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AM News

Genetic Testing in Primary Care

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  • Genetics testing has taken off over the last 20 years, with the human genome having been fully mapped in 2003.
  • Companies are now starting to market genetic tests straight to patients; some GP’s (non-specialists) are also offering these tests through their surgeries.
  • As with most new things in medicine, genetic/DNA tests are being over-hyped through the internet, by the companies wanting to make money out of them.
  • Clients should think very carefully before considering genetic tests; e.g. the presence of a cancer gene does not necessarily mean that a cancer is inevitable, rather just an increased probability; what does it mean if nothing can be done to improve the outcome anyway?
  • Consider that there may be implications for employment or life insurance costs, if findings are adverse.

Examples of where genetics testing is tried and tested, and known to be useful:

  • Strong family history of breast cancer – relatives with breast cancer at a young age, or multiple relatives affected. Your GP can follow guidelines and, when necessary, refer you to the Clinic Genetics service at King Edward Memorial Hospital to further explore your risk.
  • Deep Vein Thrombosis. In some cases, if there has not been an obvious trigger, your GP may send tests to look for inherited clotting defects, which may indicate that you need to take preventative measures lifelong.
  • Diagnosis of haemochromatosis (a condition causing overload of iron)
  • Strong family history of ovarian, colon, or endometrial (womb) cancer

Non-Invasive Pre-natal Testing (NIPT):

  • A blood test can be taken from the pregnant woman from around 10 weeks gestation. Samples are currently sent to America or China and give a result within about 2 weeks.
  • It is a very accurate test for the detection of Down’s syndrome, and Edward syndrome, and less accurate for Patau syndrome.
  • It is expensive, between $500-$1400
  • Tests can fail; and if positive need to be confirmed by an invasive test (amniocentesis or chorionic villus sampling)
  • By comparison, the current Down syndrome screening program consists of a blood test and ultrasound at 11-13 weeks and has a detection rate for Down’s syndrome of 90% and a false positive rate of 3%. The ultrasound part of this test is also useful in many other ways – confirming dates, diagnosis of multiple pregnancies, detection of anatomical problems, etc. Therefore NIPT should not be thought of as a replacement for first-trimester ultrasound and blood testing.
  • The situation is rapidly developing, but at the present time there are no Australian guidelines as to who should be offered the test. We would recommend discussion with your GP or obstetrician on an individual basis.

Direct-to-consumer DNA testing.

  • DNA testing kits are sold direct to the public without the involvement of a doctor
  • The promotion is that it gives individuals “complete control over their health”
  • Labs are often situated overseas, predominantly in the US, leading to difficulties should legal redress be required
  • The US Food and Drug Administration (FDA) have restricted the practice, or closed, some labs due to major concerns. We have no way of knowing the quality of the lab performing the work, and therefore the accuracy or meaningfulness of the tests.
  • Examples:
    • Sickle cell defect: This is straightforward, as it gives a simple “yes/no” answer – but testing for Sickle cell disease is already available through Medicare.
    • BRCA breast cancer genes (BRCA 1 and 2). Hundreds of different mutations that may influence risk, so understanding and interpreting a result is highly complex. This is better handled though Clinical Genetics services on an individual basis.
    • Type 2 Diabetes. Generally not useful; tests are derived from population studies comparing the frequency of certain DNA markers in T2D patients versus the normal population. These DNA markers are not the causative genes and tests do not take into account other, more important, factors such as diet and obesity. Therefore the information has limited meaning for an individual.
  • From the perspective of a GP, if we are asked to interpret the results of such a test (which we perhaps did not order), it is likely that we will find it very difficult to give meaningful advice. Indeed a recent survey of Australian genetics specialists, the experts in the field, revealed that only 7% would be confident in interpreting and explaining the results of these tests. Therefore, any GP promoting these types of tests should be treated with a level of caution.
  • Our advice would be to not be tempted by the marketing hype of Direct-to-consumer DNA testing until there is clear evidence of benefit to you.
  • See http://www.nhmrc.gov.au/your-health/genetics-and-human-health/genetic-testing-and-applications/direct-consumer-dtc-dna-tests for useful information published by the National Medical Health and Research Council.