Duchenne's muscular dystrophy is a condition which causes muscle weakness. It starts in childhood and may be noticed when a child has difficulty standing up, climbing or running. It is a genetic condition and can be inherited. It usually affects only boys, although girls may carry the Duchenne gene and symptoms. Those living with Duchenne's muscular dystrophy should have regular check-ups and physiotherapy from childhood, and are likely to need increasing help and treatments from about the age of nine years of age.
What is Duchenne's muscular dystrophy?
Duchenne's muscular dystrophy (DMD) is a genetic
condition which affects the muscles, causing muscle
weakness. It is a serious condition which starts in early
childhood. The muscle weakness is mainly in the
'proximal' muscles, which are those near the trunk of
the body, around the hips and the shoulders. This means
that fine movements, such as those using the hands and
fingers, are less affected than movements like walking.
The muscle weakness is not noticeable at birth, even though
the child is born with the gene which causes it. The weakness
develops gradually. It usually shows up in early childhood.
Symptoms are mild at first, but increase as the child gets older.
The name Duchenne comes from the doctor who first studied
How common is Duchenne's muscular dystrophy?
About 1 in 3,500 children in the UK are born with DMD.
What causes Duchenne muscular dystrophy?
The cause is a genetic change which affects the muscles. Muscles contain a protein called dystrophin, which is necessary for muscles to function properly. People with DMD have a shortage of dystrophin in their muscles. The lack of dystrophin leads to muscle fibre damage and a gradual weakening of the muscles. The shortage of dystrophin is caused by a faulty gene.
How does a faulty gene cause Duchenne muscular dystrophy?
The body is made of cells, and each cell has a 'control centre' which contains genes. The genes are made of DNA. The genes control how the cells make proteins . Every cell contains many different genes and makes many different proteins. One of these proteins is the dystrophin protein which is involved in DMD.
In Duchenne muscular dystrophy, there is a fault in the gene which makes dystrophin. So the muscle cells cannot make dystrophin (or make only a little of it). This leads to muscle damage.
How you get Duchenne muscular dystrophy?
Each person inherits a set of genes is from their father and another set from their mother. The genes have been copied from the parents' cells into the child's cells.
Genes are found on 'chromosomes'. The DMD gene is located on a chromosome called the X chromosome. Boys have one X chromosome and one Y chromosome; girls have two X chromosomes.
DMD is inherited in a pattern called 'X-linked inheritance'. The DMD gene is 'carried' by women, but does not usually cause problems in girls or women (with rare exceptions, below). This is because of there being two X chromosomes in women: one X chromosome has the 'faulty' DMD gene, and the other X chromosome has a normal gene, which compensates for the faulty one.
In contrast, boys with the DMD gene do not have a second X chromosome and so they cannot compensate for the faulty gene. Therefore, boys with the DMD gene always have symptoms of the disease.
The DMD gene can be passed on from parent to child. For a woman who carries the DMD gene, there is a 1 in 2 chance that her sons will have DMD, and a 1 in 2 chance that her daughters will carry the gene.
If my child has DMD, does that mean that other family members have the DMD gene?
Not necessarily. In about half of DMD cases, the fault in the child's gene has not come from the parent. Instead, the fault has arisen while the child's cells were being formed. This can happen if a 'mistake' is made when the parents' genes are copied into the cells which will make the child.
About half the children with DMD will not have family members carrying the gene. DNA testing and specialist genetic advice can help you find out whether the Duchenne gene is carried by other members of the family.
What are the symptoms of Duchenne muscular dystrophy?
- The symptoms usually start around age 1-3 years. Parents may notice:
- Difficulty with walking, running, jumping and climbing stairs. Walking may look different with a 'waddling' type of walk. The child may be late in starting to walk (although many children without DMD also walk late).
- When you pick the child up, you may feel as if he 'slips through your hands', due to looseness of the muscles around the shoulder.
- The calf muscles may look bulky, although they are not strong.
- As he gets older, the child may use their hands to help them get up, looking as if they are 'climbing up their legs'. This is called 'Gower's sign'.
- Some children with DMD also have a learning difficulty. Usually this is not severe.
- Sometimes, a delay in development may be the first sign of DMD. The child's speech development may also be delayed. Therefore, if you have a child whose development is delayed, you may be offered a screening test for DMD. However, DMD is only one of the possible causes of developmental delay - there are many other causes not related to DMD.
What is the outlook for Duchenne's muscular dystrophy?
DMD is a very serious condition and it does shorten life. Because the muscle weakness increases gradually over the years, complications eventually develop. The breathing or heart problems usually become more serious for older teenagers or people in their twenties. In the past, most people with DMD did not live beyond their early twenties. Improvements in treatment have meant that life expectancy has increased. At present, average life expectancy for people with DMD is 27 years. However, there is a lot of individual variation in the severity of DMD and the individual life expectancy.
The most serious complication, and the usual cause of death for people with DMD, is the respiratory complications, such as a severe chest infection at the stage when lung function is already poor.
Can Duchenne's muscular dystrophy affect women who carry the gene?
Girls and women who carry the DMD gene are usually well and have no symptoms of DMD themselves. However, carrying the DMD gene might affect you in one of the following ways:
Passing on the gene
A woman who has the DMD gene can pass it on to her children. Normally there will be a 1 in 2 chance that the gene will be passed on to your child, as explained above. It can be helpful to have advice from a specialist in genetics, who can discuss your individual situation. In many cases, prenatal testing is possible, to find out whether an unborn child carries the DMD gene.
A small number of women carrying the DMD gene may develop
some muscle weakness themselves. This probably occurs in
about 3 in 100 women carrying the gene. The muscle weakness
is usually mild, but there is a lot of individual variation. Rarely,
there can be a muscle weakness similar to boys with DMD.
If there is a weakness, it may progress (increase) slowly over time.
We do not know why some women with the DMD gene get muscle
weakness, while others do not have any symptoms. It may be due
to a process called 'X inactivation', where the 'normal' X chromosome
is not active and therefore cannot compensate for the 'abnormal'
X chromosome which carries the DMD gene.
Some women carrying the DMD gene may develop heart muscle disease (cardiomyopathy) or an abnormal heart rhythm. If this happens, it is usually milder and starts at a later age, compared to boys with DMD. At present, there is a debate about how likely this problem actually is. Recent research from the UK found that most women with the DMD gene had only very minor changes found on heart check-ups. Also, this research found no difference in life expectancy between women carrying the DMD gene and those without it. Other research suggested that 1 in 10 women with the DMD gene might develop some form of cardiomyopathy.
Therefore, some doctors are recommending regular heart check-ups for women who have the DMD gene. For example, they may suggest an ECG and echocardiogram (explained above) once every few years, from around age 20. However, doctors are uncertain as to how much this monitoring is useful or necessary.