What are muscular dystrophies?
The muscular dystrophies (MD) are a group of inherited genetic conditions that gradually cause the muscles to weaken. This leads to an increasing level of disability.
MD is a progressive condition, which means that it gets worse over time. It often begins by affecting a particular group of muscles before affecting the muscles more widely.
Some types of MD eventually affect the heart or the muscles used for breathing, at which point the condition becomes life threatening.
There is no cure for MD, but treatment can help manage many of the symptoms.
Why it happens
MD is caused by changes (mutations) in the genes responsible for the structure and functioning of a person's muscles.
These mutations cause changes in the muscle fibres that 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, your doctor may be able to refer you for genetic testing and counselling to evaluate the risk that you might develop the condition or have a child with MD, and to discuss the options available to you.
Types of muscular dystrophy
There are many different types of MD, each with somewhat different symptoms. Not all types of MD cause severe disability and many do not affect life expectancy.
Some of the more common types of MD include:
- Duchenne muscular dystrophy – one of the most common and severe forms, it usually affects boys in early childhood; men with the condition will usually only live into their 20s or 30s
- myotonic dystrophy – a type of MD that can develop at any age; life expectancy is not always affected, but people with a severe form of it may have shortened lives
- facioscapulohumeral muscular dystrophy – a type of MD that can develop in childhood or adulthood, it progresses slowly and is not usually life threatening
- Becker muscular dystrophy – closely related to Duchenne MD, but it develops later in childhood and is less severe; life expectancy is not usually affected so much
- limb-girdle muscular dystrophy – a group of conditions that usually develop in late childhood or early adulthood; some variants can progress quickly and be life threatening, whereas others only develop slowly
- oculopharyngeal muscular dystrophy – a type of MD that usually doesn't develop until a person is 50-60 years old and doesn't tend to affect life expectancy
- Emery-Dreifuss muscular dystrophy – a type of MD that develops in childhood or early adulthood; most people with this condition will live until at least middle age
Who is affected?
More than 70,000 children and adults in the UK have MD or a related condition.
Duchenne MD is the most common type of MD and affects around one boy in every 3,500 in the UK. The second most common type is myotonic MD, which affects around one person in every 8,000.
Facioscapulohumeral MD is believed to affect around 1 in every 20,000 people in the UK, which would make it the third most common type.
Treating muscular dystrophy
Although there is no cure for MD, a range of treatments can help with the physical disabilities and problems that may develop. These can 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 steroids to improve muscle strength, or ACE inhibitors and beta-blockers to treat heart problems
New research is looking into ways of repairing the genetic mutations and damaged muscles associated with the condition. There are currently promising clinical trials for Duchenne MD. Search for [clinical trials for muscular dystrophy].
Read more about treating MD.
Muscular dystrophy symptoms
There are many different types of muscular dystrophy (MD). All cause muscle weakness, but the areas affected and the severity of the symptoms are different.
Typical symptoms of some of the most common types of MD are explained below. The Muscular Dystrophy Campaign also provides a list of specific neuromuscular conditions.
Duchenne muscular dystrophy
Because of the way it's inherited (see causes of muscular dystrophy), Duchenne MD mostly affects boys. Girls can occasionally be affected, but the condition tends to be milder in females.
Children with Duchenne MD usually start to have noticeable symptoms between the ages of one and three years. The muscles around their pelvis and thighs tend to be affected first and often appear bulkier than normal.
A child with Duchenne MD may:
- have difficulty walking, running or jumping
- have difficulty standing up
- learn to speak later than usual
- be unable to climb the stairs without support
- have behavioural or learning difficulties
Children with Duchenne MD may need a wheelchair by the time they are 8-14 years old, as their muscles weaken and they lose the ability to walk. They can also develop scoliosis, which is where the 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 their late teens or early 20s, people with Duchenne MD can begin to have breathing problems. The condition can affect the intercostal muscles (muscle tissue between the ribs) and the diaphragm (main muscle between the chest and abdomen used during breathing).
Once the heart and respiratory muscles are damaged, Duchenne MD becomes life threatening. With medical care, most people with Duchenne MD die from heart or respiratory failure before or during their 30s.
As with other types of muscular dystrophy, myotonic dystrophy involves progressive muscle weakness and muscle wasting. However, it is often the smaller muscles that are affected first, such as those in the face, jaw and neck.
