Genetic testing and counselling
It may be carried out for a number of reasons, including to:
- diagnose a person with a genetic condition
- help work out the chances of a person developing a particular condition
- determine whether a person is a carrier of a certain genetic mutation that could be inherited by any children they have
You’ll usually need a referral from your GP or a specialist doctor for genetic testing to be carried out. Speak to your doctor about the possibility of testing if you think you may need it.
What does genetic testing involve?
Genetic testing usually involves having a sample of your blood or tissue taken. The sample will contain cells containing your DNA.
It can be tested to find out whether you’re carrying a certain mutation and are at risk of developing a particular genetic condition.
In some cases, genetic testing can be carried out to find out whether a baby is likely to be born with a certain genetic condition.
This is done by testing samples of the fluid that surrounds the foetus in the womb (amniotic fluid) or cells that develop into the placenta (chorionic villi cells), which are extracted from the mother’s womb using a needle.
Depending on the condition(s) being checked for, the fluid or cell samples will be examined and tested in a genetics laboratory to look for a specific gene, a certain mutation on a specific gene, or any mutation on a specific gene.
In some cases, it may be necessary to check an entire gene for mutations using a process called gene sequencing. This has to be done very carefully, and can take a long time compared with most other hospital laboratory tests.
Depending on the specific mutation being tested for, it can take weeks or even months for the results of genetic tests to become available. This is because the laboratory may have to gather information to help them interpret what’s been found.
It isn’t always possible to give definite answers after genetic testing. Sometimes it’s necessary to wait to see if the person being tested, or their relatives, do or don’t develop a condition. Other tests may need to be performed.
You can find out more about genetic testing and how it’s carried out by reading What happens in a genetics laboratory? (PDF, 1.90Mb).
If your doctor thinks genetic testing may be appropriate for you, you’ll usually be referred for genetic counselling as well.
Genetic counselling is a service that provides support, information and advice about genetic conditions.
It’s conducted by healthcare professionals who’ve received training in the science of human genetics (a genetic counsellor or a clinical geneticist).
What happens during genetic counselling will depend on exactly why you’ve been referred.
It may involve:
- learning about a health condition that runs in your family, how it’s inherited, and which family members may be affected
- an assessment of the risk of you and your partner passing an inherited condition on to your child
- a look at the medical history of your family or your partner’s family and drawing up a family tree
- support and advice if you have a child affected by an inherited condition and you want to have another child
- a discussion about genetic tests, which can be arranged if appropriate, including the risks, benefits and limitations of genetic testing
- help understanding the results of genetic tests and what they mean
- information about relevant patient support groups
You’ll be given clear, accurate information so you can decide what’s best for you.
Your appointment will usually take place at your nearest NHS regional genetics centre. The British Society for Genetic Medicine has details for each of the genetics centres in the UK.
Pre-implantation genetic diagnosis
For couples at risk of having a child with a serious genetic condition, pre-implantation genetic diagnosis (PGD) may be an option.
PGD involves using in-vitro fertilisation (IVF), where eggs are removed from a woman’s ovaries before being fertilised with sperm in a laboratory.
After a few days, the resulting embryos can be tested for a particular genetic mutation and a maximum of two unaffected embryos are transferred into the uterus.
PGD has the advantage of avoiding the termination of foetuses affected by serious conditions, but it also has a number of drawbacks.
These include the modest success rate of achieving a pregnancy after IVF, and the substantial financial and emotional costs of the combined IVF and PGD process – PGD isn’t always available on the NHS.