Steinert’s disease is a rare disease that mainly affects the muscles. Of genetic and hereditary origin, it leads to progressive muscle weakness. What are the symptoms of this disease? How is it diagnosed? What is the treatment?
Definition: what is Steinert’s disease?
Also called “myotonic dystrophy type 1” or DM1, Steinert’s disease is a neuromuscular, genetic and hereditary disease. It is estimated to affect one person in 10,000, i.e. approximately 8,000 in France. It affects both women and men and can occur at any age. “Very disabling in the long term, this condition is called “multi-systemic” because it affects both the muscles (weakening and atrophy of the muscles, called “dystrophy”, lack of muscle relaxation called “myotonia”), but also other organs ( cardiorespiratory system, digestive system, nervous system, hormonal system, etc.), explains Gérard Rivière, President of the Association of Friends of the Steinert Disease Information Portal. It is expressed and evolves very differently from one patient to another and the genetic anomaly has no treatment yet. On the other hand, some of his symptoms can be taken care of”.
What are the symptoms of Steinert’s disease?
The disease is mainly characterized by muscular symptoms such as:
- Muscle stiffness
- Significant and increasing fatigue
- A decrease in muscle volume
- Difficulty walking, to speak, to hold his head, to lift and hold a heavy object.
But the disease can also affect other organs than the muscles, such as:
► The heartwhich leads to heart rhythm disturbances
► The respiratory system, causing difficulty breathing with coughing and shortness of breath, even sleep apnea, resulting in poor blood oxygenation and excess carbon dioxide.
► The central nervous systemwith neurological disorders (hypersomnolence: tendency to fall asleep easily, to sleep for a long time), even cognitive disorders
► The hormonal system, the patients then present a malfunction of the sexual glands leading to a decrease in fertility
► The eyeswith the early development of a cataract.
The symptoms can be very different from one person to another, depending in particular on the age of onset, which has led to the classification of the disease into several “forms“.”They range from the most serious form, called “neonatal”, when symptoms are apparent from birth, at so-called “late or asymptomatic” forms, when symptoms occur late or are very mild and inconspicuous“, specifies Gérard Rivière.
What is the cause of Steinert’s disease?
“This disease is said to be “autosomal dominant”, that is to say that it suffices that one of the two parents is affected (both the mother and the father) so that the risk of transmission to children exists. This risk is one in two (50%) at each birthwhich means that in a sibling descended from a carrier parent, all the children may be affected, or only a few or none.“, explains Gérard Rivière. It is due to a abnormality in the DNA of a gene located on chromosome 19. This gene codes for an enzyme (DMPK, for Dystrophy Myotonin Protein Kinase) which is involved in particular in the functioning of the muscles. “The defect, a sort of “bug”, consists of a abnormal repetition of a sequence of 3 “letters” in the DNA of the gene, explains our expert.
There is no transmission of the disease other than genetic
This repetition, which ranges from 50 to several thousand times, disrupts not only the production of DMPK, but also the synthesis of other proteins necessary for the proper functioning of all the organs of the body. The number of these repetitions is generally correlated with the severity of the symptoms and the earliness of their onset.“. This tends to increase from generation to generation, if the disease is passed on.”This last point explains the frequent worsening of the disease during genetic transmission from one generation to the next“, notes Gérard Rivière. The cause of the initial DNA mutation in the first affected parent in a pedigree is not known. There is no transmission of the disease other than genetic (no contagion between individuals). To know. “If one of the parents knows that he is a carrier of the disease, possibilities exist to avoid transmitting the disease future children through prenatal diagnosis or preimplantation diagnosis, both of which are legally permitted in the case of this disease“, notes Gérard Rivière. This approach is unfortunately not possible if the carrier parent is unaware that he is affected (young, asymptomatic), with the risk of having a child carrying a more serious form, as mentioned above.
The disease is suspected in the presence of suggestive symptoms and/or the existence of attacks in the family history. But it will only really be confirmed after genetic analysis, thanks to a simple blood test. A electromyogram (a test that measures the electrical activity of the muscle) can sometimes be done.
Unfortunately, there is currently no treatment that can cure the genetic origin of this disease (we must be able to intervene on the DNA or RNA in the nucleus of all cells in the body) . The treatments therefore consist of multidisciplinary symptom management : to slow stiffness and muscle weakness, physiotherapy sessions are generally prescribed; on the cardiac level, the patient often not having particular symptoms, a regular monitoring is set up (electrocardiogram, pose of holter, etc.), and, according to the evolution, the installation of a pacemaker may be necessary for preventive purposes, to avoid dangerous cardiac dysfunctions (risk of sudden death); on the respiratory level, the measurement of oxygen and carbon dioxide in the blood is regularly measured and, if necessary, a nocturnal breathing aid can be put in place (NIV, non-invasive ventilation); daytime sleepiness can be controlled with medication; when it interferes with vision, the cataract is operated on; psychological support can also be provided to patients. with the realization of electrocardiogram and the installation of a Holter. Occasionally, the installation of a pacemaker can be proposed, for preventive purposes, in order to prevent excessive cardiac slowing down; on the respiratory level, the measurement of oxygen and carbon dioxide in the blood is regularly measured; drowsiness can be controlled with medication; when it interferes with vision, the cataract is operated. psychological support can also be given to patients. “Treatments to globally correct the genetic anomaly are being studied, in particular by genetic therapy. Encouraging results have already been obtained and preliminary clinical trials are underway in different countries“, reveals our expert.
What is the life expectancy with Steinert’s disease?
Apart from the severe forms of the newborn, life expectancy is almost normal if symptoms are well managed, including cardiac monitoring.
Thanks to Gérard Rivière, President of the Association of Friends of the Steinert Disease Information Portal.
To know more :
– Rare Diseases Info Services: 0 810 63 19 20 Azur number
– AFMTELETHON French Association against Myopathies
– Association Friends of the Information Portal on Steinert’s Disease