Myotonic dystrophy type 1 (Curschmann-Steinert syndrome) is an autosomal dominant inherited multisystem disease with the main symptoms of muscle weakness and clouding of the lens (cataract). A distinction is made between two forms of the disease: an inherited (congenital) form, in which muscle weakness is noticeable even in the newborn (“floppy infant”), and an adult form, which only manifests itself in the 2nd to 3rd decade of life. Myotonic dystrophy type 1 cannot be cured and, depending on its severity and progression, shortens life expectancy.
What is myotonic dystrophy type 1?
Myotonic dystrophy type 1 is one of the so-called trinucleotide repeat diseases. In the genetic code on the long arm of chromosome 19, a trinucleotide from the nucleobases cytosine, thymine and guanine is duplicated. See sciencedict for Introduction to Leprosy.
While this base triplet is repeated 5-35 times in healthy people, affected people with mild disease have about 50-200 repetitions, and with severe forms even more than 1000 repetitions. The trinucleotide does not directly code for a protein, but affects the synthesis of other proteins. An enzyme required in the skeletal and cardiac muscles, the dystrophic myotonic protein kinase (DMPK), is reduced in production due to the gene defect.
But other proteins are also affected, such as SIX5, which is expressed in the lens, or the insulin receptor. Therefore, myotonic dystrophy type 1 affects many different organ systems. With an incidence of approx. 1:20000, myotonic dystrophy type 1 is the most common myotonia and at the same time the most common muscular dystrophy occurring in adulthood.
When it is inherited, the number of trinucleotide repeats increases from generation to generation, leading to earlier and more severe onset of the disease in offspring. The congenital form is always inherited from the mother. Myotonic dystrophy type 1 affects boys more often than girls.
Causes
In the congenital form, the infant is immediately noticeable after birth with generalized muscle weakness, a raised upper lip, and respiratory failure. Because of the breathing problems, many newborns are dependent on mechanical ventilation and 25%-50% die within the first 18 months of life.
Developmental delays and severe mental retardation are to be expected in the longer surviving children. Their life expectancy is around 30-40 years. If the disease only breaks out in adulthood, those affected often first notice muscle weakness in muscles that are far away from the trunk, especially in the legs, neck and face area. The facial muscles atrophy, giving the patient a gaunt appearance.
Speech and swallowing disorders also result. The muscle weakness is accompanied by delayed muscle relaxation, so that those affected find it difficult, for example, to release a handle again. Other symptoms are lens clouding, inner ear hearing loss, an increased need for sleep, cognitive limitations and reduced glucose tolerance up to diabetes mellitus. Due to the disturbed hormone balance, testicular atrophy and a receding forehead typically occur in men and menstrual disorders in women.
The effects on the heart muscles are particularly dangerous: Cardiac arrhythmias often occur, occasionally even cardiac arrest. When the muscle weakness reaches the trunk muscles, breathing disorders and an increased susceptibility to infections of the lungs are the result. Myotonic dystrophy type 1 is always progressive, but the severity and composition of its symptoms are highly variable. On average, the life expectancy for the adult form of myotonic dystrophy type 1 is about 50-60 years.
Symptoms, Ailments & Signs
The main feature of myotonic dystrophy type 1 is the delayed relaxation of the muscles after a muscle contraction. This characteristic can be used to distinguish the disease from other muscular dystrophies. The muscles furthest from the trunk, such as the face, neck, forearm, hand, lower leg and foot muscles, are particularly affected. Apart from the muscle complaints, other symptoms also occur.
Cardiac arrhythmias or cardiac insufficiency often occur. Due to the cardiac involvement, anesthetic incidents often occur during anesthesia. Cataracts and balding in men are often observed. The testosterone level is too low, which often leads to atrophy of the testicles. There is an increased risk of developing diabetes.
Patients have difficulty speaking and swallowing. Furthermore, the patient is constantly tired during the day, which can lead to breathing stops at night. However, sleep apnea is not always present. Other symptoms can include indigestion, bile ailments or hearing disorders. Although it is an inherited condition, many patients do not experience symptoms until after the age of 20.
A cataract is often diagnosed as the first sign of the disease. However, there is also a form of the disease that is present from birth. This congenital form of muscle myotonia is characterized by a particularly severe course with life-threatening respiratory failure and mental and physical development disorders.
Diagnosis & History
If myotonic dystrophy type 1 is suspected, molecular genetic methods are used to unequivocally diagnose the disease. These help to exclude differential diagnoses with similar symptoms, eg myotonic dystrophy type 2. The diagnosis can be supported by electromyographic examinations (EMG). In those affected, typical patterns of spontaneous activity can be found particularly in the trunk muscles. A thorough family anamnesis is also important, also in order to give the family further advice.
