Myotonic dystrophy type 1 (Curschmann-Steinert syndrome) is an autosomal-dominant inherited multisystem disorder with the leading symptoms of muscle weakness and lens opacification (cataract). Two forms of the disease are distinguished: a congenital form, in which the newborn is already conspicuous by muscle weakness (“floppy infant”) and an adult form, which manifests itself only in the 2nd to 3rd decade of life. Myotonic dystrophy type 1 is not curable and, depending on severity and progression, shortens life expectancy.
What is myotonic dystrophy type 1?
Myotonic dystrophy type 1 is one of the so-called trinucleotide repeat disorders. In the genetic code on the long arm of chromosome 19, a trinucleotide is present duplicated from the nucleic bases cytosine, thymine, and guanine. While this base triplet is repeated 5-35 times in healthy individuals, in affected individuals with mild forms of the disease there are about 50-200 repeats, and in severe forms even more than 1000 repeats. The trinucleotide does not directly code for a protein, but influences the synthesis of other proteins. An enzyme required in skeletal and cardiac muscles, dystrophia myotonica protein kinase (DMPK), is produced in reduced amounts as a result of the gene defect. But other proteins are also affected, e.g. SIX5, which is expressed in the lens, or the insulin receptor. Therefore, myotonic dystrophy type 1 affects very many different organ systems. With an incidence of about 1:20000, myotonic dystrophy type 1 is the most common myotonia and also the most common muscular dystrophy occurring in adults. In its inheritance, the number of trinucleotide repeats increases from generation to generation, so that the disease sets in earlier and more severely in the offspring. The congenital form is always inherited from the mother. Boys are more commonly affected by myotonic dystrophy type 1 than girls.
Causes
In the congenital form, the infant is noticeable right after birth for generalized muscle weakness, a raised upper lip, and respiratory insufficiency. Because of the respiratory problems, many newborns are dependent on artificial ventilation and 25%-50% die within the first 18 months of life. Those infants who survive longer are likely to have developmental delays and severe mental retardation. Their life expectancy is approximately 30-40 years. If the disease does not break out until adulthood, affected individuals often first notice muscle weakness in muscles distant from the trunk, especially in the legs and in the neck and facial areas. The facial muscles atrophy, giving patients a gaunt appearance. Speech and swallowing disorders also result. Muscle weakness is accompanied by delayed muscle relaxation, making it difficult for affected individuals to release a handgrip, for example. Other symptoms include lens clouding, sensorineural hearing loss, an increased need for sleep, cognitive impairment, and reduced glucose tolerance and even diabetes mellitus. Due to the disturbed hormone balance, men typically experience testicular atrophy and a bald forehead, and women experience menstrual irregularities. The effects on the heart muscles are particularly dangerous: cardiac arrhythmias frequently occur, occasionally even cardiac arrest. When the muscle weakness reaches the trunk muscles, respiratory disorders and increased susceptibility of the lungs to infection are the result. Myotonic dystrophy type 1 is always progressive, but the severity and composition of its symptoms are highly variable. On average, life expectancy in the adult form of myotonic dystrophy type 1 is approximately 50-60 years.
Symptoms, complaints, and signs
The main feature of myotonic dystrophy type 1 is the delayed slackening of the muscles after a muscle contraction. The disease can be distinguished from other muscular dystrophies by this characteristic. Especially the muscles that are located furthest from the trunk of the body, such as the face, neck, forearm, hand, lower leg and foot muscles, are affected. Independently of the muscle complaints, other symptoms also occur. For example, cardiac arrhythmias or heart failure often occur. Because of cardiac involvement, anesthetic incidents are common during anesthesia. Cataracts and baldness of the forehead in men are often observed. Testosterone levels are too low, which not infrequently leads to testicular atrophy. There is an increased risk of developing diabetes. Speaking and swallowing cause difficulty for patients.Furthermore, the patient is constantly tired during the day, which can lead to nocturnal breathing pauses. However, sleep apnea is not always present. Other symptoms may include digestive disorders, biliousness, or hearing problems. Although it is a hereditary condition, many patients do not experience symptoms until after the age of twenty. Cataracts are 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 developmental disorders.
