Posted by Dr. Bimal Shah on Friday, 1st March 2013
Introduction
Muscular dystrophy (MD) is a genetic (inherited) condition that gradually causes the muscles to weaken. This leads to an increasing level of disability.
MD is a progressive condition, which means that it gets worse rather than better. It often affects a particular group of muscles, before moving on to other muscles. If MD begins to affect the heart or the muscles used for breathing, it becomes life-threatening.
What causes muscular dystrophy?
MD is caused by mutations (changes) in the genes that are responsible for the structure and functioning of a person�s muscles. These mutations cause changes in the muscle fibres, which interfere with the muscles' ability to function. Over time, this causes increasing disability.
The mutations are often inherited from a person�s parents. If there is a known family history of MD, Dr. B C Shah may be able to refer you for genetic testing and counselling, to give you more information about preventing MD.
Types of muscular dystrophy
There are more than 30 types of MD, each with slightly different symptoms. Not all types of MD cause severe disability.
Some of the more common types of MD are listed below.
Duchenne muscular dystrophy
Duchenne MD is the most common and one of the most severe forms of MD. It usually affects boys and is diagnosed at around three years of age. It starts in the leg muscles before quickly progressing to other muscle groups.
Children with Duchenne MD may be in a wheelchair by 8-12 years old and have a limited life expectancy. While people with Duchenne MD used to be expected to live only into their teens, today most people with Duchenne MD survive well into their 20s and sometimes longer.
Becker muscular dystrophy
Becker MD is closely related to Duchenne MD, but it is milder and less common. Like Duchenne MD, Becker MD tends to affect boys, although it is not usually diagnosed until a child reaches about school age. It also progresses more slowly. Those with Becker MD can walk at least until their late teenage years, and often much longer, sometimes until 40-50 years old or more.
Myotonic muscular dystrophy
Myotonic MD is the most common form of MD in men and women. It can present at any age, even before birth. It can affect many parts of the body, including the muscles, heart and eyes. It is important for this to be diagnosed because of possible problems under anaesthetic and complications for an affected woman in childbirth.
Limb-girdle muscular dystrophy
Limb-girdle MD has around 15 different varieties. It can affect both sexes and usually appears in early adulthood. Limb-girdle MD initially starts in the muscles around the hip and shoulder, but it can also progress quite quickly to other areas.
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral MD affects the muscles in the face (facio), shoulders (scapula) and upper arm (humeral). It can affect both sexes. Symptoms start in childhood or adult life and usually progress slowly.
Oculopharyngeal muscular dystrophy
Oculopharyngeal MD affects the muscles of the eye (ocular) and throat (pharyngeal). The condition affects both sexes, usually starting in middle age.
How common is muscular dystrophy?
. Duchenne MD is the most common type of MD. The second most common type is myotonic MD.
What treatment is available?
Although there is no cure for any of the different types of MD, a range of treatments for MD can help with the physical disabilities and heart problems. These may include:
mobility assistance � including exercise, physiotherapy and physical aids
support groups � to help deal with the practical and emotional impact of MD
surgery � to correct postural deformities such as scoliosis
medication � such as steroid medication to improve muscle strength, or ACE inhibitors and beta-blockers to treat heart problems
Symptoms of muscular dystrophy
The symptoms of muscular dystrophy (MD) and their severity will vary from person to person depending on the type of MD they have.
Typical symptoms of some of the most common types of MD are explained below.
Duchenne muscular dystrophy
Your child will usually start to show signs of Duchenne MD at 1-3 years of age. The muscles around their pelvis and thighs tend to be affected first and often appear bulkier than normal, even though there is progressive weakening. Your child may:
Have difficulty walking
Have difficulty standing up
Be unable to climb the stairs without support
Have behavioural or learning difficulties
Children with Duchenne MD may need a wheelchair by the age of 10. They can also develop scoliosis, in which their spine begins to curve sideways. This can lead to one shoulder or hip being higher than the other.
By the mid-teens, some people with Duchenne MD will develop dilated cardiomyopathy. This is where the condition affects the heart muscles, causing the chambers of the heart to enlarge and the heart walls to become thinner.
By late teens or early twenties Duchenne MD can begin to cause respiratory (breathing) problems. The condition can affect the intercostal muscles (muscle tissue between the ribs) and the diaphragm (the main muscle between the chest and the abdomen that is used during breathing).
