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Understanding Muscular Dystrophy

What is Muscular Dystrophy?

The term muscular dystrophy refers to a group of genetic diseases marked by progressive weakness and degeneration of the skeletal, or voluntary, muscles, which control movement. The muscles of the heart and some other involuntary muscles are also affected in some forms of muscular dystrophy, and a few forms involve other organs as well. We know that many muscle-wasting diseases are caused by defects in genes for muscle proteins.

Does Muscular Dystrophy Affect Children Exclusively?

No. Muscular dystrophy can affect people of all ages. While some forms first become apparent in infancy or childhood, others may not appear until middle age or later. With improved medical care, particularly of problems affecting the heart and lungs, children with muscular dystrophy are living further into adulthood than ever before.

What are the Forms of Muscular Dystrophy?

The major forms of muscular dystrophy are myotonic, Duchenne, Becker, limb-girdle, facioscapulohumeral congenital, oculopharyngeal, distal and Emery-Dreifuss.

How do the Forms of Muscular Dystrophy Differ?

They differ in severity, age of onset, muscles first and most often affected, the rate at which symptoms progress, and the way the disorders are inherited.

What Causes Muscular Dystrophy?

Flaws in muscle protein genes cause muscular dystrophies. Each cell in our bodies contains tens of thousands of genes. Each gene is a string of the chemical DNA and is the "code" for a protein (another way to think of a gene is that it’s the "instructions" or "recipe" for a protein). If the recipe for a protein is wrong, the protein is made wrong, in the wrong amount or sometimes not at all.

Are Muscular Dystrophies Always Inherited?

Muscular dystrophies are generally inherited but in some cases no family history exists. The most common and most severe form of muscular dystrophy, affecting 1 per 3500 live male births. Inherited in a sex-linked, recessive manner, affecting boys.

Is Muscular Dystrophy Contagious?

No. Genetic diseases aren’t contagious.

Can Something Be Done About the Symptoms of Muscular Dystrophy?

Yes. Moderate exercise programs and physical therapy minimize contractures, a condition often associated with muscular dystrophy in which shortened muscles around joints cause abnormal and sometimes painful positioning of the joints. In addition, certain exercises may prevent or delay scoliosis, or curvature of the spine. Rehabilitative devices, ranging from canes to powered wheelchairs, help maintain mobility and independence as long as possible. Surgical procedures can sometimes be helpful in relieving muscle shortening caused by some forms of muscular dystrophy. Special kinds of respiratory care, especially when the dystrophy has progressed for several years, are also important. Deep breathing and coughing, sometimes with the aid of special devices, is often recommended.

Medications know as corticosteroids have been found to slow muscle destruction in Duchenne muscular dystrophy. However, these potent anti-inflammatory drugs have serious side effects, such as weight gain, bone loss, cataracts, skin problems, high blood pressure, susceptibility to infection, and psychological difficulties. Researchers are testing a new corticosteroid that may have fewer side effects. They’re also studying how these drugs slow muscle destruction with the aim of obtaining this effect with a less toxic medication.

How are the Muscular Dystrophies Inherited?

All genes are inherited, half coming from a child’s mother, the other half from the father. Flaws in genes can be inherited along with the parents’ genes, although they can also occur for the first time in a child. Scientists use the term ‘spontaneous mutation’ when this happens. Doctors use the term ‘familial’ for a disease that occurs with a family history and ‘sporadic’ when there’s no family history. Sporadic diseases can nevertheless stem from gene flaws.
 

Duchenne Muscular Dystrophy

Onset:  early childhood – about 2 to 6 years

Symptoms:  generalized weakness and muscle wasting affecting limb and trunk muscles first. Calves often enlarged.

Progression:  disease progresses slowly but will affect all voluntary muscles. Survival rare beyond mid twenties.

Inheritance:  X-linked recessive (females are carriers)


The Natural Course of the Disease

Although the disease is present from conception, symptoms do not usually develop until the child is 5 or 6 years old, or perhaps even a year or two later. The symptoms result form weakness of the muscles. First, a boy affected with Duchenne muscular dystrophy will have some difficulty in keeping up with other children when running. He’ll develop a characteristic "waddling" run (as he becomes weaker) that will also be present when he walks. He’ll have difficulty going up steps, and have to first put one foot, then the other foot, on the same step before moving on to the next one. Soon he’ll have to pull himself up using the handrail. Over the next few months, he will walk more and more on his tiptoes, and develop a forward curvature of his spine – a "lordosis". At this stage, his muscles will look healthy or may even be enlarged – "’pseudohypertrophy". He’ll start to fall more often and be able to rise again only by pulling on objects or by placing his hands on the floor while standing and then lifting his upper body by "climbing" up on his legs with his hands. He’ll soon have to get of a chair in the same way. Inevitably, the weakness progresses until the child can no longer walk and requires the use of a wheelchair. The age at which this happens varies, but most children are between 8 and 10 years old and virtually all use a wheelchair by age 12. Although weakness of the arms is present early, it does not advance as rapidly as in the legs, and causes no real problems until after the boy begins using a wheelchair. The child experiences progressive loss of strength in the shoulders and upper arms until it becomes impossible to life objects of any weight, and eventually impossible to list his hands to his mouth. Strength in the fingers and hands is retained, but it, too, eventually decreases and fine movements become limited and clumsy.

