiber size, the presence of internal nuclei in rows, muscle scarring, and altered myofibril orientation (the pattern of muscle fibers).

Treatment Options for Myotonic Dystrophy

While there’s no cure for DM (also known as Myotonic Dystrophy), the aim is to help the patient maintain their health and independence as much as possible. This involves constant monitoring and treatment of all the health issues associated with DM.

Medical treatment involves the following procedures:

For heart health, a 12-lead electrocardiogram – a test that checks your heart’s electrical activity – is recommended annually. This helps to keep an eye on any changes in the heart’s conduction, or how it sends signals around the body. Regular heart imaging is also beneficial.

Pulmonary function tests help to monitor breathing problems related to neuromuscular respiratory failure. Therefore, regular tests to check lung function are suggested as well.

Daytime sleepiness and sleep apnea, which is a condition that causes pauses in breathing or shallow breaths while you sleep, can be an issue for DM patients. Health care providers recommend testing for sleep apnea and if needed, treatment with a continuous positive airway pressure (CPAP) machine, which helps you breathe more easily at night. Medicine like methylphenidate may be used to help with excessive sleepiness.

Yearly eye exams, including a detailed checkup using a slit-lamp (a special microscope), could help detect eye issues early. If a patient has cataracts that affect their vision, surgery can be considered for removal.

Pregnant patients or those thinking of getting pregnant need special care due to increased risks including miscarriage and complications during childbirth.

DM patients are more prone to conditions like diabetes and low thyroid function. It is vital to have regular tests to check their blood sugar levels and thyroid function. Men with DM often experience difficulty getting or maintaining an erection (erectile dysfunction) due to low levels of the hormone testosterone. Regular checks and treatment for low testosterone can improve this condition.

Medicines might be used to reduce muscle stiffness (myotonia). These could include drugs like mexiletine (a type of sodium channel blocker), certain antidepressants, benzodiazepines, or calcium antagonists. However, sodium channel blockers shouldn’t be given to patients with certain types of heart block.

Physical and occupational therapy can be beneficial. They can focus on improving muscle strength, evaluating the need for orthotics – devices that support or correct the function of a limb – and assessing whether you might benefit from other medical equipment. For issues related to speaking or swallowing, speech-language pathology (SLP) can help. SLP is also helpful for managing intellectual disabilities and learning new strategies to cope up with DM complications.

Schwartz-Jampel Syndrome is a unique disorder resulting from mutations in a particular gene (HSPG2). Patients don’t experience a gradual increase in muscle stiffness, nor do they show variable patterns of muscle stiffness during nerve tests, unlike in other muscle diseases.

Hyperkalemic Periodic Paralysis (HPP) is another condition that is caused due to gene mutations, specifically in a protein that controls muscle sodium channels. It involves occasional episodes of muscle weakness that begins usually in childhood and mostly lasts less than an hour. Certain triggers such as skipping meals, consuming food high in potassium, cold temperatures, or resting after exercise can worsen these bouts of weakness. Strength tests performed after giving potassium can trigger an episode.

Paramyotonia Congenita (PC) patients experience worsening muscle stiffness with repetitive muscle contractions and exercise, and also when their muscles are cold. This condition, caused by mutations in a particular gene (SCN4A), tends to start in early childhood and affects mainly the muscles of the face and upper body, with the lower body being less affected.

Myotonia Congenita is a genetic disorder caused by mutations in a gene (CLCN1) that determines the function of chloride channels in our muscles. It can be passed down in families in either of two patterns (Becker disease and Thomsen disease), with the former usually being more severe.

Several other conditions can show changes in muscle electrical activity but without obvious muscle stiffness. Below are some of these conditions:

Myotubular myopathy
Acid maltase deficiency
Debrancher deficiency
Inflammatory myopathies
Hypothyroid myopathy
Chloroquine myopathy
Statin myopathy
Cyclosporine myopathy

What to expect with Myotonic Dystrophy

The future health outcome of myotonic dystrophy, a type of muscle disease, is linked with the age when the symptoms first appear and the growth of certain genetic markers known as CTG repeats. The earlier the symptoms start and the more these genetic markers grow, the worse the health outcomes can be, and it could also affect the length of a person’s life.

