05.Genetic testing explained
“Bad” genes in our genetic makeup (our inherited DNA) may increase our chances of getting a certain disease. There are two ways to find out if you are at risk:
- by looking at your family history for patterns of genetically determined (inherited) diseases
- by having a genetic test for suspect genes linked to the specific disease.
However, we couldn’t afford to test everyone to see if they might get one of the top 30 diseases, and many diseases with a genetic component are the result of several genes interacting, so finding the “main” gene doesn’t always tell you a lot anyway. If genetic testing is suggested, it’s usually being done to confirm or refute a strong suspicion of inherited disease from your family history and/or ethnic background. If your family history shows an increased risk of breast cancer, genetic testing might be offered.
Women who carry BRCA1 and BRCA2 gene mutations are at high risk of developing breast and ovarian cancer and a personalised “screening” program may include mammography and /or ultrasound, and even checking for ovarian cancer. Screening may begin at a much earlier age than for “average risk” women – usually five years before the age at diagnosis of the nearest relative.
Issues raised by genetic testing
Genetic testing can raise tricky issues, so counselling is advisable before going ahead.
- If the test is positive, and there is no treatment, such as with Huntington’s disease, will you feel worse?
- Companies providing life or disability insurance may ask you for any genetic test results. If you do not know, you can answer questions honestly without losing policy benefits.
- If a young person tests positive for significant mutations, this has significance for close relatives, especially parents.
Genetic testing costs
For women with a high risk of breast cancer, genetic testing may be covered by the state health department. If the criteria for a free test are not met, the cost for a comprehensive check of BRCA1 and 2 can cost about $2000. This cost reduces for other family members who want to be tested to about $275.
Some exceptions to population genetic testing
For now, good arguments for whole-of-population genetic testing only apply in relation to pregnancy and newborns. Parents could be tested when planning a pregnancy for the cystic fibrosis gene, and if both have it, testing of the foetus can be done. Down syndrome testing is an example of testing during pregnancy for a genetically based abnormality. The newborn or Guthrie tests don’t actually involve DNA analysis; they look for protein markers in the blood that may indicate genetically inherited conditions.