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Jnetics, PO Box 65520, London N3 9BU

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Predictive Genetic Testing

What is a predictive genetic test?

This refers to a test used to identify the presence of a specific mutationA mutation refers to a structural change in a gene. It can be an alteration to a gene’s size, arrangement, or molecular sequence for a genetic disorder in a person that is not currently showing any symptoms but is at risk of developing the disorder later life.

This type of testing is largely used for dominant conditionsDominant disorders require only one copy of a specific disorder-related mutation to be passed onto their child for the disorder to be inherited e.g. DYT1 generalised dystonia and breast/ovarian cancer (BRCA1 and 2).

How can predictive testing be arranged?

If you have a family history of a genetic condition that may develop in the future even if you are not showing any symptoms now e.g. DYT1 generalised dystonia and breast/ovarian cancer (BRCA1 and 2), you may ask your doctor to refer you to your regional genetics service to discuss genetic testing.

For ethical reasons, predictive testing for adult-onset disorders is discouraged in children where there is no medical intervention available.

Things to consider prior to having predictive testing

Predictive testing may have the benefit of identifying a potential increased risk of a disorder for which monitoring or early intervention may have a positive impact on disorder progression.

It is important to note that a number of disorders have reduced penetrance, including generalised dystonia (DYT1) and breast/ovarian cancer (BRCA 1 and 2).  As such, having the gene mutation means that you will have an increased risk of developing the disorder in later life but it is not a certainty. For more information, the section on breast/ovarian cancer (BRCA 1 and 2) provides a good example of condition that has reduced penetrance.

Because the health and family implications of predictive testing can be complex and significant, it is important to meet with a genetic counsellor.  For more information about the purpose, benefits and how to contact a genetic counsellor, please refer to the genetic counselling section.