Myotonic dystrophy

Are you suffering from stiffness in your hand muscles after holding some object for a few minutes? If you are, you might be having a genetic disorder known as Myotonic dystrophy (MD). Find out all about the disease and get detailed information about its various symptoms, causes, types, treatment options and life expectancy.

What is Myotonic dystrophy?

It is a form of muscular dystrophy that affects the muscle fibers of an individual, progressively weakening them and making them more susceptible to damage. It is an inherited form of Myotonic muscular dystrophy (MMD).

Myotonic dystrophy Synonyms

The condition is known by various names like:

Picture 1 – Myotonic dystrophy

• Dystrophia myotonica
• Myotonia atrophica
• Steinert’s disease

Myotonic dystrophy ICD 10 Code

The ICD 10 Code for this disorder is G71.1.

Myotonic dystrophy Incidence

The condition is fairly common as around 1 out of every 8,000 people are said to suffer from it. The incidence of the two types of this disorder tends to vary among various ethnic and geographic populations.  Type 1 of this syndrome is believed to be more common than Type 2. According to the findings of some recent studies, however, Type 2 is considered to be as common as Type 1 among inhabitants of Finland and Germany.

The disease may occur in individuals of any age group. However, the symptoms are usually evident in a person when he or she is in 20s or 30s.

Myotonic dystrophy Types

MD is classified into two types, namely:

Type 1 MD (DM1)

It is characterized by weakness in muscles of the face, neck, hands and lower legs. It is also known as Steinert disease and is regarded as the Child Onset Form of MD.

Type 2 MD (DM2)

Its symptoms tend to milder than those of Type 1. It is marked by muscular weakness that primarily affects the shoulders, neck, hips and elbows of sufferers. It is also referred to as Proximal Myotonic Myopathy (PROMM). It is the adult-onset form of MD. It is less common than Type 1.

There is also a variant of Type 1 MD, known as Congenital Myotonic dystrophy. It exhibits itself at birth. The characteristic symptoms of this form of MD include:

• Respiratory problems
• Clubfoot (Foot that turns upwards)
• Delayed development
• Intellectual disability
• Hypotonia or weak muscle tone

Some of the health issues arising from this form of MD can be life-threatening for sufferers.

Myotonic dystrophy Symptoms

MD is primarily characterized by Myotonia, or abnormal stiffness of the muscles, which makes patients unable to relax them voluntarily. The muscles stay contracted for a prolonged duration after use, despite patients trying their best to relax them. A person with MD commonly experiences problems in relaxing the muscles of his/her hand after holding an object, such as a doorknob, for some time. He or she would be unable to relax the grip immediately without some assistance.

The disorder is marked by progressive weakening and wasting of body muscles. The symptoms of MD, it being a progressive disease, generally worsen with increasing age of a patient. The signs and symptoms characteristically make themselves apparent on the face of sufferers and gradually move down towards the shoulder girdle. The face takes on a “hatchet-like” appearance which is characteristic of the disorder. The muscles surrounding the temples begin to appear hollow, due to the involvement of the Temporalis muscle. As the condition progresses, the bottom half of the face and the lower lip sags due to atrophy of the muscles masseter and orbicularis oris.

A notable symptom of MD is the relatively higher strength of the proximal muscles as compared to their distal counterparts all through the duration of the syndrome. However, a number of patients may exhibit weakness in their quadriceps. A patient may have comparatively strong muscles of the leg but may also display a severe weakness of ankle dorsiflexion. This leads to a prominent foot drop.

In the early stages of the condition, patients may suffer from weakness in their neck muscles – particularly the flexors and the sternocleidomastoids. Frontal pattern baldness, along with acute muscular weakening in the lower extremities, is another early sign of MD. In later periods, patients begin to lose the capability of dorsiflexion or movements of the foot. There may also be an involvement of the tongue and the pharynx, which can cause problems like:

• Nasal voice
• Acute problems in swallowing
• Dysarthric speech patterns, marked by difficulty in pronouncing words

The symptoms of the disorder can also be experienced in other parts of the body, mainly in the circulatory system. Cardiac disturbances are commonly noted in MD patients, particularly those suffering from Type DM1. Such cardiac problems mainly manifest through electrical disturbances of the cardiac muscle (Myocardium). Other common heart difficulties include:

• First-degree heart blocks
• Complete heart blocks, which are not as common as first-degrees but can still arise in a sizeable population of MD sufferers.
• Congestive heart failure
• Pulmonary heart disease

During the course of the disease, various systems in the body can be affected. The physical issues that commonly arise due to the condition include:

• Metabolic problems, such as diabetes and insulin resistance
• Gastrointestinal disorders, including lowered GI motility and constipation
• Mental impairment, which results in Hypersomnia and Cognitive dysfunction
• Cataracts
• Testicular atrophy

Men with this condition go through hormonal changes which can make them go bald. Some male sufferers are also found to suffer from infertility and are unable to father a child.

Myotonic dystrophy Causes

The condition is supposed to be hereditary in nature. Both types of the disease are caused by mutations in various genes and are inherited in an autosomal dominant pattern. This indicates that an individual can get this condition if he or she receives only one copy of the mutated gene from either parent. In most cases of MD, patients are found to have only one parent with the disorder.

Since MD is passed on from parents to offspring, it usually manifests earlier in life and its symptoms begin to get more severe. This is known as anticipation and the phenomenon has been reported in case of both types of MD. Anticipation, however, has been reported to be more strongly evident in sufferers of Type 1 of the condition. In this form, a growth in length of the unstable area in the DMPK gene is reported to result in Anticipation. It is not fully clear whether the phenomenon occurs in Type 2 and what it is the mechanism, even if it actually appears.

