What is genetic testing?
Genetic testing is a means of determining if you are carrying a genetic mutation which has the potential to cause a medical condition. The testing detects changes in the genes, chromosomes and proteins that could result in a genetic condition. It is typically used to assess the risk of developing an inherited disorder and the presence of abnormalities. The test results can be used to determine the chances of an individual developing an inherited disorder and the risk of a parent passing on a disorder to their child.
There are hundreds of different genetic tests being used and new tests are becoming available all the time. Testing usually involves a blood sample being taken and analysed - the sample contains DNA and this is analysed to check for mutations.
Genetic testing is generally only useful if a condition is known to be caused by a specific genetic mutation or abnormality. For example, spinal muscular atrophy is caused by a specific mutation, so it is possible to determine the risk of an individual developing the condition by analysing their DNA.
The testing is done on a voluntary basis and the decision to have a test is down to the individual. There is help and advice available from genetic counsellors to help you decide whether or not to have a test. There are advantages and disadvantages of testing with support and advice available to help you make a decision.
What are the advantages of genetic testing?
Genetic testing can be beneficial regardless of the result. If the result is negative this can provide great relief and peace of mind, while a positive result can enable people to prepare and start making decisions based on information about the condition and advice from doctors and genetic counsellors.
The test result can also give you an idea of your prognosis and enable doctors to be more specific in terms of the information they can give you. The results can also allow treatment planning at an early stage, which can have a positive effect on quality of life and life expectancy.
Test results also have the potential to aid people in making choices about their future, especially in terms of having children. If there is a low risk of passing on a genetic condition, this may give people peace of mind if they are considering having children. While a positive test result may contribute to people deciding not to have children if there is a high risk of their offspring developing the condition.
Screening tests for newborn babies can help to identify conditions at a very early stage, which enables doctors to treat the condition where possible and gives parents time to accept the test result and start preparing for the future.
The major difference between research testing and clinical testing is the purpose of testing: research testing is designed to find out new information about genes and genetics, while clinical testing is intended to learn more about a specific disorder in terms of how it affects an individual or a family unit.
Research testing is important for clinical testing as the more information researchers can find out the better the understanding for doctors and patients. Research testing involves finding new genes, linking genes and genetic mutations to specific medical conditions, and finding out how genes work and affect individuals. The results of research tests are not commonly available for public consumption.
Clinical genetic testing aims to provide patients and families with more information about specific genetic conditions. The results of clinical genetic tests are used to inform people about their condition, so that they are able to make well-informed decisions about their future. Results are also used by doctors to draw-up suitable treatment plans.
It is essential for people to be aware of the difference between research and clinical genetics testing. Patients must consent to both types of testing and the benefits and risks should always be highlighted.
How much does genetic testing cost?
The price of genetic testing varies according to the tests involved and the provider of the test. For example, in the USA the price of testing can be anything from $100 to more than $2000. In the UK certain tests are available on the NHS and therefore free of charge. This includes newborn screening tests, cancer genetic testing and genetic testing for other inherited disorders. DNA tests to determine paternity are not currently available on the NHS and the price varies according to the clinic you choose.
Private testing carries a fee and this will increase if more than one family member is being tested. The cost will depend on a number of factors including the type of test and the clinic you visit. It is always beneficial to get a full written quote beforehand if you do choose a private clinic.
It can take several weeks for the results of the test to become available. Your genetic counsellor or doctor can give you an idea of the expected timeframe and they will be on hand to assist after the results are disclosed.
What is genetic discrimination?
This is a term used to describe when an individual is discriminated against based on the fact that they have a genetic condition or a genetic mutation which increases their danger of developing a specific medical condition. Genetic discrimination can occur in the workplace and some people have suffered this at the hands of insurance providers.
The outcome of genetic testing is usually included in an individual's medical history and will be visible to health insurance companies and potentially employers. This means that it is possible for people who have genetic conditions to experience genetic discrimination. Insurance providers look at medical records when people apply for medical and life insurance, and information about genetic testing may affect the price and type of insurance policy available to the client. Genetic testing is voluntary and people should be aware of the possible implications before they agree to go ahead.
Discrimination of any kind is illegal and if you think you are being discriminated against you should seek advice or talk to your employer.
Does health insurance cover genetic testing costs?
Health insurance policies often cover the cost of genetic testing in instances when it is advised by a doctor. However, this is not always the case and it is best to check with your insurance provider beforehand.
Some people may prefer to cover the cost of genetic testing because the outcome may affect the cost of health insurance.
In the UK many people do not have health insurance because the NHS offers a comprehensive range of treatments and services. If a doctor recommends genetic testing the cost will be covered by the NHS and there are few exceptions.
How is genetic testing done?
It is often recommended by doctors and once an individual has decided to undergo testing the genetic counsellor or doctor will order the tests.
Genetic testing can be carried out on samples of blood, hair, skin or amniotic fluid which surrounds a foetus in the womb. Other types of tissue such as a swab used on the inside of the cheek can also be analysed. The sample will be delivered to a laboratory to be analysed under a microscope by highly trained technician. They look for the presence of specific genes or mutations and will then send a written report detailing the findings to the patient's doctor or geneticist.
