Australasian Science Magazine

By Ken Harvey

The promises of genetic tests and treatments may be outstripping the science.

When you enter a Chemmart pharmacy, it’s hard to miss the posters and brochures promoting its “revolutionary myDNA test”. The brochure states that it’s “personalised medicine” where “your DNA results … can help guide your future health and lifestyle choices”.

Advertising on both the Chemmart and myDNA websites claims that “70% of people who take the test have a finding that could affect current or future medications”.

It’s said you should consider the test if you’re taking anti­depressants, pain or reflux medication. The test also covers those who take blood thinners such as warfarin. It’s said to be particularly relevant if you have a history of not responding to common drugs, you experience side-effects from your current medication, you take multiple medications, you have children on prescribed medication, or you are pregnant or planning pregnancy.

The test identifies common variations in the genes encoding some enzymes that metabolise a number of drugs (Table 1).

The test costs $149 but is not covered by Medicare or private health insurance rebates. It involves a cheek swab taken by a trained pharmacist that is sent to a lab for DNA analysis. The pharmacist receives $15 per test, with $30 going to Chemmart and the rest to myDNA. The results are delivered by a personal consultation with the trained pharmacist and are also sent to your nominated doctor. If changes to medication are recommended you will be referred by the pharmacist to your doctor.

The Science
Pharmacogenomic/genetic (PGx) tests are moving from scientific discovery to clinical implementation. Inherited variation in approximately 20 genes affecting around 80 medications may predict a patient’s likelihood of experiencing an adverse event (e.g. through poor metabolism of some drugs) or non-responsiveness to a given drug due to ultrarapid metabolism.

However, the cost-effectiveness and clinical utility of these tests is still uncertain. In addition, the scientific basis of the role of genes in the response to drugs is incomplete and rapidly changing.

A “normal” PGx test does not necessarily mean that you are not at risk for adverse events or non-response because current tests only capture known variants of known genes. Different companies providing these tests may report on different sets of known gene variants, and validation of laboratories and regulatory oversight in Australia is incomplete.

More traditional considerations, such as drug–drug interactions, drug allergy and dosing taking into account age, body weight, renal and liver function are still more important in optimising therapy than genetic considerations. In addition, many GPs currently have limited understanding of how to interpret such tests.

The blood thinner Warfarin is one example. Some studies have shown a reduction in adverse effects when starting doses of warfarin were changed by taking into account genetic variations of CYP2C9 and VKORC1, but the results have been mixed. At present, routine use of a genetic test to guide warfarin dosing is not recommended.

The Verdict
I believe Chemmart has overstated the role and value of this test. Instead of the broad claim that “myDNA is a genetic test that identifies which medications will work best for you,” I think they should have pointed out that the test is only applicable to certain drugs in particular situations.

I dispute that the test is “particularly relevant” to those who “take multiple medications, have children on prescribed medication” or “are pregnant or planning pregnancy”. These concerns have been submitted to the Therapeutic Goods Advertising Complaint Resolution Panel for an independent determination.

At present, the routine use of genetic tests to guide drug dosing is not recommended. Consumers should discuss the usefulness of this test with their GPs before handing over their $149.

Ken Harvey is an Adjunct Associate Professor in the School of Public Health and Preventive Medicine at Monash University, and an executive member of Friends of Science in Medicine.