Myotonic dystrophy can appear at any time between birth and old age. It affects the same number of men and women.
As well as muscle weakness and wasting, symptoms can include:
- muscle stiffness (myotonia)
- clouding of the lens in the eye (cataracts)
- excessive sleeping or sleepiness
- swallowing difficulties (dysphagia)
- behavioural and learning problems in children
- a slow and irregular heartbeat (cardiac arrhythmia)
Myotonic dystrophy is very variable and sometimes gets worse only very slowly, with little change over long periods of time. However, it can become more severe as it is passed down through the generations in a family.
Some people with myotonic dystrophy may never have a significant disability, although their heart rate will need to be monitored for abnormalities. This is because there is a risk of a serious problem where the electrical impulses that control the heartbeat travel too slowly through the heart. In some people, the condition can also cause cataracts to develop at a younger age than usual.
Life expectancy for people with myotonic dystrophy can vary considerably. Many people have a normal life expectancy, but people with the more severe congenital form of the condition (present from birth) may die while still a newborn baby or only survive for a few years.
Some people who first develop symptoms as a child or teenager may also have a shortened life expectancy.
Most deaths related to myotonic dystrophy are related to pneumonia, breathing problems or heart problems.
It is important for someone with myotonic dystrophy to know about their condition and to tell any doctor they see that they are affected, as it can lead to difficulties with general anaesthetics and childbirth.
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral MD can affect both men and women. It tends to affect men slightly more than women, although the reason for this is unclear. Men also tend to be affected earlier and more severely.
About one in three people with facioscapulohumeral MD are unaware of any symptoms until well into adulthood, but others develop problems in early childhood. The condition tends to progress slowly.
Symptoms in your child may include:
- sleeping 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 shoulder aches, rounded shoulders or thin upper arms. As the condition progresses, it usually affects the muscles in the:
- face (facio)
- shoulders (scapula)
- upper arms (humeral)
- upper back
Around half of all people with facioscapulohumeral MD develop weakness in their leg muscles and 1 or 2 in every 10 people with the condition will eventually need a wheelchair.
Facioscapulohumeral MD can develop unevenly, so the muscles on one side of the body may be affected more than the other.
As the condition progresses slowly, it does not usually shorten life expectancy.
Becker muscular dystrophy
Like Duchenne MD, Becker MD mostly affects boys. Becker MD also affects similar areas of the body to Duchenne MD, although the symptoms tend to be less severe.
Symptoms of Becker MD usually begin in childhood, but they are often relatively mild at this point. For example, a child with the condition may:
- learn to walk later than usual
- have [muscle cramps] when exercising
- struggle with sport at school
During late childhood or early adulthood, 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 the time they are 40-50 years old, but this is variable. For example, one person with Becker MD may become unable to walk at 16 years, while another person may walk until they are 80.
If you have Becker MD, you are also at risk of developing dilated cardiomyopathy and breathing problems. However, Becker MD progresses more slowly than Duchenne MD, and those with the condition often have a normal lifespan.
Limb-girdle muscular dystrophy
Limb-girdle MD is the name given to a number of related conditions that cause weakness in the big muscle groups at the base of the arms and legs (around the shoulders and hips).
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).
Symptoms of limb-girdle MD usually begin in late childhood or early adulthood, although the condition can affect people younger or older than this, depending on the specific type. The condition affects both sexes equally.
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 heartbeats
The muscle weakness will create problems such as difficulty lifting objects, running or getting out of a low seat.
How quickly limb-girdle MD progresses depends on the specific type. Many types get worse slowly, but others can develop more rapidly.
Oculopharyngeal muscular dystrophy
In oculopharyngeal MD, symptoms are not usually apparent until a person is around 50 or 60 years old. 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 become 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 double vision (diplopia).
The dysphagia can eventually make it hard to swallow solid foods, liquids and even small amounts of saliva. This can lead to chest infections if food and drink is accidentally swallowed the "wrong way" into the lungs. However, with treatment to manage the symptoms, a person's life expectancy is not usually altered.
Emery-Dreifuss muscular dystrophy
People with Emery-Dreifuss MD usually begin to develop symptoms during childhood or adolescence.
