Genetic testing
Genetic testing is a way of finding out whether you are carrying a particular genetic mutation (altered gene) that causes a medical condition. See Genetics - genetic inheritance for more information about genetic mutations.
Genetic testing usually involves having a sample of your blood or tissue taken. The sample will contain cells that contain your DNA. The sample can then be tested to determine whether you are carrying a particular mutation and are at risk of a particular genetic condition.
Genetic testing is only effective if it is known that a specific genetic mutation causes a condition. For example, it is known that a specific gene causes spinal muscular atrophy (a condition that causes muscle weakness and a progressive loss of movement). It is therefore possible to test a sample of blood for the presence or absence of this gene.
Some genetic conditions are caused by particular mutations. Others can be caused by any mutation in a gene. For example, cystic fibrosis is usually caused by only a few particular mutations, so it is relatively easy to test for it in the laboratory. However, Marfan syndrome (a condition that affects the body's connective tissues) can be caused by any one of hundreds of different mutations in a particular gene.
Gene sequencing
For a condition such as Marfan syndrome, the laboratory has to check all the way through the gene for mutations, using a process called gene sequencing. This has to be done extremely carefully, and can take a long time compared to most other hospital laboratory tests.
The Marfan’s gene, for example, contains more than 200,000 letters of DNA code, divided into 65 parts. This is not even the largest human gene.
Even when a mutation is found, it may be necessary to do a lot of work to determine if that mutation is actually the cause of the condition or not. If, as often happens, a mutation is not found, the diagnosis may have to be reconsidered. There are at least two genes that can cause conditions similar to Marfan’s syndrome if they have mutations within them.
NHS genetics services
There are 27 NHS genetics centres in the UK. These are organised on a regional basis and include both clinical and laboratory services, which work closely together.
Clinical geneticists are doctors who are trained in genetics and skilled at advising on genetic conditions. Many conditions can be caused by more than one gene and can be inherited in a different ways. It is important to determine the cause and pattern of inheritance, as it is easier to advise on the choices that may be available if a firm diagnosis has been made.
GPs and hospital doctors may make referrals to genetics services, often at the request of people with a genetic condition or their families.
Many other specialists also use NHS genetics services:
- obstetricians (specialists in the care of women during pregnancy) refer samples of fluid from the womb of a pregnant women for chromosome tests
- paediatricians (specialists in conditions affecting children) and neurologists (specialists in the nervous system) often seek advice on diagnosis and genetic tests
- oncologists (specialists in cancer) and surgeons may refer people or their families for genetic tests if they are more likely to get cancer
Genetics is increasingly becoming a part of everyday medicine.
Genetic counselling
Genetic counselling is another term for advice given by healthcare professionals about genetic conditions. It may take the form of a discussion with a healthcare professional who is trained in the science of human genetics (a geneticist). This professional may be:
- a genetic counsellor
- a clinical geneticist (a doctor who specialises in genetics)
- a specialist, such as a paediatrician (a doctor who specialises in childhood health)
The healthcare professional will discuss the risks, benefits and limitations of genetic counselling with you. They will also explain that the information found as a result of genetic testing could have implications for both you and your family.
Genetics services often help people with genetic conditions who want to have children. For example, if someone has an inherited condition and wants to become a parent, genetic counselling can assess the risk of passing the condition on to the child.
Your family history will usually be very important. Seeing who may have had the condition in the past will help indicate what genetic tests may be appropriate (see above). Geneticists can explain the results of any tests or examinations and help you decide how to progress.
Alternatively, a geneticist may be involved in assessing your risk of developing a particular condition. For example, if you have a strong family history of cancer, a geneticist will assess your risks and discuss this with you. They can help you to decide whether you would like to have cancer screening or other further tests.
