La myopathie de Bethlem est une maladie rare affectant les tissus conjonctifs et les muscles squelettiques provoquant une faiblesse musculaire et une raideur articulaire. La myopathie de Bethlem est une affection musculaire. Il s’agit d’une maladie héréditaire et elle porte le nom des médecins néerlandais Bethlem et van Jijngaarden, qui ont décrit la maladie pour la première fois en 1976. La myopathie de Bethlem est un type de dystrophie musculaire congénitale, bien qu’elle soit moins grave et progresse lentement par rapport aux autres maladies musculaires. conditions de dystrophie.
La maladie se présente avec des symptômes cliniques légers avec une faiblesse musculaire proximale ainsi que des contractures précoces des doigts. L’absence de cardiomyopathie et de mollets pseudohypertrophiques sont les caractéristiques distinctives de la myopathie de Bethlem. L’apparition de la maladie peut survenir à tout moment de la vie d’une personne, y compris in vitro également. Les gènes responsables de cette condition sont tous associés au collagène de type IV dans le corps. Ceux-ci incluent les gènes COL6A1, COL6A2 ou COL6A3.
Cause de la myopathie de Bethlem
La principale cause de la myopathie de Bethlem est la mutation de l’un des gènes du collagène de type IV. Ceux-ci sont appelés COL6A1, COL6A2 et COL6A3. La mutation entraîne la production de protéines anormales de collagène de type IV ou abaisse les niveaux de protéines de collagène IV dans le corps. Comme le collagène est la principale protéine des tissus conjonctifs et qu’il fournit un soutien aux cellules musculaires, la myopathie de Bethlem affecte les muscles du corps.
La raison exacte pour laquelle ces mutations génétiques se produisent dans le corps et conduisent à la maladie n’est pas complètement comprise. Cependant, les cellules musculaires des personnes atteintes de myopathie de Bethlem sont plus sensibles à la mort cellulaire, ce qui entraîne une modification de la mitochondrie, qui est la partie qui fournit l’énergie aux cellules.
Hérédité de la myopathie de Bethlem
Bethlem myopathy is generally an inherited disease. It is known to be ‘autosomal dominant’, meaning that one copy of the mutated gene, inherited from any parent, is enough to give rise to the disease. There is a 50 percent chance that the children of a person suffering from Bethlem myopathy will also inherit the condition. However, some people are diagnosed with Bethlem myopathy and neither of the parents seem to be having it. This means that the parents could be affected so mildly that they never realized that they have the condition. It could also mean that the gene mutation has occurred for the first time in the affected individual.
Symptoms of Bethlem Myopathy
People suffering from Bethlem myopathy experience slowly progressing muscle weakness and also develop joint stiffness in their wrists, elbows, fingers, and ankles. This type of stiffness can restrict movement. The severity of symptoms varies from individual to individual and as with the disease, can appear at any age.
Initial symptoms of Bethlem myopathy can present at any time from birth to adulthood to even in vitro. The symptoms are very variable. For most patients with weakness and contractures, the symptoms of Bethlem myopathy that accompany the disease are known to become worse with age. However, this happens very slowly and varies from person to person. Many adults go through their life being unaware of any muscle weakness or experience only slight contractures. While some need to use equipment to remain mobile such as a cane, wheelchair, or crutches.
Symptoms of Bethlem myopathy during childhood, symptoms can present as hypotonia (floppiness of muscles), joint laxity, delayed motor milestones in a baby, muscle weakness, club foot or taipes, stiffness in the neck known as torticollis, etc. Contractures (tightness) can also occur in the hips, knees, ankles, and elbows. The contractures vary from patient to patient and can also come and go over a period of time. Stiffness of the spine is also known to develop over the years.
If symptoms of Bethlem myopathy present during adulthood then patients can have tight tendons at the back of their ankles along with muscle tightness of other joints such as knees, elbows, and the joints in the back. Muscles in the hands are also particularly affected. Contractures of the finger muscles is a typical symptom of Bethlem myopathy.