Once the heart and respiratory muscles are damaged, Duchenne MD becomes life-threatening. In most cases, someone with Duchenne MD will die from heart or respiratory failure before they are 30 years old.
Becker muscular dystrophy
The symptoms of Becker MD are similar to those of Duchenne muscular dystrophy. However, they are milder and do not usually appear until a person is at least 10 or 11 years old. If your child has Becker MD, they may:
Be late learning to walk
Have muscle cramps when exercising (a painful spasm in the muscle)
Struggle with sport at school
The rate at which someone with Becker MD develops symptoms is very variable. Affected individuals will often first find that they have difficulty running, walking quickly and climbing stairs. As they get older, they may find it difficult to lift objects above waist height. They will often eventually require a wheelchair by 40-50 years old, but this may be much earlier or later.
If you have Becker MD, you are also at risk of developing dilated cardiomyopathy and respiratory problems. However, Becker MD progresses more slowly than Duchenne MD, and those with the condition often have a normal lifespan.
Myotonic muscular dystrophy
As with other types of muscular dystrophy, myotonic MD involves progressive muscle weakness and muscle wasting. However, it is often the smaller muscles, such as those in the face, jaw, neck and hands, and lower legs that are affected first.
As well as muscle weakness and wasting, symptoms can include:
Myotonia (muscle stiffness)
Cataracts (cloudy patches in the lens inside the eye)
Hormonal problems
Excessive sleeping or sleepiness
Behavioural problems in children
Myotonic MD can also cause slow and irregular heart beats (cardiac arrhythmia). Serious problems can develop in about 60-70% of people who have these abnormalities. In some cases, it can cause sudden death.
Myotonic MD can appear at any time between birth and old age. It affects the same number of men and women. The rate of deterioration is often very slow, with little change over a long period of time. Someone with myotonic MD may never have significant disability, although their heart rate will need to be monitored for abnormalities.
Limb-girdle muscular dystrophy
The symptoms of limb-girdle MD often begin during late childhood or early adulthood. There are about 15 varieties that affect both sexes equally.
Limb-girdle MD causes weakness in the big muscle groups in the arms and legs. The first symptoms are often mobility problems affecting the hip girdle. It then progresses to the shoulder girdle (�girdle� means the bones around the shoulder or hip).
If you have limb-girdle MD, you may experience:
Muscle weakness in your hips, thighs and arms
Loss of muscle mass in the affected areas
Back pain
Heart palpitations or irregular heart beats
The muscle weakness will create problems such as:
Difficulty getting out of a low seat
Difficulty lifting objects
Difficulty running
Limb-girdle MD can progress at different rates as it is a group of conditions rather than one single disorder. Some people may be affected in a similar way to boys with Duchenne MD, but more often it has a pattern similar to Becker MD.
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral MD can affect men and women. It tends to affect men slightly more than women, although the reason for this is unclear. The condition usually develops between 10 and 40 years of age, and it progresses slowly.
Symptoms in your child may include:
They sleep with their eyes slightly open
They cannot squeeze their eyes tightly shut
They cannot purse their lips (for example, to blow up balloons)
Teenagers or adults may have aches in their shoulders, rounded shoulders or thin upper arms. As the condition progresses, it usually affects the muscles:
In the face (facio)
In the shoulders (scapula)
In the upper arms (humeral)
In the upper back
In the calves
Around 50% of people with facioscapulohumeral MD develop weakness in their leg muscles. Between 10 and 20% of people will need a wheelchair.
Facioscapulohumeral MD can develop unevenly, so that the muscles on one side of the body may be affected more than the other. Some people may not even be aware that they have the condition until they reach old age. The slow progression means that it does not usually shorten life expectancy.
Oculopharyngeal muscular dystrophy
In oculopharyngeal MD, symptoms are not usually apparent until a person is around 50 or 60 years old, although the abnormal gene that causes the condition will have been present since birth. It affects the muscles in the eyes (ocular) and the throat (pharyngeal).
Symptoms of oculopharyngeal MD can include:
Ptosis (droopy eyelids)
Dysphagia (difficulty swallowing)
Progressive restriction of eye movement as the eye muscles are affected
Limb weakness around the shoulders and hips
As the eyelids droop, they can cover the eyes and impair vision. It is also possible to develop diplopia (double vision).
The dysphagia can eventually make it hard to swallow solid foods and liquids, and even small amounts of saliva. However, with treatment to manage the symptoms, a person�s life expectancy is not usually altered.