In the early stages, people with the condition usually develop muscle contractures. This is where muscles and tendons become shortened and tightened, limiting the range of movement at nearby joints.
Areas commonly affected by muscle contractures include the arms, neck and feet. This means that people with Emery-Dreifuss MD may have difficulty straightening their elbows or bending their neck forward, for example.
Like all types of MD, Emery-Dreifuss MD also causes progressive muscle weakness, usually beginning in the shoulders, upper arms and lower legs. This can make it hard to lift heavy objects or raise your arms above your head, and you may have an increased tendency to trip over things.
Later on, the hip and thigh muscles become weaker. This can make activities such as walking up stairs difficult. People with Emery-Dreifuss MD will often eventually require a wheelchair as they become unable to walk.
Emery-Dreifuss MD can also affect the electrical signals to the heart, causing heart block. This can cause people with the condition to develop an abnormally slow heartbeat and palpitations, which can lead to episodes of lightheadedness or fainting. The slow heartbeat can often be treated successfully with an implanted pacemaker.
Because of the risk of serious heart and respiratory problems, someone with Emery-Dreifuss MD will often have a shortened life expectancy. However, most people with the condition live until at least middle age.
Muscular dystrophy causes
In most cases, muscular dystrophy (MD) runs in families. Usually, you develop it after inheriting a faulty gene from one or both of your parents.
MD is caused by mutations (alterations) in the genes 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 (see box, right). If one or both of your parents has a mutated gene that causes MD, it can be passed on to you.
Depending on the specific type of MD, the condition can be a:
- recessive inherited disorder
- dominant inherited disorder
- sex-linked (X-linked) disorder
In a few cases, the genetic change (mutation) causing MD can also develop as a new event in the family. This is known as a spontaneous mutation.
These are explained in more detail below.
A recessive inherited disorder
If you have a recessive inherited disorder, it means you have inherited an altered version of the gene that causes the condition from both of your parents (both your copies of the gene are altered).
If a child only inherits an altered version of the gene from one parent, they will become a carrier of the condition. This means they are not affected, but there is a chance any children they have will be if their partner is also a carrier.
If both parents carry an altered version of the gene that causes the condition, there is a:
- one in four chance their child will have MD
- one in two chance their child will be a carrier
- one in four chance their child will be healthy (not inherit any mutated genes)
Some types of limb-girdle MD are inherited in this way.
A dominant inherited disorder
A dominant inherited disorder means you only need to inherit the mutated gene from one parent to be affected.
This means that if you have a child with an unaffected partner, there is still a 50% chance of your child developing the condition.
Types of MD inherited in this way include myotonic dystrophy, facioscapulohumeral MD, oculopharyngeal MD and some types of limb-girdle MD.
A sex-linked (X-linked) disorder
Chromosomes are long, threadlike structures that contain DNA and are found in each of the body's cells. Most chromosomes are the same in males and females, except for the pair of sex chromosomes, the X and Y chromosomes. A male has one X and one 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 males only have one copy of each gene on the X chromosome, they will be affected if one of those genes is mutated.
As females have two copies of the X chromosome, they are less likely to develop an X-linked condition because the normal copy of the chromosome can usually compensate for the altered version.
Females can still be affected by X-linked disorders, but the condition is usually less severe than when the gene alteration is present in an affected male.
Types of MD inherited this way include Duchenne MD and Becker MD, which is why these conditions are more common and more severe in males.
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 a child with no family history can be affected is when the condition is recessive. The gene mutations may have been present on both sides of the family for many generations, but may not have affected anyone until a child inherited a copy of the altered gene from both parents.
Muscular dystrophy diagnosis
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 involve some or all of these stages:
- investigating any symptoms
- discussing any family history of MD
- physical examination
- blood tests
- electrical tests on the nerves and muscles
- a muscle biopsy (when a sample of tissue is removed for testing)
In the first instance, visit your doctor if you or your child have any symptoms of MD. If necessary, your doctor may refer you to a hospital for further tests.
Your doctor 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 is 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 12 months and three years of age. 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 by placing their hands first on their knees, then on their thighs
Visit your doctor if you suspect that your child may have MD. Your doctor 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, although it is also sometimes called "sway back"
- whether your child has a sideways curvature of their spine, known as scoliosis
- whether your child's calves and other leg muscles look large compared with other muscles
If there is a history of MD in your family, it is important to discuss it with your doctor. This can help determine which type of MD you or your child might have.
