The muscular dystrophies correspond to a family of muscular diseases characterized by weakness and progressive muscular degeneration: fibers of the muscles of the body degenerate. The muscles gradually atrophy, that is to say, they lose their volume and therefore their strength.

Those are maladies Original genetic which can appear at any age: from birth, during childhood or even in adulthood. There are more than 30 forms that differ in the age of onset of symptoms, the nature of the muscles affected and the severity. Most muscular dystrophies get progressively worse. Currently, there is no cure yet. The best known and most common of muscular dystrophies is Duchenne muscular dystrophy, also called “Duchenne muscular dystrophy”.

In muscular dystrophy, the muscles affected in muscular dystrophy are mainly those that allow the voluntary movements, especially muscles, thighs, legs, arms and forearms. In some dystrophies, the respiratory muscles and the heart can be affected. People with muscular dystrophy may gradually lose their mobility when walking. Other symptoms can be associated with muscle weakness, in particular heart, gastrointestinal, eye problems, etc.

Prevalence

The muscular dystrophies are among the 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 people have it.

For exemple :

• La myopathy Duchenne¹ Duchenne¹affects about one in 3500 boys.
• Becker’s muscular dystrophy affects 1 in 18 boys²,
• Facioscapulohumeral dystrophy affects approximately 1 in 20 people.
• La maladie d’Emery-Dreifuss, affects 1 in 300 people and causes tendon retraction and heart muscle damage

Certain muscular dystrophies are more common in certain regions of the world. Thereby : 

• The so-called Fukuyama congenital myopathy mainly concerns Japan.
• In Quebec, on the other hand, it is oculopharyngeal muscular dystrophy which dominates (1 case per 1 people), while it is very rare in the rest of the world (000 case per 1 on average¹) As the name suggests, this disease mainly affects the muscles of the eyelids and throat.
• For its part, the Steinert’s disease or “Steinert’s myotonia”, is very common in the Saguenay-Lac St-Jean region, where it affects about 1 in 500 people.
• The sarcoglycanopathies are more common in North Africa and affect one in 200 people in northeastern Italy.
• Calpainopathies were first described in Reunion Island. One in 200 people is affected.

Causes

The muscular dystrophies are genetic diseases, that is to say that they are due to an anomaly (or mutation) of a gene necessary for the proper functioning of muscles or their development. When this gene is mutated, the muscles can no longer contract normally, they lose their vigor and atrophy.

Several dozen 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 myopathy is linked to a deficiency in dystrophine, a protein located under the membrane of muscle cells and which plays a role in muscle contraction.
• In almost half of congenital muscular dystrophies (which appear at birth), it is a deficiency in merosine, a constituent of the membrane of muscle cells, which is involved.

Like many genetic diseases, muscular dystrophies are most often transmitted by parents to their children. More rarely, they can also “appear” spontaneously, when a gene accidentally mutates. In this case, the diseased gene is not present in the parents or other family members.

Most of the time, the muscular dystrophy is transmitted in a way recessive. In other words, for the disease to be expressed, both parents must be carriers and pass the abnormal gene to the child. But the disease does not manifest itself in the parents, as each carries only one abnormal parental gene and not two abnormal parental genes. However, a single normal gene is enough for the muscles to function normally.

In addition, some dystrophies only affect the garçons : this is the case with Duchenne muscular dystrophy and Becker’s muscular dystrophy. In both cases, the gene involved in these two diseases is located on the X chromosome which exists in a single copy in males.

Two big families

There are generally two main families of muscular dystrophies:

– the muscular dystrophies say congenital (DMC), which appear in the first 6 months of life. There are about ten forms of it, of varying severity, including CMD with primary merosin deficiency, Ullrich’s CMD, stiff spine syndrome and Walker-Warburg syndrome;

– the muscular dystrophies appearing later in childhood or adulthood, as examples³ :

• Duchenne muscular dystrophy
• Becker’s myopathy
• Emery-Dreyfuss myopathy (there are several forms)
• Facioscapulo-humeral myopathy, also called Landouzy-Déjerine myopathy
• The myopathies of the girdles, so named, because they mainly affect the muscles located around the shoulders and the hips.
• Myotonic dystrophies (types I and II), including Steinert’s disease. They are characterized by a myotonie, that is, the muscles fail to relax normally after a contraction.
• Oculopharyngeal myopathy

Evolution

The evolution of muscular dystrophies is very variable from one form to another, but also from one person to another. Some forms evolve rapidly, leading to early loss of mobility and gait and sometimes fatal cardiac or respiratory complications, while others evolve very slowly over decades. Most congenital muscular dystrophies, for example, have little or no progress, although symptoms can be severe right away.³.

Complications

Complications vary greatly depending on the type of muscular dystrophy. Some dystrophies can affect the respiratory muscles or the heart, sometimes with very serious consequences.

Thus, heart complications are quite common, especially in boys with Duchenne muscular dystrophy.

In addition, the muscle degeneration causes the body and the joints to deform little by little: sufferers can suffer from scoliosis. Shortening of muscles and tendons is frequently observed, resulting in muscle retractions (or tendons). These various attacks result in joint deformities: the feet and hands are turned inwards and downwards, the knees or elbows are deformed …

Finally, it is common for the disease to be accompanied by anxiety or depressive disorders that need to be taken care of.