Complications
In this disease, those affected suffer primarily from severe muscle weakness and discomfort that occurs in the eyes. This leads to cataracts and clouding of the lens, so that the eyesight of the affected person deteriorates significantly. In the worst case, it can also lead to complete blindness.
The quality of life is significantly reduced. Young people in particular can develop psychological problems or depression if they suddenly have visual problems or go blind. Heart problems can also occur, so that the patient can die of sudden cardiac death. It is not uncommon for those affected to suffer from diabetes.
The muscle weakness significantly restricts the everyday life of those affected, so that in some cases they are dependent on the help of other people. Certain activities or sports can no longer be carried out easily. Children are significantly restricted in their development by the disease, so that complications can arise in adulthood. It is not possible to treat this disease causally.
However, many complaints can be limited and alleviated, so that everyday life becomes bearable for those affected. There are usually no particular complications and the patient’s life expectancy is not limited by the disease.
When should you go to the doctor?
A visit to the doctor is necessary as soon as the person affected experiences impairments in coping with their everyday life. A weakness in muscle strength, a decrease in physical performance and a loss of tissue are signs of a health disorder. If usual sporting activities can only be practiced to a limited extent or not at all, the observations should be discussed with a doctor. Various examinations must be initiated so that the cause can be clarified and a treatment plan can be drawn up.
A delay in voluntary muscle tone and decreased vision are of concern. If your vision becomes blurred or the lens becomes cloudy, you should consult a doctor. An irregularity in the natural gripping function is a warning signal from the body that action needs to be taken. An increased risk of accidents and falls must be discussed with a doctor so that countermeasures can be taken. Heart rhythm disorders, tachycardia or sleep disturbances must be examined more closely by a doctor.
If concentration or attention deficits occur or if reduced mental performance is noticed due to the impairments, a doctor’s visit is necessary. If men suffer from reduced sexual desire or if they develop a receding hairline, a doctor should be consulted. If there are also emotional or mental stress conditions, the affected person is threatened with sequelae. They must be prevented in good time.
Treatment & Therapy
A causal treatment of myotonic dystrophy type 1 is not possible. The therapy focuses on alleviating the symptoms, for example by surgical treatment of the cataract, medication for heart rhythm disturbances or technical respiratory support. Physiotherapeutic support can delay the progression of myotonic dystrophy type 1.
Outlook & Forecast
The prospects for a diagnosed myotonic dystrophy type 1 are poor. Both life expectancy and quality of life suffer. Most patients do not even reach the age of 60. Many of them die from heart failure or succumb to infections. Therapeutic measures can often only marginally alleviate the symptoms of the disease. According to current scientific knowledge, the genetic defect itself cannot be cured. Many of those affected show signs of myotonic dystrophy type 1 before the age of 20. Others only appear to the doctor at an advanced age. Within families there is an increased risk of the disease being inherited.
The suffering continues to increase because myotonic dystrophy type 1 progresses inexorably over the years. Due to the muscle weakness, those affected find it increasingly difficult to cope with their everyday life on their own. You need help. The musculoskeletal system comes to a standstill. After a certain period of time, a learned profession can no longer be pursued. The therapeutic approaches of drugs and physiotherapy increasingly lose their effectiveness over time. It is not uncommon for the physical deterioration of myotonic dystrophy type 1 to be accompanied by psychological problems.
Prevention
Since myotonic dystrophy type 1 is an inherited genetic defect, prevention is not possible.
Aftercare
Myotonic dystrophy type 1 is hereditary. According to the current state of research, a cure is not possible. Life expectancy is reduced by about 50 years as a result of the disease. Follow-up is advisable to slow the progression of the dystrophy. Other goals of follow-up support are symptom relief and maintaining quality of life.
During aftercare, the tolerability of drugs is also checked if they have been administered to the patient. The follow-up care primarily relates to physical complaints. The mobility of the limbs should be maintained for as long as possible through appropriate exercises. Concomitant psychotherapy may also be appropriate or even necessary.
An inadequate quality of life due to the dystrophy can have a psychological impact on the patient. The risk of depression is very high. Psychotherapy offers the opportunity to talk about negative feelings. In the advanced stage, a wheelchair is sometimes required. During aftercare, the patient learns how to use the device on a daily basis.
Myotonic dystrophy also affects cardiac function. A pacemaker counteracts the process. The follow-up treatment is carried out by a cardiologist. He monitors the healing process after the operation. Control ceases when healing is as expected.
