The muscular dystrophies correspond to a family of diseases characterized by muscle weakness and progressive degeneration of the muscles of the body of fibers. The muscles atrophy gradually, that is to say, they lose their volume and therefore, their strength.
These are diseases of genetic origin that can occur at any age: from birth, during childhood or in adulthood. There are more than 30 forms that differ in age of onset of symptoms, nature of affected muscles and severity. Most muscular dystrophies become progressively worse. At present, there is still no cure. The best known and most common type of muscular dystrophy is Duchenne muscular dystrophy , also known as Duchenne muscular dystrophy.
In muscular dystrophy, the muscles affected in muscular dystrophy are mainly those that allow voluntary movements , including muscles, thighs, legs, arms and forearms . In some dystrophies, the respiratory muscles and the heart can be affected. People with muscular dystrophy can gradually lose their mobility when walking. Other symptoms may be associated with muscle weakness, including heart, gastrointestinal, eye problems …
Dystrophy or myopathy? The term “myopathy” is the generic name for all muscular pathologies characterized by an attack of muscle fibers. Muscular dystrophies are special forms of myopathies. But in everyday language, the term myopathy is often used to refer to muscular dystrophy.
The muscular dystrophies are part of rare and orphan diseases. It is difficult to know the exact frequency, since it brings together different diseases. Some studies estimate that about 1 in 3,500 people have it.
For exemple :
- The Duchenne muscular dystrophy 1 Duchenne affects about one boy in 3500.
- Becker’s myopathy concerns 1 boy out of 18,000 ,
- Facio-scapulohumeral dystrophy affects about 1 in 20,000 people.
- The disease Emery-Dreifuss , affects 1 in 300 000 causes retraction of the tendon and an infringement of the heart muscle
Some muscular dystrophies are more common in some parts of the world. So :
- Congenital myopathy, known as Fukuyama, concerns mainly Japan.
- In Quebec, however, oculopharyngeal muscular dystrophy dominates (1 case per 1,000 people), whereas it is very rare in the rest of the world (1 case per 100,000 on average). as its name indicates, this disease mainly affects the muscles of the eyelids and throat.
- For its part, Steinert’s disease or “myotonia Steinert” is widespread in the Saguenay-Lac St-Jean region, where it affects about 1 in 500 people.
- The sarcoglycanopathies are more common in North Africa and relate to one in 200,000 in the North East of Italy .
- Calpainopathies were first described on the island of Reunion. One in 200,000 is affected.
Causes of Muscular dystrophies
The muscular dystrophies are genetic diseases , that is to say, they are due to a defect (or mutation) of a gene necessary for the proper functioning of muscles or development. When this gene is mutated, the muscles can no longer contract normally, they lose their vigor and atrophy.
Several dozens of different genes are involved in muscular dystrophies. Most often, these are genes that “make” proteins located in the membrane of muscle cells 3 .
For exemple :
- Duchenne muscular dystrophy muscular dystrophy is linked to a deficiency of dystrophin , a protein located under the membrane of muscle cells and which plays a role in the contraction of the muscle.
- In nearly half of the congenital muscular dystrophies (which appear at birth), it is a deficiency of merosin , a constituent of the membrane of the cells of the muscle, which is in question.
Like many genetic diseases , muscular dystrophies are most often transmitted by parents to their child. More rarely, they can also “appear” spontaneously, when a gene mutates accidentally. In this case, the diseased gene is not present in the parents or other members of the family.
Most of the time, muscular dystrophy is transmitted recessively . In other words, for the disease to be expressed, both parents must be carriers and transmit the abnormal gene to the child. But the disease is not manifested in the parents, because each one carries only one abnormal parental gene and not two abnormal parent genes. However, a single normal gene is enough for the muscles to function normally.
In addition, some dystrophies only affect boys : this is the case of Duchenne myopathies and Becker’s myopathy. In both cases, the gene involved in these two diseases is located on the X chromosome that exists in a single copy in males.
Two big families
There are usually two major families of muscular dystrophies:
– the muscular dystrophies called congenital (DMC), which appear in the first 6 months of life. There are about ten forms of variable severity, including DMC with primary merosin deficiency, Ullrich’s DMC, stiff-column syndrome, and Walker-Warburg syndrome;
– Muscular dystrophies appearing later in childhood or adulthood , as examples:
- Duchenne muscular dystrophy
- Becker’s myopathy
- Emery-Dreyfuss myopathy (there are several forms)
- Facio-scapulo-humeral myopathy, also called Landouzy-Dejerine myopathy
- Myopathies belts, so called, because they affect especially the muscles around the shoulders and hips.
- Myotonic dystrophies (types I and II), which includes Steinert’s disease. They are characterized by a myotonia , that is to say that the muscles do not manage to relax normally after a contraction.
