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.
Read more about genetics.
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 (see above). The gene mutations may have been in a family for many years but may never have occurred together in the same individual.
The Muscular Dystrophy Campaign has more information on the specific causes of different types of muscular dystrophy.
