Patient Information: Myotonic Dystrophy
WHAT IS MYOTONIC DYSTROPHY?
Myotonic dystrophy, also known as Steinerts’s disease, is the most frequently diagnosed adult form of muscular dystrophy. It is characterized primarily by progressive muscle weakness and muscle wasting and by myotonia (difficulty in relaxing a muscle or a group of muscles following contraction). It is a multisystem disease, typically involving a wide range of other tissues as well as muscle.
WHO CAN BE AFFECTED BY MYOTONIC DYSTROPHY?
Myotonic dystrophy is a hereditary disorder transmitted from generation to generation by a parent who has the disorder. Myotonic dystrophy can affect either males or females.
Approximately one person in 8,000 around the world is affected by myotonic dystrophy, but it occurs more frequently in some populations than in other. For example, in northern Quebec the incidence of myotonic dystrophy is exceptionally high, with up to one person in 500 being affected.
AT WHAT AGE CAN A PERSON BE AFFECTED?
Myotonic dystrophy can occur at any age, though a high percentage of affected people are diagnosed by their early twenties. An unusual feature of myotonic dystrophy is known as anticipation. Anticipation refers to the tendency for myotonic dystrophy to become more severe and the age at which symptoms appear to occur earlier as it passes down the generations of a family.
Congenital myotonic dystrophy is the most severe form of myotonic dystrophy. Symptoms of this form of myotonic dystrophy are always evident at birth. In fact, decreased movements may be noted in the unborn child as early as the second trimester of pregnancy. Virtually all infants with congenital myotonic dystrophy are born to mothers who also have myotonic dystrophy.
IS MYOTONIC DYSTROPHY ANYONE’S FAULT?
No. myotonic dystrophy is a genetic disorder that is passed from one generation to next. It is not anyone’s fault.
IS IT CONTAGIOUS?
No. genetic diseases are not contagious.
WHAT CAUSES MYOTONIC DYSTROPHY?
Myotonic dystrophy is caused by a mutation in a gene located on the log arm of chromosome 19.
In 1992, the gene responsible by Dr. Robert Korneluk and his Canadian research team, in collaboration with groups in the Netherland, California and Britain. These distinguished scientists are continuing their research to determine exactly how, when faulty, it causes myotonic dystrophy.
HOW DO GENE ABNORMALITIES CAUSE MYOTONIC DYSTROPHY?
The basic fault is an unstable inherited mutation in a particular gene known as the myotonic dystrophy protein kinase gene. At the present time, it is not known how the genetic abnormality causes the disorder.
WHAT ARE GENES?
Genes are basic function units of heredity that tell the cells and tissues of the body what specialized functions they will perform. They are found in the nucleus of the cell as tiny segments of DNA in the chromosome.
There are approximately 80,000 individual genes located on the 46 chromosomes (23 pairs) inside each of the billons of cells within the human body.
HOW DO GENES FUNCTION?
Genes are the blueprints for structure and function. Each gene carries the code that directs the cell to make a specific protein. Proteins are the molecules that carry out all of the work of the living body. The proteins coded by the genes are responsible for all structures and functions of living cells from eye colour to muscle function. They can also be hormones or enzymes within the body.
WHERE DO THE FAULTY GENES COME FROM?
When a baby is formed, he/she receives 23 chromosomes from each parent, for total of 46 chromosomes (23 pairs). Normally, each pair of chromosomes carries the same genes for the same traits. 22 pairs of the chromosomes are called autosomal chromosomes, which simply means that they are identical in both males and females. The chromosomes in the 23rd pair are known as the sex chromosomes and it is here that the sex of the unborn child is determined. Genes are found packed together on these chromosomes. Each gene has a precise location on one of them. For reasons that are only partly understood, one or more genes may become flawed or lost, and a serious disorder may result.
Depending on the type of neuromuscular disorder, the faulty or missing gene may be inherited. Also, the way that the disorder is inherited will vary from disorder to disorder.
HOW IS MYOTONIC DYSTROPHY INHERITED?
Myotonic dystrophy is transmitted through autosomal dominant inheritance. Autosomal refers to the fact that the faulty gene can appear on any of the 22 chromosome pairs not associated with determining the sex of the child. In case of myotonic dystrophy, the faulty gene is found on chromosome 19.