Other symptoms of Bethlem myopathy can include:
- Poor stamina
- Low tolerance for exercising
- Difficulty in walking upstairs or doing tasks that require lifting of the arms above the head
- Cachexia
- EMG abnormality
- Abnormality of the cardiovascular system
- Ankle contracture
- Joint stiffness
- Myopathy
Muscles used for breathing are not affected much by this disease and thus, breathing problems are very rare. The heart muscle is also not generally affected.
As collagen type IV is found in the skin, symptoms of Bethlem myopathy are also seen on the skin. The outer surfaces of the arms and legs can feel dry or rough to touch. This is known as keratosis pilaris. Some may discover that they scar in an unusual manner. They may find that the scars either form keloids, which are raised and rather angry looking scars, or they may also have thin, silvery ‘cigarette-like’ paper scars.
Other symptoms of Bethlem myopathy mild weakness in the proximal and extensor muscles can give rise to limited functional impairment. Serum creatine kinase activity has been found to remain normal or slightly elevated. Muscle biopsy has shown non-specific myopathic changes in patients suffering from Bethlem myopathy. In children presenting with Bethlem myopathy, creatine kinase activity has been found to be highly elevated, sometimes even up to 15 times the upper limit of the normal value.
Diagnosis of Bethlem Myopathy
Diagnosis of Bethlem myopathy is generally suspected from medical history and a physical examination. The actual diagnosis is carried out by looking at a particular muscle set or skin through muscle and skin biopsy.
A muscle biopsy involves taking a small piece of muscle, generally from the thigh. Before going ahead with a muscle biopsy, some other tests may also be carried out that help in diagnosis of Bethlem myopathy. These include a blood test that measures the level of the protein creatine kinase (CK). In individuals suffering from Bethlem myopathy, the level of creatine kinase is only slightly elevated.
Muscle ultrasound can also detect changes in the muscle and provide an indication of the overall muscle condition. An ultrasound can provide further evidence of the extent of muscle involvement.
Muscle biopsy is a way of reaching a precise diagnosis. This can be done in the following ways:
Signs and symptoms that may indicate a muscle condition can be observed under a microscope. Muscle fibers of people suffering from muscular dystrophy will not be evenly sized and some of these fibers may also be replaced by fibrous tissue and/or fat.
A biopsy makes it possible to assess the amount of collagen type IV protein that is present in the muscle. This can be seen under the microscope using specific stains to highlight the presence of this protein.
Skin biopsy may also help in the diagnosis of Bethlem myopathy as collagen type IV is usually present in both muscle and skin. In many cases, it becomes easier to detect a reduction of the collagen IV protein by looking at skin cells rather than muscle cells. However, a skin biopsy cannot provide some of the information that a muscle biopsy can and therefore, most doctors prefer to conduct both muscle and skin biopsies to obtain the correct information required for diagnosis.
Genetic tests that look for abnormalities in one of the three genes in which mutation leads to Bethlem myopathy are also available now and can also provide a clear diagnosis.
Other tests that aid in the diagnosis of Bethlem myopathy include:
- Electromyography (EMG)
- Nerve conduction velocity (NCV)
Treatment of Bethlem Myopathy
Il existe un traitement spécifique de la myopathie de Bethlem. Il n’y a que des moyens d’atténuer les effets de la maladie et de prévenir toute autre complication. Des médicaments en fonction de la gravité peuvent être administrés comme traitement de la myopathie de Bethlem.
Si vous allez dans une clinique musculaire, ils vérifieront de près vos articulations et votre mobilité. En collaboration avec votre équipe de physiothérapie, vous pouvez travailler pour étirer les articulations tendues et maintenir la flexibilité et la souplesse de vos muscles. Certaines personnes peuvent également avoir besoin d’une intervention chirurgicale pour libérer le tendon d’Achille. Cela peut aider une personne à se tenir debout et à marcher plus facilement.
Il est conseillé aux enfants et aux adultes souffrant de myopathie de Bethlem de rester actifs et de gérer leur poids dans le cadre du traitement de la myopathie de Bethlem. Le surpoids augmentera encore la pression exercée sur les muscles. Des exercices thérapeutiques, une thérapie physique, une bonne nutrition et un sommeil suffisant peuvent aider à la réparation musculaire, ce qui peut aider à soulager certains symptômes de la myopathie de Bethlem.