- Oculopharyngeal myopathy
The evolution of muscular dystrophies varies greatly from one form to another, but also from one person to another. Some forms evolve rapidly, leading to early loss of mobility and walking and sometimes fatal cardiac or respiratory complications, while others evolve very slowly over decades. Most congenital muscular dystrophy, for example, changing little or even if the symptoms can be severe immediately.
Complications of Muscular dystrophies
The complications vary enormously depending on the type of muscular dystrophy. Some dystrophies can reach the respiratory muscles or the heart, with sometimes very serious consequences.
Thus, cardiac complications are quite common, especially in boys with Duchenne muscular dystrophy.
In addition, muscle degeneration causes the body and joints to deform little by little: sufferers can suffer from scoliosis . Muscle and tendon shortening is frequently observed, resulting in muscle (or tendon) retractions . These different attacks result in joint deformities: the feet and hands are turned inwards and downwards, knees or elbows are deformed …
Finally, it is common that the disease is accompanied by anxiety or depressive disorders that must be taken care of.
Symptoms of muscular dystrophies
Muscular dystrophies are all manifested by muscle weakness that tends to progressively worse, even the symptoms vary according to the type of muscular dystrophy . Depending on the case, other symptoms may be present, such as heart and respiratory disorders, eye abnormalities (malformations, cataracts), intellectual deficit, hormonal disorders, etc.
Characteristics of the most common muscular dystrophies:
- Duchenne’s myopathy :most often, symptoms begin around the age of 3 to 5 years. Due to the weakening of the leg muscles, children who had been walking “normally” fell frequently and have difficulty getting up. Running, walking and jumping becomes more and more difficult for them. The muscles lose volume as they weaken, with the exception of the calf muscles which can appear hypertrophied (by replacing muscle mass with fat). Children often complain of cramps and muscle aches. The disease evolves fairly quickly as soon as the first symptoms appear. The use of a wheelchair is generally required around the age of 12. Muscle retractions result in scoliosis and joint deformities. On the other hand, some affected children have a slight mental retardation. Towards the end of adolescence, cardiac complications often occur (heart failure), as well as respiratory problems requiring assisted ventilation. Life expectancy is decreased (from 20 to 30 years on average).
- Becker’s myopathy : the symptoms are comparable to those of Duchenne muscular dystrophy, but they are less marked and evolution is slower. Symptoms begin around 5 to 15 years of age, sometimes later, and are characterized by a progressive loss of muscle strength in the limbs and trunk. In more than half of the cases, walking remains possible until the age of about 40 years. On the other hand, cardiac involvement is frequent and may appear immediately.
- Steinert’s Disease : This is one of the 3 most common myopathies in adults, and the most common in Quebec. The symptoms are very variable from person to person. Although they usually appear around the age of 30 or 40, there are earlier forms (juvenile and congenital forms). Myotonia, an abnormally prolonged muscle contraction (the muscle relaxes too slowly), is especially present in the hands, and sometimes in the tongue. The muscles of the face can also be affected as well as the muscles of the neck and ankles. Cardiac and respiratory symptoms are often present and potentially serious. Digestive, respiratory, hormonal, ocular disorders as well as infertility, and early baldness are also common.
- Belt myopathies : Symptoms usually appear quite late in childhood or early adulthood (around age 20). The muscles of the shoulders and hips weaken gradually, while the muscles of the head and neck and the diaphragm are generally not affected. However, even if some forms are accompanied by respiratory impairment, it remains stable. Cardiac involvement is rare. Evolution is very variable, depending on the form.
- Myopathie facio-scapulo-humérale (maladie de Déjerine-Landouzy) : the symptoms usually appear late in childhood or in adulthood (around 10 to 40 years). As the name suggests, it mostly affects the muscles of the face, shoulders and arms. Thus, it becomes difficult to sketch a smile, to whistle and to close your eyes. The loss of mobility occurs in about 20% of cases. The disease is slowly evolving and life expectancy is normal.
- Congenital muscular dystrophies. Symptoms vary from one form to another, but are present at birth or in the first months of life. The baby has little muscle tone (hypotonic), has difficulties to suck and swallow, sometimes even to breathe. These dystrophies can be accompanied by inter alia brain malformations, mental retardation, eye malformations.
- Oculo-pharyngeal myotonia : This disease is relatively common in Quebec. Symptoms usually appear around 40 or 50 years old. The first signs of the disease are manifested by drooping eyelids, followed by weakness of the muscles of the eyes, face and throat (pharynx), causing difficulty in swallowing food. The progression of the disease is slow.
Risk factors for Muscular dystrophies
- Family history of muscular dystrophy (parents, siblings …).
