Genetic testing: blood or saliva?
Tasmyn Scriven explains the pros and cons of both saliva and blood sample testing for genetic analysis.
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Germline mutations are genetic changes that occur in the DNA of germline cells (eggs and sperm). These mutations can be inherited from one or both parents and are present in every cell of your body. Germline mutations can lead to a wide range of genetic disorders and can increase the risk of developing certain diseases or conditions, such as inherited breast and/or ovarian cancer.
If you have breast or ovarian cancer, you may be referred to a genetic counsellor who will review your medical and family history information. Based on this, the genetic counsellor may recommend genetic testing to identify mutations in genes that increase the risk of breast and ovarian cancers. This information can be used to guide medical decisions, such as increased screening or preventative measures, or to provide information for family planning.
Genetic testing for inherited breast cancer involves analysing your DNA to identify mutations in genes that are associated with an increased risk of developing breast and/or ovarian cancer.
The most well-known genes associated with inherited breast and ovarian cancer are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2). The BRCA1 and BRCA2 genes function as tumour suppressor genes and account for approximately 50% of inherited breast cancers. Mutations in these genes are known to increase the risk of developing breast and ovarian cancer in women and breast and prostate cancer in men. However, there are other genes that can also increase the risk of developing breast and ovarian cancer.
Who should have genetic testing?
Genetic testing for inherited breast cancer is typically recommended if you have a personal or family history of breast cancer, especially if the cancer occurred at a young age or affected multiple family members.
The testing process involves collecting a saliva or blood sample (non-tumour cells) and analysing the DNA for mutations in specific genes.
Saliva and blood samples are both commonly used for genetic testing for inherited breast and ovarian cancer, but there are some differences between the two approaches. Saliva testing involves collecting a sample of your saliva in a specialised container. In contrast, blood testing involves drawing a blood sample from your body.
In both scenarios, the samples are sent to a laboratory for genetic analysis. DNA is extracted from the epithelial cells in the saliva sample or from the white blood cells in the blood sample. Following DNA extraction, the laboratory will analyse the specific genes associated with inherited breast and/or ovarian cancer.
Saliva is often preferred for genetic testing as it’s a non-invasive procedure. It’s easy to collect and painless, especially if you don’t like needles. Saliva can also be collected anywhere, even in your own home. Saliva samples are more stable than blood samples during transport and can be shipped at room temperature. Additionally, the DNA extracted from saliva is generally stable and can be stored for long periods of time. This is especially advantageous when sending samples to overseas laboratories.
In some cases, blood samples are preferred as blood typically contains more DNA than saliva. This may be necessary for certain types of genetic testing, like when testing for genetic mutations associated with haematological (blood) cancers.
Additionally, chemotherapy can affect the quality of DNA in cancer cells and other tissues, so blood may provide a more reliable source of DNA for genetic testing in this case. However, shipping blood samples can be more challenging due to regulations around the transportation of biological samples.
Both are effective
Overall, saliva and blood are both effective and reliable samples for identifying genetic mutations associated with inherited breast and/or ovarian cancer. The choice between providing a saliva or a blood sample may depend on your preferences, the specific requirements of the specific laboratory and the genetic testing that is being performed. Genetic counsellors are trained professionals who are able to provide guidance on what sample is best for the patient.
MEET THE EXPERT – Tasmyn Scriven
Tasmyn Scriven is a genetic counselling intern at the Division of Human Genetics at the National Health Laboratory Service. She is passionate about raising awareness of the genetic counselling profession and increasing access to genetic services within SA.
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