Up to 50% of those with DM1, a specific type of this disease, might need to use a wheelchair or other forms of assistance for mobility before they die. On the other hand, those with DM2, another type of the disease, usually have a less severe experience and often don’t need to use medical equipment or aids for mobility.

The main cause of death in people with myotonic dystrophy is a failure in the muscles that control breathing due to the disease. This is followed by complications related to the heart.

Possible Complications When Diagnosed with Myotonic Dystrophy

DM, or myotonic dystrophy, is a condition which leads to issues in many different body systems, not just the muscles. Body systems impacted by DM will be prone to various complications.

Issues regarding the brain and nerves:

Not everyone who has DM experiences learning disabilities, but they are more common in certain types. They are most typically seen in people who have had DM since birth.
DM can increase the risk of stroke.
It’s common for DM patients to experience stress and sadness because they lose their ability to perform certain tasks.
DM sufferers often have problems with their sleep patterns, which can lead to excessive sleepiness during the day and sleep-disordered breathing during the night.
Ventriculomegaly, a condition where the chambers of the brain are larger than normal, can occur in those with congenital DM.

Eye related issues:

Almost all people with DM develop cataracts relatively early in life, usually in their 40s. They might also have hyperopia (farsightedness) and astigmatism (blurred vision).

Heart related issues:

More than half of DM patients develop heart problems, which can appear even before muscle symptoms. They might experience abnormal heart rhythms, heart muscle disease, and early-onset heart failure.

Lung related issues:

People with DM are prone to pneumonia due to loss of lung function. They also have a higher risk of complications related to anesthesia.

Digestive system issues:

Patients with DM might have trouble swallowing due to facial muscle and throat problems. As a result, they are at a greater risk of choking.
There is a higher incidence of gallstones and gallbladder inflammation because of increased gallbladder tension.
Unexplained liver issues, such as high liver enzyme levels, are also associated with DM.
Post-anesthesia aspiration, where food or liquid enters the lungs instead of the stomach, may occur due to weak throat muscles.

Hormonal system related complications:

DM patients might develop insulin resistance.
Men may experience fertility issues due to damage to the tissues of the testicles, while women might have increased risk of miscarriage, pre-term birth, and painful periods.

Skin related complications:

DM can cause male-pattern hair loss, and increase the risk of skin cancer and benign skin tumors.

Muscle and bone related complications:

A person with DM can lose motor function over time, which can increase the dependency on a wheelchair as the disease progresses.
Regular daily tasks can become difficult due to muscle weakness in the hands and ankles.
Pain in the muscles is a common symptom among DM patients.

Preventing Myotonic Dystrophy

Patients need to understand the importance of keeping their body strong and learning how to manage episodes of muscle stiffness or weakness, also known as myotonic episodes. It’s equally important for people who have Myotonic dystrophy (DM), especially men, to learn about strategies for preserving fertility. If they want to have children, they should also be advised about how DM is passed down through families.

Frequently asked questions

The prognosis for Myotonic Dystrophy depends on the age of symptom onset and the growth of genetic markers known as CTG repeats. Generally, the earlier the symptoms start and the more these genetic markers grow, the worse the health outcomes can be. Up to 50% of individuals with DM1 might require mobility aids before death, while those with DM2 usually have a less severe experience and may not need medical equipment or aids for mobility. The main cause of death in people with Myotonic Dystrophy is respiratory muscle failure, followed by complications related to the heart.

Myotonic Dystrophy is a genetic condition that is inherited in an autosomal dominant manner. It is caused by specific changes in DNA, which lead to the production of excess RNA and trigger the symptoms of the disease.

