Muscular dystrophy - 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 your GP, 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.

Identifying carriers

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.

Prenatal diagnosis

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.