Genetic Testing

What is Genetic Testing?
It is the analyses of an individual’s DNA. There are different types of genetic tests and different methods of testing.

What is DNA?
Deoxyribonucleic Acid (DNA) is made up of different sections that contain specific codes to make proteins. These are our genes. The proteins produced are our body’s information on how to develop, maintain normal function of our cells and stay healthy.

Why can it cause a problem?
We all have the same number and sequence of genes. There can be small DNA differences between individuals meaning the same gene will send different messages to our cells which makes everyone unique. These differences in our DNA can affect how an individual develops from being an embryo to adulthood and can affect how we can be susceptible to different conditions. This is normal variation, known as polymorphisms.

However, some variations can result in the gene codes for the wrong protein or does not code for a protein at all. This means the gene does not work and this can cause development or health problems. There are different ways of describing this that all mean the same thing – it does not work properly: a gene mutation, gene change, gene fault, pathogenic mutation or pathogenic variant.

How are genes tested?
A sample of body tissue is needed. Although blood samples have traditionally been the best method of obtaining DNA, it is now possible to use buccal (cells from inside the cheek) swabs, saliva. However, sometimes enough DNA may not able to be extracted from samples other than blood.

The gene sequence can be examined to determine if it is correct or incorrect. There are different methods of testing. These include genomic testing and targeted genetic testing. When testing for cancer predisposition genes, either direct sequencing of one gene or a panel of genes that are known to cause a similar cancer predisposition can be used. Which type of test to use is informed by the cancers that have occurred in a biologically related family or an individual.

What types of genetic tests are there?
There are many different types, and the two of relevance to inherited predisposition to cancer are;

  • Diagnostic
  • Predictive

Diagnostic Testing
Genetic testing is used to diagnose a condition. It is best practice to identify a gene mutation in a person most likely to carry it i.e. a person affected by a cancer that fulfills criteria to suspect they may have a cancer predisposition gene fault. This is the best way of being able to inform them and their family about the result and its meaning.

This type of test can take varying lengths of time dependent on the type of test. In general it will take around 8 weeks. Some may be able to be done more quickly, particularly if any treatment is dependent on the result, but this cannot be guaranteed.

Predictive Testing
This type of genetic test looks for a specific mutation in one gene that has already been identified by a diagnostic test in a close relative. This means that the gene is known and the risks associated are well described. This provides risk information to that family member about how likely it is they may develop the associated condition. It is not diagnostic of the actual health problem.

There are many issues to consider in having a genetic test and full discussion of the potential meaning of a result and impact, with a Genetic Counsellor is important.

What are the potential outcomes?
This is dependent on the genetic test used (single gene or panel test) and whether it is a diagnostic or predictive test. This will be discussed with you by the Genetic Counsellor.