Diagnosis and course
When myotonic dystrophy type 1 is suspected, molecular genetic methods are used to diagnose the disease without doubt. These help to rule out differential diagnoses with similar symptoms, such as myotonic dystrophy type 2. The diagnosis can be supported by electromyographic (EMG) studies. In affected individuals, typical patterns of spontaneous activity can be found, particularly in the muscles distal to the trunk. A thorough family history is also important, in part to provide further guidance to the family.
Complications
In this disease, affected individuals suffer primarily from severe muscle weakness and discomfort that occurs in the eyes. Cataracts and clouding of the lens occur, so that the vision of the affected person deteriorates significantly. Likewise, in the worst case, complete blindness can occur. The quality of life is significantly reduced. Young people in particular can develop psychological complaints or depression in the event of sudden visual complaints or blindness. Furthermore, heart complaints may also occur, so that the patient may 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 also dependent on the help of other people. Certain activities or sports can no longer be performed without difficulty. 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 the affected person. Usually, no particular complications occur and the patient’s life expectancy is not limited by the disease.
When should one go to the doctor?
The need to see a doctor arises as soon as the affected person experiences impairments in coping with everyday life. Weakness in muscle strength, a decrease in physical performance and shrinkage of tissue are signs of a health disorder. If accustomed sporting activities can only be performed to a limited extent or not at all, the observations should be discussed with a physician. Various investigations must be initiated so that clarification of the cause can be made and a treatment plan drawn up. Delay in voluntary muscle tension and decreased vision are of concern. If blurred vision or clouding of the lens occurs, a visit to the doctor is advised. An irregularity in natural grip function is a warning signal from the body that action is needed. An increased risk of accidents and falls must be discussed with a physician so that countermeasures can be taken. Disturbances of the heart rhythm, palpitations or sleep interruptions should be examined more closely by a physician. If concentration or attention deficits develop, or if reduced mental performance is noticed as a result of the impairments, a visit to the doctor is necessary. If men suffer from reduced sexual desire or develop a bald forehead, a doctor should be consulted. If there are also emotional or mental stresses, the person affected is at risk of developing secondary symptoms. They should be prevented in good time.
Treatment and therapy
Causal treatment of myotonic dystrophy type 1 is not possible. Therapy focuses on symptom relief, such as surgical treatment of the cataract, medication for cardiac arrhythmias, or technical respiratory support.Physiotherapy support can delay the progression of myotonic dystrophy type 1.
Outlook and prognosis
The outlook for a diagnosed myotonic dystrophy type 1 is poor. Both life expectancy and quality of life suffer. Most patients do not even reach the age of 60. Many of them die due to 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 affected individuals show signs of myotonic dystrophy type 1 before the age of 20, while others do not appear at the doctor’s until an advanced age. Within families, there is an increased risk of inheriting the disease. The condition increases continuously because myotonic dystrophy type 1 progresses inexorably over the years. Those affected find it increasingly difficult to cope with everyday life on their own due to the muscle weakness. They are dependent on help. The musculoskeletal system comes to a standstill. After some time, a learned profession can no longer be pursued. The therapeutic approaches of medication and physiotherapy become increasingly ineffective over time. Not infrequently, the physical deterioration of myotonic dystrophy type 1 is accompanied by psychological problems.
Prevention
Because myotonic dystrophy type 1 is an inherited genetic defect, prevention is not possible.
Follow-up care
Myotonic dystrophy type 1 is hereditary. According to the current state of research, a cure is not possible. Life expectancy is reduced by the disease by about 50 years. Follow-up care is advisable to slow down the progression of the dystrophy. Other goals of follow-up care include symptom relief and maintaining quality of life. Follow-up care also involves checking the tolerance of medications, if they have been administered to the patient. Follow-up care is primarily concerned with physical complaints. The mobility of the limbs should be maintained for as long as possible through appropriate exercises. Accompanying psychotherapy may also be appropriate or even necessary. An insufficient quality of life due to the dystrophy can affect the patient mentally. The risk of depression is very high. Psychotherapy offers the possibility to talk about negative feelings. In the advanced stage, a wheelchair is sometimes necessary. During aftercare, the patient learns how to use it on a daily basis. Myotonic dystrophy also affects heart function. A pacemaker counteracts the process. Aftercare is provided by a cardiologist. He monitors the healing process after surgery. Monitoring is discontinued when healing has proceeded as expected.