For example, discussing the family history of limb-girdle MD will help your doctor determine if your type of MD is inherited as a recessive or a dominant condition (see causes of muscular dystrophy for more information).
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 some types of MD means that the level of creatine kinase in the blood will often be higher than normal.
A blood sample may also be used for genetic testing, and this can sometimes identify the cause of muscle problems without the need for a muscle biopsy.
A muscle biopsy is when a small sample of muscle tissue is removed through a small cut (incision) or a hollow needle 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 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 too little of the protein dystrophin in their muscles and it is usually an altered size.
Examining the muscle tissue under a microscope can also 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, different sizes, or have been replaced with fat.
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.
- nerve conduction studies and electromyography (EMG) – tests used to examine the electrical activity in nerves and muscles at rest and when the muscles are contracting; this can help decide whether the underlying problem is in the spinal cord, in the muscles themselves, or in the nerves carrying impulses between the spinal cord and the muscles
- magnetic resonance imaging (MRI) scan – a test that uses a strong magnetic field and radio waves to produce detailed pictures of the inside of your body; this can help identify the affected muscles and will also show the extent of any muscle damage
- computerised tomography (CT) scan – where a series of X-rays are taken to create a detailed image of the inside of your body; this will reveal any muscle damage.
- chest X-ray – this can be useful for looking for breathing or heart symptoms, as it will show up any abnormal enlargement of the heart, plus any fluid in or around the lungs
- electrocardiogram (ECG) – where 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
- echocardiogram – 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
Treatment for muscular dystrophy
There is currently no cure for muscular dystrophy (MD), but a variety of treatments can help manage the condition.
As different types of MD can cause quite specific problems, the treatment you receive will be tailored to your needs. As your symptoms develop, the healthcare professionals 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.
Read more about genetic testing.
Mobility and breathing 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:
- low-impact exercise, such as swimming
- physiotherapy can be useful for maintaining muscle strength, preserving flexibility and preventing stiff joints
- physical aids, such as a wheelchair, leg braces or crutches, can help you maintain standing and stay mobile
Once the chest muscles become too weak to control breathing properly, you may require machines to assist with your breathing and coughing, especially while sleeping.
In people with Duchenne MD, corticosteroid (steroid) medication has been shown to improve muscle strength and function for six months to two years and slow down the process of muscle weakening.
Steroid medication for Duchenne MD is available in tablet or liquid form, and current research suggests a daily dose is most effective. However, long-term use of steroids is associated with significant side effects, such as weight gain and excessive hair growth.
Recent research has also shown that a creatine supplement can help improve muscle strength in some people with MD while causing few side effects.
Creatine is a substance normally found in the body that helps supply energy to muscle and nerve cells. It is often available as a supplement from pharmacies and health food stores.
If you have MD and decide to take creatine supplements, make sure you mention this to your doctors (doctor and specialist).
Treating swallowing problems
People with some types of MD find it increasingly difficult to swallow (dysphagia) as the condition progresses. This can increase your risk of choking or developing a chest infection if food and liquids get into the lungs.
Depending on the severity of your swallowing problems, there are a number of treatments that can be used.
For example, a dietitian may help you alter the consistency of your food and you may be taught some exercises by a speech and language therapist to help improve the function of your swallowing.
If necessary, surgery can also be used to treat swallowing problems. This may involve a minor procedure to cut one of the muscles in your throat, or a small balloon may be inflated in your gullet (oesophagus) to expand it.
If MD progresses to a point where you are unable to get enough nutrition by swallowing, a feeding tube (gastrostomy or PEG) may need to be surgically implanted into your stomach through your belly (abdomen).
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, an electrocardiogram (ECG) examination of heart rhythm will be carried out at regular intervals, and an echocardiogram may also be performed from time to time. A magnetic resonance imaging (MRI) scan may sometimes also be used to check for problems with the heart.
If any damage to your heart is detected, you may be referred to a cardiologist (a heart specialist) for further tests and possibly more frequent monitoring.
You may also be prescribed medication to treat your heart problems, such as ACE inhibitors to relax your arteries and make it easier for your heart to pump blood around your body, or beta-blockers to control irregular heartbeats (arrhythmias or dysrhythmias).
