1.1 What is Genetic Testing?
Genetic Testing:
There are many reasons a person might have genetic testing. Some examples include: a child with developmental delay, a person with a strong family history of illness, and a person with clinical symptoms suggestive of a genetic condition.
- is the analysis of an individual's genetic material.
- can be used to gather information about an individual's genetic predisposition to a particular health condition, or to confirm a diagnosis of genetic disease.
- is done by analyzing small samples of body tissue (e.g. blood, cheek swabs).
There are many reasons a person might have genetic testing. Some examples include: a child with developmental delay, a person with a strong family history of illness, and a person with clinical symptoms suggestive of a genetic condition.
1.2 Availability of Genetic Tests
In Australia, genetic testing is available for more than 400 different complex diseases including hereditary breast, stomach, and bowel cancer, heart disease, deep vein thrombosis, melanoma, diabetes, liver disease, kidney disease, cystic fibrosis, amyotrophic lateral sclerosis, various inherited neuropathies and some dementias (such as Huntington’s disease and early onset Alzheimer’s disease).
The tests are designed to calculate an individual’s genetic predisposition to a number of different health conditions. The tests also provide ancestral information and some even provide individuals with the opportunity to compare their genes with friends, family and others, provided there is mutual consent.
Test results display potential genetic risks only and do not act as a medical test or diagnosis.
The Australian Therapeutic Goods Administration (TGA) is responsible for regulating medicines, medical devices, blood and tissues, and only requires genetic tests to be listed on the Register if the companies are based in Australia and the tests are used to determine the susceptibility of an individual to diseases.
However, a number of overseas companies offer online Direct-to-Consumer genetic tests. Consumers can order test kits over the internet and send off a DNA sample (usually saliva or a cheek swab) to an overseas laboratory for analysis. The results are available to the individual over the internet after several weeks. These tests are currently unregulated in Australia and thus the quality and reliability of the results vary. Counselling is rarely offered.
Presymptomatic testing is available for a number of neurodegenerative diseases such as Huntington’s disease and some forms of cancer. Predictive testing is available for inherited conditions such as an inherited predisposition to haemochromatosis or breast cancer.
Genetic tests will no doubt become a routine part of health care in the future. Increased genetic testing makes it more likely that researchers can develop more effective treatments for a wide range of hereditary diseases, and can also help in early diagnosis (perhaps leading to preventive and even life-saving treatment).
For example:
- If you know you have a predisposition to bowel cancer, you can start screening earlier than the recommended age of 50.
- Similarly, if you know you have a genetic predisposition to breast cancer, you may decide to have prophylactic surgery, (removal of breasts and ovaries).
- If you have a genetic predisposition to macular degeneration (eye disease), then you could stop smoking cigarettes to try and mitigate onset.
- If you have a predisposition to deep vein thrombosis, then when travelling by aeroplane you would ensure you move around regularly and avoid caffeine and alcohol.
1.3 Limitations of Genetic Testing
While taking blood or tissue samples for genetic testing may cause minimal physical harm, information gathered from genetic tests is not just about individuals - it has significant implications for all of one's blood relatives.
There will be a number of years during which we will be able to identify individuals with an increased risk to develop certain diseases, but we will be unable to prevent or cure the disease. While some genetic tests may provide information about the nature of the condition that the person has, will develop, or for which they are at increased risk, they can rarely predict the age at which symptoms will first appear or how severe the symptoms will be.
For example, if a woman knows that she has inherited a gene that means she has a predisposition to develop breast cancer, that does not tell her if she will ever develop the condition and if she does, when it will occur and how severe it will be. Also, most women who develop breast cancer (85 to 90%) do not have an inherited genetic susceptibility to the disease; the so-called breast cancer genes are only one factor causing the disease. In prenatal testing, a genetic test typically can’t predict the severity of a particular condition or the potential quality of life for the child.
Moreover, an individual is much more than the sum of their genes. Genes interact with one another in ways that we do not yet understand and the environment can also modify the expression of genetic messages to the body, together with other contributing factors that are not genetic at all. Many people who test positive for genetic mutations associated with certain conditions never develop those conditions.
A number of environmental factors, along with genetic make up, ultimately determine whether you will develop a health condition.