As the amount of time a child with Duchenne dystrophy uses a wheelchair increases, he develops more curvature of the spine, but now to the side – "scoliosis" – as well as to the back. Eventually, his body curves until his ribs may be resting on his hip bones. The affected youngster may also develop tightening of the joints or "contractures" at the hips, knees, ankles, shoulders and elbows, to the point where the legs are bent up against the stomach with the feet pointing down and the arms locked into the sides with elbows bent. With additional weakness of the chest muscles, the youngster will be unable to breathe deeply or cough properly, and even minor colds and chest infections have a high chance of leading to pneumonia. Severe respiratory problems mark the disease’s final stages, usually claiming the lives of those affected during their twenties. The heart muscle is affected at times, and some children may die of heart failure.

Medical Intervention / Therapy

There is still no treatment at this time that has proven to be effective in stopping the degeneration of muscle in Duchenne dystrophy. Medical therapy is aimed at slowing some complications in the disease.
Regular physical therapy from an early stage may help to delay the development of contractures at the joints, but, to be effective, this must be carried out daily. Wearing braces or splints on the legs, particularly at night, may also help slow the development of the contractures. The combination of braces and a walker will often allow the child to be independently mobile for a longer period. Walking, however, will still be slow and difficult and he’ll have to use a wheelchair for gradually increasing periods.

Some children are treated with corticosteroid medications, usually prednisone, which may help to preserve strength and may allow them to walk a little longer. Unfortunately, since this medication has serious side effects, it’s not universally used. Side effects include marked weight gain, acne, weakening of bones, increased likelihood of infections, and a greater chance of developing diabetes and cataracts.

The increased time a boy with Duchenne dystrophy spends walking and even standing in braces will help to prevent scoliosis. However, nine out of ten affected children will eventually develop severe scoliosis if nothing is done to prevent it. For this reason, the child will often undergo an operation in his early teens in which a steel rod will be placed along the spine to prevent progressive curvature. In addition to these measures, various types of environmental adaptations need to be made to help the child remain independent in daily activities. These adaptations may include raised toilet seats, special shower chairs, special desk tops, ramps instead of steps and handrails.

All respiratory infections must be treated vigorously, and should be prevented. These children should receive yearly vaccinations against pneumonia and influenza. They should be kept out of school during cold or influenza epidemics and should be taken to the physician if they develop symptoms. Affected children will still develop marked disability even if all known therapeutic measures are followed, but they will experience much less physical and emotional discomfort as a result of scoliosis or muscle contractures, remain mobile longer, and their lives may be prolonged for several years.
 

Becker Muscular Dystrophy

Onset:  Adolescence or adulthood
Symptoms:  Almost identical to Duchenne but often much less severe. Can be significant heart involvements
Progression:  Slower and more variable than Duchenne with survival well into mid to late adulthood
Inheritance:  X-linked recessive (females are carriers)

Emery-Dreifuss Muscular Dystrophy (EDMD)

Onset:  Childhood to early teens
Symptoms:  Weakness and wasting of shoulder, upper arm and shin muscles. Joint deformities are common
Progression:  Disease usually progresses slowly. Frequent cardiac complications are common.
Inheritance:  X-linked recessive (females are carriers)

Limb-Girdle Muscular Dystrophy (LGMD)

Onset:  Late childhood to middle age
Symptoms:  Weakness and wasting affecting shoulder and pelvic girdles first
Progression:  Usually progresses slowly with cardiopulmonary complications often occurring in later stages of the disease
Inheritance:  Autosomal recessive, X-linked recessive


Facioscapulohumeral Muscular Dystrophy (FSH or FSHD)

Onset:  Childhood to early adulthood
Symptoms:  Facial muscle weakness, with weakness and wasting of the shoulders and upper arms
Progression:  Progresses slowly with some periods of rapid deterioration. Disease may span many decades
Inheritance:  Autosomal dominant

Myotonic Dystrophy (DM)

Onset:  Childhood to middle age
Symptoms:  Generalized weakness and muscle wasting affecting face, feet, hands and neck first. Delayed relaxation of muscles after contraction. Congenital myotonic form is more severe
Progression:  Progression is slow, sometimes spanning 50 to 60 years
Inheritance:  Autosomal dominant

Oculopharyngeal Muscular Dystrophy (OPMD)

Onset:  Early adulthood to middle age
Symptoms:  First affects muscles of eyelid and throat
Progression:  Slow progression with swallowing problems common as disease progresses
Inheritance:  Autosomal dominant

Distal Muscular Dystrophy (DD)

Onset:  40-60 years
Symptoms:  Weakness and wasting of muscles of the hands, forearms and lower legs
Progression:  Slow progression but not life-threatening
Inheritance:  Autosomal dominant

Congenital Muscular Dystrophy (CMD)

Onset:  At birth
Symptoms:  Generalized muscle weakness with possible joint deformities
Progression:  Disease progresses very slowly. Fukuyama form is more severe and involves mental functions
Inheritance:  Autosomal recessive, autosomal dominant

Resources

Learning and Working with Disabilities – Information Resource Guide
Toronto Board of Education – Employment Equity Office, Ph: (416) 393-0760
The Muscular Dystrophy Association of Canada
357 Bay St. 10th Floor, Toronto Ontario M5H 2T7
Neuro-Muscular Clinic, Bloorview-MacMillan Center
350 Runsey Rd., Toronto, Ontario

Websites:

www.mdausa.org
http://muscle.ca/

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