In some cases of myotonic or Emery-Dreifuss 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.
In some severe cases of MD, surgery may be necessary to correct physical problems that can occur as a result of the condition.
For example, if your child has Duchenne MD, there is a chance they will develop scoliosis (where the spine starts to curve sideways). Surgery can correct the scoliosis or prevent it getting worse, although there have been no trials to evaluate its effectiveness.
Other kinds of surgery may be used to treat specific symptoms, such as:
- droopy eyelids (ptosis) can be lifted away from the eyes to improve vision
- tight joints caused by tendon contractures can be loosened to improve movement by lengthening or releasing the tendons
- weak shoulder muscles may be improved by surgically fixing the shoulder blades to the back of the ribs (scapular fixation) – however, there have been no trials to evaluate the effectiveness of this treatment
If you or your child may benefit from having surgery, you will be referred to a specialist to discuss the procedure and the risks involved.
Research into treatments
New ideas for MD treatments are currently being developed.
Speak to your doctor or specialist if you are interested in [taking part in a clinical trial].
Your doctor or the healthcare professional treating you may know of any recent developments in healthcare that may benefit you.
Some examples of current research ideas are explained below.
Trials are now in progress in the UK and Netherlands to see if "exon skipping" may be a useful 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.
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.
Muscular dystrophy prevention
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 your doctor, who can refer you for genetic screening and counselling.
Genetic testing can be used to:
- identify the cause of muscle problems (to make a diagnosis)
- identify carriers of the condition (people who don't have the condition, but have the potential to pass MD on to their children)
- determine a prenatal diagnosis (where a foetus is tested during pregnancy)
Genetic testing is likely to be used more often in the future, as knowing the precise cause of the MD may make a difference to what type of treatment will be most effective.
Some types of MD can be carried without causing clear signs of the condition. This applies to recessive inherited disorders, sex-linked conditions and even some dominant conditions. Genetic testing can determine who is carrying the disorder.
Read more about the causes of muscular dystrophy for more information about how MD is inherited.
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 her blood, saliva or tissue and compared with a sample from a family member who has the condition 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.
Genetic testing can also be used for prenatal diagnosis. This is when a baby is diagnosed with MD before it is born using tests carried out during pregnancy. If you are pregnant and there is a possibility that your unborn baby has MD, you may be offered these tests.
There are two main ways of performing prenatal diagnosis. One is chorionic villus sampling (CVS). This is when tissue from the placenta is removed for analysis, usually after no less than 11 weeks into the pregnancy.
The other method is amniocentesis, which is not usually carried out until 15-16 weeks of pregnancy. In amniocentesis, a needle is inserted into your belly (abdomen) to take a sample of the amniotic fluid that surrounds the foetus in the womb. This fluid contains cells that have been shed by the foetus. Both of these tests carry a small risk of causing miscarriage.
The cells from the foetus can be tested to determine whether they have the genetic mutation 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, which will often include terminating the pregnancy. Such decisions can be very difficult and very personal, and different people have very different feelings about what to do.
Be aware that there are limitations to this kind of diagnosis. Tests can give misleading or unexpected results. It is important to discuss prenatal testing and the meaning of the possible results before going ahead with the procedure. Expert genetic counselling can be very helpful in these circumstances to help people make the decision that is right for them.
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.
Newer tests are being developed that can be performed by taking a sample of blood from the mother and testing the free foetal DNA (ffDNA). This is known as non-invasive prenatal diagnosis (NIPD).
At present it is used to determine the sex of a foetus when it is medically important to know this, as well as the foetus' Rhesus blood group. It is hoped it will soon be able to diagnose conditions such as Duchenne MD.
Pre-implantation genetic diagnosis (PGD)
For couples at risk of having a child affected by MD, another possible option is to use in vitro fertilisation (IVF) and then test early embryos for MD. This allows doctors to only transfer unaffected embryos into the woman. This is known as pre-implantation genetic diagnosis (PGD).
While PGD has the advantage of avoiding the termination of foetuses affected by the condition, it also has a number of drawbacks. These include the modest success rate of achieving a pregnancy after IVF, as well as the substantial social, financial and emotional burdens of the combined IVF and PGD process. Apart from couples who need IVF so they can conceive a child, the number of people who use PGD is small.
Read more about IVF.