Myotonic dystrophy and Genetics

Type 1 of the disease (DM1) arises due to mutations occurring in the DMPK gene. Type 2, on the other hand, occurs due to mutations in the CNBP gene. It is unclear what the exact role of these genes is in the human body. According to genetic researchers, the DMPK gene produces a protein that might be responsible for communication within cells. It is supposed to be vital for the proper functioning of cells in the brain, skeletal muscles (which are involved in locomotion) and heart. The CNBP gene manufactures a protein that is mainly found in the skeletal muscles and in the heart. It is believed to have a possible role in assisting regulation of the activities of other genes.

Both forms of MD are supposed to arise due to similar changes in the structure of the genes CNBP and DMPK. There is an unusual repetition of a DNA segment for numerous times in each case, which gives rise to an unstable area in the gene. The mutated gene gives rise to an amplified form of messenger RNA. The messenger RNA is a molecular template of the gene that usually acts as a model for the production of proteins. This unusually long messenger RNA gives rise to clumps within the cell that obstruct the production of numerous other proteins. These changes prevent normal functioning of muscle cells and the cells in other tissues thereby giving rise to the symptoms of MD.

Myotonic dystrophy Diagnosis

The condition is diagnosed with the help of a physical examination. An examination of the physical condition of sufferers can help detect whether the pattern or weakness and wastage of muscles is characteristic of MD. Doctors may also look for other characteristic features of the disease, such as:

• Hatchet-like facial appearance
• Frontal balding
• Difficulty to relax hand muscles after holding objects

A clinical diagnosis of MD can be conducted through laboratory tests like Electromyography (EMG), which involves insertion of a small needle into an affected muscle. The test helps doctors to study the electrical activity of the muscle. EMG test generally shows characteristic firms of electrical discharge in the muscles.

In as many as 50% of MD sufferers, cardiac arrythmias have been diagnosed. Due to this reason, Holtor monitoring is also used as an important diagnostic tool in detecting cases of MD.

The definitive diagnosis of MD is conducted through a genetic test. This examination involves drawing out a sample of blood from patients to detect the mutated gene n the chromosomes that lie inside the WBCs (White Blood Cells).

Myotonic dystrophy Treatment

At present, there is no specific treatment for this disorder. Cure is basically supportive in nature and helps manage the syndrome. Leg braces and ankle supports can prevent worsening of the muscular weakness in patients. In some cases, medicines might also be useful in reducing the intensity of the symptoms of MD in sufferers. Certain drugs can be useful in reducing muscular stiffness. Some symptoms of the disorder, such as eye problems (cataracts) and heart problems, can also be cured.

In some cases, patients suffering from cataract problems may undergo surgery for correction of vision. Physical therapy may be effective in improving muscle strength and tone of sufferers, as well as preserve flexibility in their joints. Certain medications might be useful in easing progressive muscle degeneration and Myotonia.

Myotonic dystrophy Life Expectancy

The lifespan tends to vary from one MD patient to another, depending on the progression of the condition and its symptoms. In some sufferers, the symptoms tend to worsen more quickly than in others. In other cases, patients may survive with the condition for 50-60 years before they begin to suffer from debilitating symptoms.

Myotonic dystrophy Support Groups

MD is a relatively unknown condition and many doctors are unfamiliar with its signs and symptoms. It is due to this reason that the condition might be misdiagnosed. Physicians may also be unable to cure or manage the condition due to their unfamiliarity with MD.  Patients must acquire knowledge about the disease and inform themselves about all the possible dangers that the condition might give rise to. The World Wide Web can be highly assistive in this regard. Patients should also get in touch with organizations dedicated to helping MD sufferers. Some of these support groups include:

Picture 2 – Myotonic dystrophy Image

International Myotonic Dystrophy Organization

P.O. Box 1121

Sunland, CA  91041-1121

Tel: 818-951-2311 866-679-7954

Email: [email protected]

Website: http://www.myotonicdystrophy.org

Centers for Disease Control and Prevention (CDC)

U.S. Department of Health and Human Services

1600 Clifton Road, N.E.

Atlanta, GA   30333

Tel: 800-311-3435 404-639-3311/404-639-3543

Email: [email protected]

Website: http://www.cdc.gov

Parent Project Muscular Dystrophy (PPMD)

401 Hackensack Avenue, 9th Floor

Hackensack, NJ   07601

Tel: 800-714-KIDS (5437)

Fax: 201-944-9987

Email: [email protected]

Website: http://www.parentprojectmd.org

Muscular Dystrophy Association

3300 East Sunrise Drive

Tucson, AZ   85718-3208

Tel: 520-529-2000 800-572-1717

Fax: 520-529-5300

Email: [email protected]

Website: http://www.mda.org

Most of these organizations aid research on the condition and provide support to sufferers of MD. They can provide important information to patients as well as their family members and help them in various other ways.

If you are experiencing the symptoms of Myotonic dystrophy in yourself or observing it in any of your family members, do not delay treatment. Although incurable, the condition can be fairly managed with medical aid and its symptoms can be dealt with. If you suspect yourself to be susceptible to this disorder, go for a predictive testing and find out the approximate age at which you can expect manifestation of the symptoms of MD. This will help you take appropriate steps in delaying the onset of the condition and enjoy a good health as long as possible.

References:

http://www.ncbi.nlm.nih.gov/books/NBK22255/

http://ghr.nlm.nih.gov/condition/myotonic-dystrophy

http://www.genome.gov/25521207

http://www.muscular-dystrophy.org/about_muscular_dystrophy/conditions/103_myotonic_dystrophy

http://medicine.yale.edu/neurology/divisions/neuromuscular/md.aspx