Myotonic Dystrophy

Myotonic dystrophy significantly affects multiple organs and systems involving the skeletal system, cardiac muscles and smooth muscles of the heart. Signs and symptoms of myotonic dystrophy vary with the type of condition that has set in. Some of the common symptoms experienced by the individuals include development of myotonia, characterized by difficulty in releasing grip, abnormal rhythm of heart, weakening of the muscles of upper and lower limbs [6].

Affected individuals also complain of difficulty in swallowing. In addition to these symptoms, individuals also experience cognitive impairment, sleeping difficulties, sleepiness during daytime, development of cataract in early years and infertility [7].

Diagnosis of myotonic dystrophy involves various laboratory studies followed by taking note of family history of the disease and physical examination. The laboratory tests include electrodiagnostic testing, blood tests and muscle biopsy. Of these, muscle biopsy tests hold primary importance to evaluate the reason behind development of muscle weakness. Blood tests would help in identifying the specific gene that is causing the disorder. Various tests to determine heart and lung functioning would also be carried out.

In addition to all the above methods, predictive testing will also be done which can help in identifying the risks of developing myotonic dystrophy much before the signs and symptoms appear [8].

Treatment regime for myotonic dystrophy involves a multidisciplinary approach. This is so because multiple organs and systems are affected by the disorder which indicates a team approach for effective management of the condition. In this, the primary role is that of the neurologist, who would recommend medications such as mexiletine to strengthen the muscles and improve the symptoms. Thereafter, treatment by cardiologists, ophthalmologist and pulmonologist would put in efforts to correct and manage various other symptoms.

Individuals in severe cases would require various mobility aids that include splints and ankle foot orthotics. Those with weakness in neck muscles would be given neck braces. Exercises would also be required to improve the gait of the individuals and the associated symptoms. Aerobic exercises using the stationary bicycle proved to be a safe an effective way for improving the fitness ability in patients with type 1 myotonic dystrophy [9].

Affected individuals who receive proper treatment can live a healthy life. The condition of myotonic dystrophy cannot be treated; however can be effectively managed with appropriate treatment regime to correct all the organs and systems that have been affected. In severe cases, individuals can lead a near to normal life with the help of physical aids and adaptive equipment for improvement in mobility.

The exact cause that triggers the development of myotonic dystrophy is not clearly known. However, genetic factors in an autosomal dominant pattern have been known to cause myotonic dystrophy. The condition is heredity in nature, and therefore individuals with a family history of myotonic dystrophy are likely to develop the same.

The gene involved in development of type 1 myotonic dystrophy is DMPK. Defective gene ZNF 9 on chromosome 3 gives rise to onset of myotonic dystrophy type 2. In this type of genetic defect, there is repetition of 4 nucleotides and such a pattern is termed as tetranucleotide repeat disorder [2].

Myotonic dystrophy type 1 is a much more common disorder than the type 2. The former type has a prevalence rate of 1 per 100,000 population in Japan. The condition has an estimated incidence rate of 3 to 15 per 100,000 in Europe [3]. Type 1 myotonic dystrophy most commonly strikes the pediatric population.

Genetic defect is the major cause of myotonic dystrophy. The repeat in the nucleotide expands and enlarges with each generation, which in turn leads to earlier onset of disease with greater degree of severity.

The gene involved in development of type 1 myotonic dystrophy is DMPK. In this type, there is expansion of triplet repeat of gene cytosine-thymine and guanine. Individuals in whom there are more than 50 expansions exhibit significant signs and symptoms of the disease [4] [5].

The gene that is known to play foul in the causation of myotonic dystrophy type 2 is the ZNF9 on the chromosome 3. In this type, there is repetition of 4 nucleotides and therefore, the expansion is much larger than the type 1 myotonic dystrophy. The size of the expansion of repeated DNA makes no difference on the age of onset for individuals with type 2.

There is no way in preventing the genetic mutations that favor the onset of myotonic dystrophy. However, with the help of predictive testing, it is possible to tell whether an individual is at risk of developing such a type of disorder. It is though not possible to determine the age of onset of the disease. Prenatal diagnosis has provided some useful information regarding whether the fetus is at risk of developing myotonic dystrophy. This testing is carried out at 10 to 12 weeks of gestation through a method known as chorionic villus sampling [10].

Myotonic dystrophy essentially affects various body systems, giving rise to an array of debilitating symptoms. Myotonic dystrophy is of 2 types; namely: myotonic dystrophy type 1 and myotonic dystrophy type 2. The former type is also known as Steinert disease which majorly presents as a congenital disease, but it can affect the adult population too. The second type is a rare occurrence and is also termed as proximal myotonic dystrophy [1].

• Definition: Myotonic dystrophy is a condition characterized by development of myotonia, endocrine changes, defects in the heart conduction and onset of cataracts. It is a chronic type of disorder which gradually progresses and produces debilitating symptoms.
• Cause: Genetic defects are the major cause of myotonic dystrophy. The type of gene involved in type 1 and type 2 myotonic dystrophy include gene DMPK and gene ZNF 9 respectively. Individuals with family history of disorder are at an increased risk of falling prey to it.
• Symptoms: Some of the common symptoms of myotonic dystrophy include weakness in hands and feet, myotonia, cataract, difficulty in swallowing and development of abnormal heart rhythms. In addition, affected individuals also complain of infertility, cognitive difficulties and sleepiness during daytime.
• Diagnosis: Diagnostic procedures include a preliminary thorough physical checkup, followed by several laboratory studies, which involve blood tests, genetic testing, muscle biopsy and electrodiagnostic testing.
• Treatment: Treatment involves a multidisciplinary approach as various organ systems are significantly affected. Primary role is that of neurologist who treats the muscle weakness with help of drug known as mexiletine. 

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