Causes of muscular dystrophy
In most cases, muscular dystrophy (MD) is an inherited condition (it runs in families). It is caused by a faulty gene.
Genetics
Genes are units of genetic material (DNA) that determine many of your body's characteristics, such as the colour of your hair and eyes. Each cell in your body contains the same genetic information.
MD is caused by mutations in the genes that are responsible for healthy muscle structure and function. The mutations mean that the cells that should maintain your muscles can no longer fulfil this role, leading to muscle weakness and progressive disability.
Inheriting muscular dystrophy
You inherit your genes from your parents, with one copy of each gene being inherited from each parent (except for conditions, such as Duchenne and Becker MD). If one or both of your parents has a mutated gene that causes MD, it can be passed on to you. MD can be caused by a:
Recessive inherited disorder
Dominant inherited disorder
Sex-linked disorder
These are explained in detail below.
A recessive inherited disorder
If you have a recessive inherited disorder, it means that both of your copies of the gene need to be affected before you would have the condition (a single intact copy of the gene is enough to avoid having the condition). Both the parents and all the children of an affected person are therefore likely to be healthy carriers, with one altered copy of the gene and one intact copy.
Occasionally, an affected person may have an affected child if their partner happens also to be a carrier of the same condition. When a couple are both carriers, there is a 25% (1 in 4) chance of any child being affected.
A dominant inherited disorder
If you have a dominant inherited disorder it means that you will be affected when only one of your two copies of the gene is altered (mutated).
An affected person therefore has a 50% (1 in 2) chance of transmitting this to his or her children.
A sex-linked disorder
A male has an X and a Y chromosome, whereas a female has two X chromosomes. A sex-linked disorder is caused by a mutation in a gene on the X chromosome. As a male has only one copy of each gene on the X chromosome, if one of those genes is mutated then he will be affected.
A woman has two copies of the X chromosome and if she carries one altered copy of a gene then it is less likely to show. If it shows, she will usually be affected less severely than a man.
This explains why sex-linked disorders such as Duchenne MD and Becker MD are more common in men.
Spontaneous gene mutations
Occasionally, spontaneous gene mutations can cause MD. This is where the genes mutate for no apparent reason, changing the way that the cells function. Spontaneous gene mutations can cause MD to develop in people who do not have a family history of the condition.
Another way in which a child may be affected without anyone else in the family being known to have been affected in the past, is when the condition is recessive . The gene mutations may have been in a family for many years but may never have occurred together in the same individual.
Diagnosing muscular dystrophy
Many different methods can be used to diagnose the various types of muscular dystrophy (MD). The age at which MD is diagnosed will vary depending on when symptoms first start to appear.
Diagnosis will usually involve:
Investigating any symptoms
Discussing any family history of MD
Physical examination
Blood tests
A muscle biopsy (when a sample of tissue is removed for testing)
In the first instance, visit Dr. B C Shah if you or your child have any symptoms of MD. If necessary, Dr. B C Shah may refer you to a hospital for further tests.
Investigating symptoms
Dr. B C Shah will need to know about any symptoms of MD that you or your child have noticed, and when they began to appear. For example, you may be:
Finding it hard to climb the stairs
Unable to play sports as you used to
Finding it hard to lift objects
Identifying when symptoms first appeared and determining which muscles are affected are particularly useful in helping to diagnose different types of MD.
Symptoms in young children
Duchenne MD is the most common type of MD in boys. Symptoms can be present from birth but this is unusual and signs usually appear between 18 months and three years old. You may notice that your child has difficulty walking or climbing stairs, or that they fall down more frequently than other children.
Your child might also find it difficult to stand up from sitting on the floor. They may use what is known as the Gower's manoeuvre to do this. The Gower's manoeuvre is where a child stands up by:
Facing the floor
Placing their feet wide apart
Lifting their bottom first
Using their hands to �walk up� their legs (placing their hands first on their knees, then on their thighs)
Visit Dr. B C Shah if you suspect that your child may have MD. He will look at the following when they examine your child.
The way your child stands.
The way your child walks. Children with Duchenne MD often have a typical style of walking, which is sometimes described as �waddling�. Later on, they may tend to stand and walk on the front part of their foot, with their heels off the ground.
Whether your child has an exaggerated inward curve of their lower back. The medical term for this is lordosis. It is also sometimes called �sway back�.
Whether your child has an outward or sideways curvature of their spine, known as scoliosis.
Whether your child�s calves and other leg muscles look large compared with other muscles that may be poorly developed.