Dominant refers to fact that the disorder is passed down from a parent of either sex who has the disorder. With each pregnancy, there is a 50% risk that the child will receive the faulty gene from the affected parent and have myotonic dystrophy. There is a 50% chance that he/she will receive normal versions of the gene from each parent and will therefore be unaffected.
WHAT ARE THE DIFFERENT FORMS OF MYOTONIC DYSTROPHY?
There are forms of myotonic dystrophy. They are the adult form and the congenital form.
This form generally becomes apparent when a person is between 10 and 30 years old. But in some cases, symptoms may appear in younger children or much later in life.
The course of myotonic dystrophy varies widely form one person to the next, even among members of the same family. Some people with the disorder have such mild symptoms that they do not suspect anything wrong and adapt very easily. Others may be faced with a significant level of disability, requiring assistance with mobility and activities of daily living.
In the adult form of myotonic dystrophy, muscle weakness usually starts gradually and progresses slowly. People with this form often mention stiffness as an early symptom. Disability typically occurs 15 to 20 years after the onset of the disease when the weakness affect the shoulder muscles, thighs and hips, though many people with myotonic dystrophy live their entries lives without any detectable symptoms.
HOW ARE MUSCLES AFFECTED?
In the adult form of myotonic dystrophy, muscle weakness is reported by over 60% of clients. It is the most common symptom resulting in referral to a physician. Hands and feet are normally the first parts of the body to be affected. Weakness may then spread gradually into the muscles of face, neck, arms and legs.
The following signs of muscles weakness may be present in affected individuals:
- Drooping eyelids, and along, rather expressionless face
- Unclear pronunciation of words
- Difficulty raising the head when lying down
Quite often, premature baldness may occur on the forehead and top of the head in males and women may experience abnormal thinning of their hair.
WHAT OTHER SYPMTOMS MAY BE EXPERIENCED?
Sleep and personality: Many people with myotonic dystrophy tend to fall asleep easily, sleep for long periods of time and feel excessively drowsy while awake. This characteristic is known as somnolence. It may be so noticeable that it affects an individual’s ability to hold a job. Individuals affected by myotonic dystrophy may be very easy going or at times they may be listless. They are often content to remain inactive for long periods of time.
Work: As a person’s myotonic dystrophy progresses, the individual may experience difficulty in performing manual tasks or maintaining a good pace at work. Reorganizing or restructuring responsibilities on the job may help the person to remain active and productive for a longer time.
Reaction to Drugs: People with myotonic dystrophy may react in unusual ways to certain drugs. It is better to refrain from taking any non-prescription drug without the advice of a physician. Some people with myotonic dystrophy have an increased sensitivity to anesthetic agents and other muscle relaxants. Administration of these drugs might results in excessive drowsiness or other side effects. This sensitivity has been noted both in clients who are severely affected by myotonic dystrophy and in those whose symptoms are mild.
HOW IS MYOTONIC DYSTROPHY DIAGNOSED?
A diagnosis of myotonic dystrophy is made by a physician. A physical examination and a complete history are necessary for a doctor to assess the presence of myotonia, muscle weakness and any decrease in muscle size. Details of a positive family history, if present, will be investigated, as well as the history of the client’s present concerns.
Diagnostic tests are also used by the physician in making a positive diagnosis of myotonic dystrophy.
WHAT DIAGNOSTIC TESTS ARE PERFORMED?
- DNA Analysis performed on a sample of blood is a valuable diagnostic tool. This genetic test is used to make the diagnosis of myotonic dystrophy more exact. It identifies the presence or absence of the genetic fault that is responsible for myotonic dystrophy. Where there is a positive family history, the use of this test during pregnancy can also determine whether or not a fetus is affected by myotonic dystrophy.
- An electromyogram (EMG), a test designed to measure and record electrical activity in muscles, is useful in diagnosing many disorders affecting muscle. Electrodes are attached to the body in a painless procedure. Accurate descriptions of muscle activity provide evidence of the presence or absence of myotonic dystrophy.
- A muscle biopsy is necessary whenever a physician wants to clarify the diagnosis. A sample muscle tissue is examined under a microscope for changes characteristic of myotonic dystrophy.
- An eye examination can identify the opacities seen in the lens of a person who has cataracts. The presence of cataracts may be the first or in some cases, the only symptoms seen in a person with myotonic dystrophy. This information is important for diagnosis as well as for management.
