Predictive testing

A predictive test can provide information about whether or not someone will develop or is likely to develop a specific condition, often later in life.

The test is usually performed on a blood sample. The blood is analysed in a genetics laboratory to test if a person has inherited a faulty gene associated with a condition.

Taking a genetic test is your choice and you should never feel pressured into taking it by health professionals, family or friends. It is also a long process which can involve several sessions with the genetic health professional, and months waiting for the results from the laboratory.

You may be given information that is very new to you and quite complicated, and it can be difficult to take it all in. It’s a good idea to take a support person, such as a friend or partner, with you to your appointments. You may want to ask them to take notes during the appointments. It is important that you have the opportunity to discuss genetic testing with a trained genetic health professional. They will be able to provide you with all the information you need in order to make the decision that is right for you. They will also be able to help you discuss any emotional issues that may arise, and answer any questions or concerns you may have.

Remember that there is no going back after you receive your test results. There is no way to ‘unknow’ your result. It is important therefore to try and think through some of the main issues before making a decision. Some of these are discussed below and might give you some useful questions to think about and discuss. The list however, is not complete, and not all the points will be relevant to your specific situation.

If there is a known genetic condition in your family, and the faulty gene that causes that condition is known, then you might be able to have a predictive test to see if you have inherited the faulty gene. You might want to have a test if:

  1. the condition can be prevented or its symptoms effectively treated or managed, or if
  2. the condition can neither be prevented, nor its symptoms effectively treated, but:
  • you want the information to help with decisions about having children, or to tell you more about your own children’s risks.
  • you believe that knowing more about your chance of getting the disease will help you to make important life decisions including decisions about your health care.
  • you are the type of person that prefers to know more about your own future and prefers to live with certainty than with uncertainty.

Predictive test results carry a degree of uncertainty, even if very slight. In most cases (apart from cancer), having a faulty gene usually shows that you will go on to develop the condition being tested for. However, it will still be difficult to predict when the condition will develop, how severe it will be, or how rapidly the symptoms will progress.

Remember that in scientific terms a positive test result means you DO carry the genetic change and a negative test result means that you DO NOT carry the genetic change. Most often the results will be one or the other.

However, there is sometimes a third possibility: a grey zone or ‘intermediate’ test result. This means that even though a change in the gene is found, it is difficult to know whether in this case it will cause the condition. This is usually rare, but can be a very frustrating result to receive.

You should discuss all these possible outcomes with a genetic specialist when you are deciding whether to take the test.

Before you can proceed with predictive testing, it must be confirmed that you are at risk. First, a detailed family history will be done to see if you are at risk of having the genetic condition. 

In most cases, if genetic testing is possible, a close relative of yours who is affected by the condition will be offered genetic testing first in order to identify the genetic change that runs in the family. If a specific genetic change is found in their blood sample then it is possible to take a blood sample from you to see if you have also inherited the same genetic change. 

If the result of this test shows that you have inherited the same genetic change then you would also be at risk of developing the condition during your lifetime. If you have not inherited the genetic change then you would not be at increased risk. For some conditions such as Huntington disease, it will not be necessary to test an affected family member first because scientists already know what changed gene to look for.

The decision to have a predictive test can be difficult, we discuss some of the most important issues to think about here.

Before you make a decision about genetic testing, it is important that you try and think through, and discuss with a genetic health professional, how all the possible results of the test might affect you emotionally. It is a good idea to try and imagine how you might feel if you were to receive good news or bad news and recall how you reacted to bad news in the past. Thinking these issues through may help you in deciding whether it would be better to live with the uncertainty of not knowing or whether it would be better to know, whatever the result might be. However, it is important to remember that we all react differently and there is no ‘normal’ reaction.

For some people, even a result which shows that they have the genetic change is preferable to the stress and anxiety caused by not knowing. For those people, having more ‘information’, whatever that information is, can be a relief.

Some people are relieved when they find out they are at high risk for a genetic condition, when it is something that can be treated. They feel that the information is useful as it means they can do everything they can to increase their chance of staying healthy. For others who have a genetic change that causes a condition that cannot be treated, it can be like finding out they have the condition already. The only question on their mind is ‘when exactly will it happen to me?’ This can be very distressing.

Some people experience a sense of shock when they find out they have the faulty gene. They may feel alone, anxious, angry or ashamed. Genetic specialists and other health professionals such as counsellors and psychologists, are experienced in helping people in these situations and can be a good source of support.

Some people also find it helpful to contact a patient association or support group. These groups can provide information about the condition and what it is like to live with it, including their experience with practical and emotional aspects. They can often put people and families in touch with others who are in a similar situation.

Finding out you have a changed gene and may have passed it on to your children can cause people to feel guilty and anxious about the future health of their children. It is important, however, to remember that genes are distributed by chance and having a faulty gene is no one’s fault.