Signs and symptoms of Myotonic Dystrophy can vary depending on the type and severity of the condition. Here are the signs and symptoms associated with each subtype: 1. Congenital Myotonic Dystrophy: - Muscle and central nervous system complications in the fetus - Unusual facial expressions and speech issues in infants - Respiratory problems, which are the leading cause of death in this period 2. Mild Myotonic Dystrophy: - Mild weakness and muscle stiffness - Cataracts - Normal life expectancy 3. Classic Myotonic Dystrophy: - Myotonia, characterized by muscle stiffness that eases with exercise - Impaired hand mobility and difficult walking due to foot drop - Facial muscle weakness, causing a characteristic "hatchet face" - Heart issues - Shortened life expectancy 4. Childhood Myotonic Dystrophy: - Cognitive and emotional difficulties - Speech slurring - Hand muscle stiffness - Learning difficulties - Heart conditions 5. Myotonic Dystrophy Type II: - Early-onset cataracts (occurring before age 50) - Varying grip muscle stiffness - Proximal muscle weakness - Hearing loss - Muscle pain, which can fluctuate and is sometimes mistaken for fibromyalgia It's important to note that the intensity and pattern of symptoms can greatly vary, and individuals may experience a combination of these symptoms.

The types of tests needed for Myotonic Dystrophy include: - Genetic testing to check for changes in specific genes linked to myotonic dystrophy, such as CTG repeats. - Blood tests to measure levels of creatine kinase and certain liver enzymes. - Electrocardiograms (ECGs) to check for heart issues. - Electrodiagnostic testing to measure nerve and muscle activity. - Muscle biopsy to examine muscle tissue for changes associated with myotonic dystrophy.

Myotubular myopathy, Acid maltase deficiency, Debrancher deficiency, Inflammatory myopathies, Hypothyroid myopathy, Chloroquine myopathy, Statin myopathy, Cyclosporine myopathy.

When treating Myotonic Dystrophy, there can be several side effects and complications. These include: - Heart issues: abnormal heart rhythms, heart muscle disease, and early-onset heart failure. - Lung problems: pneumonia, higher risk of complications related to anesthesia. - Digestive system complications: trouble swallowing, higher risk of choking, gallstones, gallbladder inflammation, unexplained liver issues, and post-anesthesia aspiration. - Hormonal system complications: insulin resistance, fertility issues in men, increased risk of miscarriage, pre-term birth, and painful periods in women. - Skin complications: male-pattern hair loss, increased risk of skin cancer and benign skin tumors. - Brain and nerve issues: learning disabilities, increased risk of stroke, stress and sadness, sleep problems, and ventriculomegaly. - Eye issues: cataracts, hyperopia, and astigmatism. - Muscle and bone complications: loss of motor function, muscle weakness in the hands and ankles, and muscle pain. It is important to note that not all patients will experience all of these side effects, and the severity can vary. Treatment for Myotonic Dystrophy aims to manage and minimize these complications to maintain the patient's health and independence.

A neurologist or a geneticist.

On average, one out of every 3000 people worldwide has this condition.

Myotonic Dystrophy is treated through a combination of medical procedures and therapies. Medical treatment involves regular monitoring and treatment of health issues associated with DM, such as heart health, pulmonary function, sleep apnea, eye exams, blood sugar levels, thyroid function, and testosterone levels. Medications may be used to reduce muscle stiffness. Physical and occupational therapy can help improve muscle strength and assess the need for orthotics or other medical equipment. Speech-language pathology can assist with speaking, swallowing, managing intellectual disabilities, and learning strategies to cope with DM complications.

Myotonic dystrophy is a type of muscle disease that is the most common form of muscular dystrophy. It has two main types: type I (DM1) and type II (DM2), with DM2 typically having less severe symptoms compared to DM1. These disorders worsen over time and can affect multiple systems in the body, and they are caused by genetic defects.

Genetic Disorder Joint Muscle and Bone Muscular Dystrophy Myotonic Dystrophy