Genetics - Genetic testing and counselling 

Genetics services 

Genetic testing can be used to find out whether a person is carrying a specific genetic mutation (altered gene) that causes a particular medical condition.

Read more about genetic inheritance and genetic mutations.

Genetic testing

Genetic testing usually involves having a sample of your blood or tissue taken. The sample will contain cells that contain your DNA and can be tested to find out whether you are carrying a particular mutation and are at risk of developing a particular genetic condition.

Genetic testing is only useful if it is known that a specific genetic mutation causes a condition. For example, a specific gene is known to cause spinal muscular atrophy (a condition where there is muscle weakness and progressive loss of movement). It is therefore possible to test a blood sample 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 a few particular mutations, which means it is relatively easy to test for.

However, Marfan syndrome (a condition that affects the body's connective tissues) can be caused by any one of hundreds of different possible mutations in a particular gene. 

Gene sequencing

For a condition such as Marfan syndrome, a scientist in a laboratory will have to check the entire gene for mutations, using a process called gene sequencing. This has to be done very carefully, and it can take a long time compared to most other hospital laboratory tests. 

For example, the Marfan syndrome gene contains more than 200,000 letters of DNA code, divided into 65 parts. And, this is not even the largest human gene.

Even when a mutation is found, much work may still be needed to determine whether or not it is actually the cause of the condition.

NHS genetics services

There are 32 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 trained in genetics and skilled at providing advice about genetic conditions. Many conditions can be caused by more than one gene and can be inherited in different ways. 

Determining the cause and pattern of inheritance is important. This is because it makes it easier to advise someone about their choices 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, including:

  • obstetricians (specialists in the care of women during pregnancy) they may send a sample of fluid from the womb of a pregnant woman for chromosome tests
  • paediatricians (specialists in conditions that affect children) and neurologists (nervous system specialists) they often seek advice about diagnosis and genetic tests
  • oncologists (specialists in cancer) and surgeons   they may refer people or their families for genetic tests if they are at increased risk of getting cancer

Genetics is increasingly becoming a part of everyday medicine. 

Genetic counselling

Genetic counselling is a service that provides information and advice about genetic conditions.

Counselling is conducted by healthcare professionals who have been specially trained in the science of human genetics (a genetic counsellor or a clinical geneticist).

The counsellor will discuss the risks, benefits and limitations of genetic testing with you. They will also explain how 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 is usually very important. Identifying family members who have had the condition in the past will help determine which genetic tests may be appropriate.

Geneticists will be able to explain the results of any tests or examinations that you have and help you decide how to progress.

A geneticist can also help assess 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 them with you. They can help you decide whether to have cancer screening or other tests.


Page last reviewed: 30/07/2012

Next review due: 30/07/2014

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What happens in a genetics laboratory?

Find out more about genetic testing and how it is carried out by reading 'What happens in a genetics laboratory?' (PDF, 1.90Mb).