For some people, finding out they are at high risk of developing a condition is like being on an ‘emotional rollercoaster’. They say there are good days and bad days. Most people do eventually come to terms with their result and use the information to help them make plans for the future.

For most people, finding out that you do not carry the faulty gene brings joy and relief. However, it is not unusual for people to say that they experience a low feeling after testing. This may be because they have lived with the risk for so long that it requires a major change to adjust to being ‘normal’. Some are disappointed that the ‘good news’ does not bring as many positive changes in life as they thought it would bring.

For some people who are convinced they do have the genetic change, finding out they do not can change their whole outlook on life. Some people find it difficult to deal with the idea of ‘having a future’.

Some find it difficult to communicate the ‘good news’ to their relatives. ‘Survivor guilt’ is something that is often reported by people who receive ‘good’ test results. They wonder why they ‘escaped’ when other family members did not. Sometimes it is difficult to accept that you have been fortunate when others have not.

Some people who receive ‘good news’ feel an increased responsibility to care for family members who are affected by the condition.

It takes time to adjust to the results of the test, even if the results are ‘good news’.

The results of your genetic test will not only tell you about your risk of developing the condition, it will also tell you more about your children’s risk.

If your test results show that you have not inherited the genetic change identified in your family, you are not at an increased risk of developing the condition, and your children will not be able to inherit the genetic risk from you. This is because you cannot pass on a faulty gene that you do not have.

If your test results show that you do have the genetic change, your children might also have inherited the genetic change and be at risk. A child should not usually take a predictive test until they are over 18 years of age. If there is no medical benefit in testing a child, it is considered best to wait until the child is old enough to make the decision for him or herself. The exception to this is when there is a specific medical benefit in carrying out predictive testing on a child.

Discussing a genetic condition and predictive test results with children and adolescents can be very difficult. They may have lots of questions and it is important to answer any questions as honestly as possible taking into account their age and maturity level.

For some genetic conditions, it is possible to perform a test during pregnancy to see if the baby has inherited the genetic change (prenatal testing). If you think this might be an option for you, speak to your doctor about whether these tests are available for the condition you are concerned about. It is essential you do this before the pregnancy if possible as the laboratory may have to make preparations that can take several months.

It may be possible to perform a technique called Preimplantation Genetic Testing (PGT) as an alternative to testing the foetus during pregnancy. This involves the couple undergoing medically assisted reproduction, after which the fertilised eggs are tested to see if they have the changed gene. For more information about PGT, and whether it is available to you, you should speak to your doctor.

In many cases the genetic testing process brings families closer together and the family can be a good source of support. 

In some cases however the process causes tension and complications within the family. It is a good idea to think through how the testing procedure, and the test results, might affect your relationship with your partner and other family members. Remember that an affected family member first needs to agree to be tested so that the genetic gene can be identified. Approaching a family member for this reason may be difficult. Sometimes family members have lost touch. It can also be difficult to talk about illnesses that have occurred in the past as it may bring back painful memories. Genetic specialists should be able to offer you advice in these situations.

Some people may want to know about their genetic risk status because of concern for their family members. Other family members however, may not want to undergo testing because they prefer not to have information about their risk. You will need to be sensitive to this because your test can provide family members with unwanted information about their risk. It is important to remember that members of the same family may have different feelings about testing, and that these feelings should be respected. 

Genetic testing may sometimes reveal family secrets involving adoption and non-paternity (that is, the biological father is not who the family thinks it is). This is because the process looks into people’s family history and it may become evident that you do not share your genes with your family members. This is a possibility you should be aware of before beginning the process.

Access to your genetic test results are confidential. Your doctor is not allowed to tell anyone that you have had a genetic test or pass on your test results without your permission.

Insurance companies often ask you to provide medical details about yourself and your family when you apply for an insurance policy, particularly above a certain amount. In the UK, there are only a few scenarios where companies can ask for this information. 

Living with a genetic condition can be difficult financially. Those living with a condition may be unable to work for long periods of time, or may have to stop working altogether. Partners and other family members may also find it difficult to juggle work with the responsibilities of caring for a family member or partner. For some people, knowing that they are at risk of developing a genetic condition allows them time to plan financial and other practical aspects of their future.

If you do decide to go ahead with genetic testing,it is sensible to choose a time when complicating factors from the outside are at a minimum. For example, periods with life-changing events such as marriage, childbirth, divorce, break ups,and stressful times at work are difficult times to undergo testing. 

It can be helpful to make a decision about testing even if it is not an absolute, for example ‘I will definitely not do it until I am at least 30’. In this way you can put the issue aside to look at again in the future.

It is a good idea to plan what you will do the day you receive your results as you may feel emotional, whatever the outcome.

Once you receive your test results there is no going back. This is why it is important to be very sure about the decision you make, and why it is important to discuss your decision with a trained genetic specialist. Remember that making an appointment with a genetic specialist does not mean that you have to go ahead with genetic testing.