WHERE CAN ADVICE BE OBTAINED?
Neurologists, doctors who specialize in disorders affecting the nervous system, are often consulted for patients who may have myotonic dystrophy. Nerves and muscles are part of the so-called peripheral nervous system.
Neuromuscular clinics and hospital across Canada are equipped to do the necessary diagnostic testing and to offer advice and support regarding the ongoing management of myotonic dystrophy.
Geneticists, doctors who specialize in medical genetics, molecular geneticists and genetic counselors are employed by major hospitals across Canada and are available to patients and their families for the purpose of diagnosis and counselling. A geneticists or a genetic counselor will be able to advise family members about their risk of having an affected child in families where there is a positive history of myotonic dystrophy.
IS THERE A TREATMENT OR CURE AVAILABLE FOR MYOTONIC DYSTROPHY?
At the present time, there is no cure or treatment available that can prevent or delay the progression of muscle weakness caused by myotonic dystrophy.
Staying as active as possible remains the most effective way of maintaining the best physical condition. Rehabilitation specialists (physiotherapist and occupational therapists) can advise individuals affected by myotonic dystrophy and their families on how to create a stimulating environment. Also, they can prescribe an exercise program and aids that can assist an individual to carry out activities of daily living.
There are medications available that can decrease the effects of myotonia, but they sometimes cause undesirable side effects. Drugs are usually prescribed only when myotonia prevents a person from working or performing daily activities.
When necessary, surgery is available to clients who have cataracts. The operation, that may require a short stay in hospital, can result in substantially improved vision.
Speech therapy can provide assistance to a child or adult who has difficulty speaking. An adapted educational environment can promote the development of a child’s abilities within school setting.
Arrhythmias, dizziness and other symptoms associated with heart problems may be treated with medication when they are causing difficulties.
If cold lasts for more than two weeks, treatment may be indicated. As well, some people may find it useful to be vaccinated against the flu
Digestive problems may be decreased by attention to healthy eating habits. Some general suggestions include:
- Eating three meals a day at regular hours,
- Drinking plenty of liquids such as water, fruit juice and milk),
- Eating fibre-rich foods such as whole grain cereals, vegetables and fruit,
- Avoiding very cold foods such as ice cream and iced drinks and
- Chewing food slowly and well.
If problems with constipation or stomach irritation persist, medical treatment based on the individual’s complaints may be necessary.
GENERAL INFROMATION FOR THE PERSON WITH MYOTONIC DYSTROPHY
- Always remember to inform doctors, dentists and other health professionals that you have myotonic dystrophy.
- Your health problems may not all be caused by myotonic dystrophy. Try to deal with a family doctor who knows you well.
- Before becoming pregnant, consult your doctor. Tests and counseling are available to help you to determine the risks involved.
- Regular physical activity and good eating habits will help protect your health and improve the quality of your life.
WHO ARE THE MEMBERS THE HEALTH TEAM?
A family will be seen by their own family doctor and possibly, other health professionals. If necessary, they will be referred to a neuromuscular clinic as near to their home as possible.
Treatment, if any, will vary according to the severity of weakness and the related problems that a person is experiencing. Because the course of myotonic dystrophy is so variable, even among members of the same family, it is difficult to be specific about who will need to be consulted. The following information is intended to serve as a guide to medical professionals with whom you may be in contact.
The physician (PT) will teach chest physiotherapy techniques to children and adults that will enhance their physical wellness. The physiotherapist helps clients develop individual exercise programs to maintain optimum muscle strength. This program will include the and amount of activity that is best for each person. The PT may also be consulted should respiratory difficulties occur.
The geneticist will help individuals and their families to understand how this disorder has been transmitted within their family, as well as the impact of myotonic dystrophy on future generations.
The occupational therapist (OT) can help clients learn how to adapt to physical limitation. The OT will be involved, as required, in choosing equipment and to enhance function at school or in the workplace.
In conjunction with an infant development worker, the OT/PT may have suggestions for activities to stimulate intellectual development of babies and children with myotonic dystrophy.
The role of the nurse, whether in the clinic or the community, is to work with the family to understand the disorder and its management.
The social worker, in conjunction with the nurse, provides support to the individual and family member coping with the effects of myotonic dystrophy.