Family history
If there is a history of MD in your family it is important to discuss it with Dr. B C Shah. This can help to determine which type of MD you or your child might have.
For example, discussing the family history of limb-girdle MD will help Dr. B C Shah to determine if your type of MD is a recessive or a dominant inherited disorder.
Blood tests
A sample of blood may be taken from a vein in your or your child's arm to test it for creatine kinase, a protein usually found in muscle fibres. When muscle fibres are damaged, creatine kinase is released into the blood. The muscle damage caused by MD means that the level of creatine kinase in the blood will be higher than normal.
Muscle biopsy
A muscle biopsy is when a small sample of muscle tissue is taken so it can be examined under a microscope and tested for proteins. The sample will usually be taken from the leg or arm, depending on the type of MD.
Analysing the protein in the muscle can help to determine which gene is causing the MD, and therefore which type of MD you have. For example, people with Duchenne MD and Becker MD have an abnormal amount of the protein dystrophin in their muscles and it is usually an altered size.
Examining the muscle tissue under a microscope can help diagnose limb-girdle MD. Healthy muscle consists of closely packed, evenly-sized fibres. In people with limb-girdle MD, these fibres may be missing, of different sizes or replaced with fat.
Other tests
A number of other tests can be used to find out more about the spread and extent of any muscle damage. This will help your doctor to identify or confirm which type of MD you have. Treatment can then be directed where it is most needed. Some tests are explained below.
A magnetic resonance imaging (MRI) scan uses a strong magnetic field and radio waves to produce detailed pictures of the inside of your body. This can help to identify the affected muscles, and will also show the extent of any muscle damage.
A computerised tomography (CT) scaninvolves taking a series of X-rays to create a detailed image of the inside of your body. This will reveal any muscle damage.
A chest X-ray can be useful for looking for breathing or heart symptoms. It will show up any abnormal enlargement of the heart, plus any fluid in or around the lungs.
In an electromyography (EMG) test a needle is inserted into the muscle to measure the electrical activity of the muscles when they are resting and when they contract (shorten). By measuring the muscle�s response, it is possible to see the extent of muscle damage.
In an electrocardiogram (ECG) electrodes (flat metal discs) are attached to the arms, legs and chest to measure the electrical activity of the heart. This is used to check for an irregular heartbeat and reveal any damage.
An echocardiogram is an ultrasound scan of the heart using sound waves. It gives a clear picture of the heart muscles and valves so the heart structure and function can be checked.
Treating muscular dystrophy
At present there is no cure for muscular dystrophy (MD), but a variety of treatments can help to manage the condition.
As different types of MD can cause quite specific problems, the treatment that you receive will be tailored to your needs. As your symptoms develop, Dr. B C Shah who is treating you should advise you about the options.
New research is investigating possible future treatments. Improved genetic testing can help if you are concerned about passing the condition on to your children.
Mobility assistance
As MD progresses it weakens your muscles and you gradually begin to lose mobility and strength. These physical problems can be helped with the following:
Exercise keeps the muscles working in a good condition, because a lack of activity can make the condition worse
Physiotherapy can be useful for maintaining muscle strength and also the length of tendons, which is important for preserving flexibility and preventing stiff joints
Physical aids, such as a wheelchair, leg braces or crutches, can help you to maintain standing and stay mobile
Support groups
Muscular dystrophy can affect you emotionally as well as physically. Support groups and organisations may help you to understand and come to terms with your condition better. They can also provide useful advice and support for those who care for people with MD.
Steroid medication
In people with Duchenne MD, corticosteroid medication has been shown to improve muscle strength and function for six months to two years. For some people, it can improve:
The time it takes to stand up from the floor
Walking speed
The ability to climb stairs
The ability to lift weights
Some side effects, such as weight gain and excessive hair growth, are associated with using steroid medication.
Surgery
In some severe cases of MD, surgery may be necessary to correct postural deformities. For example, if you or your child has Duchenne MD, you (or they) may develop scoliosis, which is where the spine curves to the side.
Surgery can correct the scoliosis, although there have been no trials to evaluate its effectiveness. Surgery is aimed at:
Halting the progression of MD
Improving cosmetic appearance
Maintaining movement and function in the upper limbs and chest
Increasing life expectancy
If you or your child may benefit from having surgery you will be referred to Dr. B C Shah to discuss the procedure and the risks involved.