Screening tests for newborn babies are done by taking a small sample of the baby's blood. The sample is collected by pricking the heel. If the result is positive further tests will usually be ordered. Unlike most other genetic tests parents are typically only given the result if it is positive.
Doctors and genetic counsellors have a responsibility to explain the testing process and answer any questions a patient has before they begin the process. It is also important to outline the advantages and disadvantages of testing. Patients must consent to testing and it is imperative that they have the relevant information to make an informed decision (informed consent).
What do the results mean?
The results of genetic testing are not simple and it can be complex to interpret and explain them. It is common for patients to have a lot of questions and they must be allowed to discuss the results with their doctor or genetic counsellor. It is vital for doctors and genetic counsellors to take factors such as the individual's medical history and family history into account when they are interpreting the test results.
If the test result is positive this indicates that laboratory technicians detected a change in the chromosomes or genes or found an abnormality or genetic mutation. The test result can be used to rule out or confirm a diagnosis, determine the risk of an individual developing a certain medical condition and determine if the individual is a carrier of a condition, which can imply a risk of passing the disorder onto future generations.
Families have similar genetic information (DNA) and this means that a positive result can have implications for different members of the same family. If you have a relative whom receives a positive genetic test result you may be advised to undergo testing.
It is essential to be aware of genetic testing limitations. In a predictive genetic test it is not usually possible to determine the precise risk of a person developing a medical condition. It is also not usually possible for doctors to use the result of the tests to determine the severity of the condition.
If the test result is negative this means that the technicians did not notice any abnormalities, mutations or changes in the chromosomes and genes. A negative result may indicate that an individual does not have a genetic condition, is not a carrier of a specific condition or they do not have an increased risk. However, a negative result is not always conclusive as it is not possible for tests to identify all genetic changes linked with a specific condition. For this reason additional testing may be necessary.
A negative result may not be useful and this is known as indeterminate, inconclusive, uninformative or ambiguous. Uninformative results may result from polymorphisms (small variations in the DNA) which affect everyone. It can be difficult to decipher a natural polymorphism and a mutation which causes a condition. Inconclusive results cannot rule out or confirm a diagnosis and testing other family members may be useful.
What are the limitations and risks of genetic testing?
Physical risks of genetic testing are minimal, especially for tests that require a blood sample or a swab. Antenatal testing carries a small risk of miscarriage because the test involves taking a sample of the amniotic fluid surrounding the foetus. It is important for parents to be aware of the risks before they agree to have the test.
Additional risks linked to genetic testing include social, financial and emotional risks. The outcome of the test can have far-reaching implications for both the individual and their family members, and it is important that the individual is aware of all the risks associated with genetic testing, as to be prepared for the result.
Genetic testing is useful but it does have limitations. It is not possible for tests to provide all the necessary information about a person's condition; for example, what symptoms they will experience or how severe the condition will be.
Doctors and geneticists will be able to explain the limitations and risks of genetic testing. It is important that people are well-informed before they make a decision on whether or not to undergo genetic testing.
Types of genetic tests
There are many types of genetic tests, including:
- Newborn screening: newborn screening tests are used to diagnose genetic disorders at a very early age. Thousands of newborn babies are tested every year in the UK. Early diagnosis can be beneficial as treatment can then be provided as soon as possible. Babies in the UK are often screened for cystic fibrosis and sickle cell disease.
- Diagnostic testing: diagnostic testing is used to confirm or rule out a diagnosis of a specific medical condition. Tests are usually ordered when a doctor suspects a patient may have a specific disorder. It can be carried out on people of all ages and the results are useful for future planning and drawing up a treatment plan. Diagnostic tests are not possible for all genetic disorders.
- Carrier testing: carrier testing is designed to determine if an individual is a carrier of a specific condition. This means that they have the ability to pass on an inherited disorder without having the condition themselves. Both parents can be tested to determine the risk of passing on a condition if they want to have children. Carriers carry one copy of a mutated gene - for some diseases this is sufficient to pass on a condition, but sometimes two copies of the gene, one from each parent, are needed for a child to develop the condition.
- Prenatal testing: prenatal testing is used to identify genetic changes or abnormalities before a baby is born. Testing may be recommended if there is a higher than normal risk of the baby developing a genetic condition. Prenatal testing is not useful for all disorders but it can help to give parents peace of mind or prepare them for when the baby is born.
- Preimplantation testing: preimplantation testing (sometimes known as preimplantation genetic diagnosis) is a special method used to identify changes in the embryo when fertilisation techniques have been used, such as IVF. The procedure can reduce the danger of the baby developing genetic disorders. It involves taking a small number of cells from the embryo to test for genetic changes before the embryo is implanted.
- Predictive and presymptomatic testing: these tests are used to identify genetic changes when disorders are suspected after birth, or sometimes much later in life. Tests are useful if an individual has a family member with a genetic disorder, as the results may indicate if there is an augmented risk of them developing the same condition. Presymptomatic testing can establish the risk before any symptoms develop. The results can be useful for making decisions about treatment and enable people to gain a better understanding of the condition.
- Forensic testing: forensic DNA testing has made a huge difference to the detection of crimes. It is not employed to identify genetic changes for health purposes, but rather to identify criminals and allow police and investigators to gain a better understanding of what has happened at a crime scene.