- Child already suffering from muscular dystrophy, who is afraid of a similar risk for other children to come.
If a person carries the gene for the disease, there is no way to prevent the onset of symptoms. Couples with a family history of the disease (cases of muscular dystrophy in the family or birth of a first child affected) may consult a genetic counselor (geneticist doctor or prenatal diagnosis specialist) to know the risk of giving birth to a child. sick child. Today, screening tests detect the disease, before birth or even before implantation of the embryo in the uterus (prenatal or preimplantation diagnosis). They also make it possible to know if it is about a genetic accident in the chromosomes of the child, whereas the parents do not carry the gene (the risk for a child to come is then normal).
Medical treatment of muscular dystrophies
There is still no effective drug treatment to cure muscular dystrophies or to curb their evolution. The goal of medical management is to limit joint and thoracic deformities and help patients to live as comfortable as possible. However, the different researches in gene therapy (replacement of defective genes by healthy genes) are very active in the field of muscular diseases and therefore represent a promising path for treatment in the years to come.
Physiotherapy and orthopedic treatments
Regular physiotherapy sessions are essential to help people in their daily lives. Monitoring in a rehabilitation center helps preserve mobility, maintain flexibility and limit muscle and joint pain, through a series of exercises and massages.
The evolution of the disease requires the wearing of equipment (or orthoses ) is often necessary to limit deformations:
- Wearing a corset to relieve the joints
- Cane or crutch, to compensate for pain or difficulty walking
- Wheelchair use is often needed later.
Finally, orthopedic surgery can be proposed as appropriate to correct joint deformities, including scoliosis, and improve the quality of life and respiratory function. In some cases limb surgeries also limit disability and maintain or prolong walking ability.
At present, no treatment can cure these diseases. Nevertheless, some medications can help relieve symptoms, such as muscle pain, cramps or myotonia. This is the case of diphenylhydantoin (Dilantin), mexiletine (Mexitil), baclofen (Liorésal), dantrolene (Dantrium) and carbamazepine (Tégrétol).
In addition, boys with Duchenne muscular dystrophy and sometimes Becker’s myopathy can benefit from treatment with corticosteroids (prednisone). The anti-inflammatory action of corticosteroids can slow the progression of the disease. However, this treatment has many side effects that sometimes make it difficult to bear. The most common side effects include excessive weight gain, decreased bone density (leading to fracture risk), high blood pressure, cataracts, and mood disorders. In the long term, the efficacy of corticosteroids in these two indications is uncertain.
Frequent in certain muscular dystrophies, cardiac disorders require appropriate follow-up and management. Angiotensin converting enzyme (ACE) inhibitors alone or in combination with beta-blockers, two classes of drugs commonly used to treat hypertension, have been shown to be effective in reducing heart failure in people with Duchenne muscular dystrophy
Another possible treatment for heart attacks is the use of eplerenone, a so-called “anti-aldosterone” medicine used in the management of heart failure. Other studies are underway to better evaluate the effectiveness of this treatment.
In addition, implantation of a pacemaker is sometimes indicated in people with severe heart rhythm disorders.
|Warning. Some drugs, such as diclofenac (Apo-Diclo, Arthrotec) can worsen heart failure. Consult your doctor before taking any new medicine.|
Respiratory muscle involvement is common, especially in Duchenne muscular dystrophy or Steinert’s disease. It results in difficulty breathing, shortness of breath, tiredness on waking or a weak cough. It may require the provision of respiratory assistance, especially at night. In severe cases, it is sometimes necessary to perform a tracheostomy, that is to say an opening in the trachea to provide ventilation.
|Food and nutrition
If corticosteroids can cause weight gain that makes movement even more difficult, severe muscular dystrophies often cause weight loss. In addition, impaired masticatory and swallowing muscles can make feeding difficult, as well as difficulty using weakened arms to eat. Hence the importance of avoiding undernutrition by taking the necessary measures, such as the use of suitable utensils, furniture of sufficient height and the consumption of soft foods. Sometimes dietary supplements are useful for maintaining a good nutritional status.
Muscular dystrophies – Complementary approaches
Creatine . This natural substance produced by the body is used in the manufacture of proteins. It is sold commercially as a dietary supplement, especially to help athletes to increase their muscle mass . In 2007, an analysis of 12 studies involving 266 people with myopathy showed that creatine administration, in the short or medium term, made it possible to increase muscle strength in patients. The opinion of the doctor is nevertheless necessary.
Coenzyme Q10. The results of two preliminary clinical trials have concluded the effectiveness of coenzyme Q10 supplementation (100 mg daily) to improve physical function for people with various forms of muscular dystrophy. However, this research carried out in 1995 did not have other consequences.