Other kinds of surgery may be used to treat specific symptoms. For example, if you have ptosis (droopy eyelids) caused by oculopharyngeal MD, surgery can successfully lift the eyelids away from your eyes and restore your vision. Several treatments are also available for dysphagia(difficulty swallowing).
Treating heart complications
Some types of MD can affect the heart muscles and the muscles used for breathing. When the condition has progressed to this stage it can become life-threatening.
It is important that your heart function is assessed regularly once MD has been diagnosed. For Duchenne and Becker MD, a magnetic resonance imaging (MRI) scan or an echocardiogram (ECG) should be carried out about once a year to check for any damage.
If any damage to your heart is detected you may be referred to a cardiologist (a heart specialist) for tests every three months. You may also be prescribed medication to treat your heart problems. ACE inhibitors relax your arteries, making it easier for your heart to pump blood around your body. Beta-blockers can control irregular heart beats (arrythmias) and make it easier for your heart to work.
In some cases of myotonic MD, a pacemaker may be fitted to correct an irregular heartbeat. A pacemaker is a small, battery-operated device that can be implanted into your chest to regulate your heartbeat.
New research
New ideas for MD treatments are currently being developed. Dr. B C Shah treating you may also know of any recent developments that might benefit you.
Speak to Dr. B C Shah if you are interested in taking part in a clinical trial (a form of research that tests one treatment against another).
Some examples of current research ideas are explained below.
Stem cell research
Stem cells are cells that are at an early stage of development. This means they have the ability to turn into any type of cell in the body. Some research is currently focusing on whether stem cells can be turned into muscle cells and used to regenerate damaged muscle tissue.
Exon skipping
In the future, �exon skipping� may be a way of treating Duchenne MD. Exons are sections of genetic coding (DNA) that contain information for proteins. In Duchenne and Becker MD, some of the exons are missing or duplicated, which can interfere with the dystrophin protein being produced.
Researchers are currently investigating ways of �skipping� additional exons in the dystrophin gene. This could mean that more dystrophin would be produced, reducing the severity of MD symptoms.
The trials at the moment are focused on treatment that would apply to Duchenne MD but it may become applicable to Becker MD in the future.
Genetic testing for muscular dystrophy
Genetic testing may be useful for prospective parents who have a family history of MD and are worried about passing the condition on.
Speak to Dr. B C Shah, who can refer you for genetic screening and counselling.
Genetic testing
Genetic testing can be used to:
Identify carriers of the condition
Perform a prenatal diagnosis (where a foetus is tested during pregnancy)
Identifying carriers
Some types of MD are carried without causing clear signs of the condition. This applies to recessive inherited disorders, sex-linked conditions and even some dominant conditions (particularly myotonic dystrophy). Genetic testing can determine who is carrying the disorder.
For example, a woman with a family history of Duchenne MD but no symptoms herself may be carrying the gene that causes it. DNA can be taken from cells in the blood, saliva or tissue. The DNA in the relevant gene can then be tested to find out if she is carrying the faulty gene.
If you or your partner are a carrier of MD and are at risk of passing the condition on to your child, your genetic counsellor will discuss your options with you.
Prenatal diagnosis
Genetic testing can be used for prenatal diagnosis. This is when a baby is diagnosed with MD before it is born, using tests that are carried out during pregnancy. If you are pregnant and there is a possibility that your unborn baby has MD, you may be offered tests.
There are two main ways of performing these tests. One is chorionic villus sampling (CVS). This is when tissue from the placenta is removed for analysis early. This is often at less than 11 weeks into the pregnancy.
The other method is amniocentesis, which is not usually carried out until 15-16 weeks. In amniocentesis a needle is inserted into your abdomen to take a sample of amniotic fluid (the fluid that surrounds the foetus in the womb). This fluid contains cells that have been shed by the foetus. Both tests carry a risk of causing miscarriage.
The cells from the foetus can be tested to determine whether they have the genetic mutation that is responsible for MD. If they do, the baby is likely to develop MD at some stage after birth. If this is the case your genetic counsellor will be able to discuss your options with you.
Be aware that there are limitations to this kind of diagnosis. Tests can give misleading results or unexpected, unanticipated results. It is important to discuss prenatal testing and the meaning of the possible results before going ahead with the procedure.
A normal test result does not ensure that the baby will be healthy. The test only looks for the particular type of MD in the family but not for all other possible problems. Prenatal diagnosis can only be performed if there is a precise genetic diagnosis of the family�s condition.
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