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.

During pregnancy a sample might be taken from the baby.

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

Private testing

Genetics is increasingly becoming a part of everyday medicine. Private clinics now also offer genetic testing with the advantage of shorter referral times and quicker results.

For example Addenbrooke’s Hospital in Cambridge offers private testing in its Genetic Lab:

Genetic counseling

Genetic counseling is a service that provides information and advice about genetic conditions.
Counseling is conducted by healthcare professionals who have been specially trained in the science of human genetics (a genetic counsellor or a clinical geneticist).

Usually you are referred by your GP to your regional genetics service.

There you will probably meet a clinical geneticist who will arrange counseling if necessary.

It helps if you have information about illnesses that run in the family. Do any relatives have genetic disorders, has anyone in your family suffered multiple miscarriages, have there been any early or unexplained deaths?

A counsellor can then help you interpret test results and give you informed advice. Although any decisions are, of course, ultimately yours.

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 counseling can assess the risk of passing the condition on to the child.

Or, if you already have a child with a genetic disorder, they will explain the chances of having another child with the same condition.

Sometimes they might be able to confirm you have a particular gene but not be able to predict how severely your child will be affected.

This section has been adapted from the NHS Choices website.

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