People should not make health decisions based on genetic tests they do at home, experts in the UK have warned. Anneke Lucassen, Professor of Clinical Genetics at the University of Southampton and colleagues have recently published a paper in the British Medical Journal entitled ‘Direct-to-patient genetic testing’. This describes the situation in the UK but is equally relevant here in Australia. They warn that results can be unreliable, the tests could be wrongly reassuring - or lead to unnecessary worry.
The Royal College of General Practitioners in the United Kingdom has advised that GPs who are consulted about a patient’s direct-to-consumer (DTC) test results should use clinical and family history to decide whether to make a referral to an NHS genetics specialist. The College’s Position Statement
about direct-to-consumer (DTC) genomic testing, written jointly with the British Society for Genetic Medicine, said: “The analytical validity, sensitivity and clinical utility of such testing may be much lower than is popularly perceived. For certain types of DTC results, there is a very high chance of false positive or false negative results. This means that patients should be offered the NHS care which would otherwise have been offered (for example, family history and risk assessment, healthy lifestyle advice, or referral to specialist care) regardless of their DTC result.”
Most DTC testing fits into one of four categories as described in the BMJ article:
Polygenic risk scores
—combine many different common variants across the genome to place someone in a broad risk category, e.g., “your genes predispose you to weigh about 3% more than average.” The validity and utility of these risk scores for predictive clinical purposes is hotly debated. In our opinion, although polygenic scores may be useful in researching the causes of disease, or stratifying populations into higher and lower risks, they are rarely able to usefully predict disease.
Genotype at specific points
—looks at specific variants that influence the chance of developing particular diseases, e.g., “you have two copies of the ε4 variant in the APOE gene. People with this result have an increased risk of developing late onset Alzheimer’s disease.” This type of testing can also be used to identify variants that affect drug metabolism.
—looks at specific variants to identify people who are carriers for particular recessive genetic conditions, eg, “one variant detected in the CFTR gene. If you and your partner are both carriers, each child may have a 25% chance of having this condition.” Many carrier tests are ancestry specific: they test for specific carrier variants common in a particular ancestral group. If someone with a different ancestry were a carrier, this would probably not be detected as it would likely be due to a different carrier variant (which the test would not check).
Uninterpreted “raw” genetic data
—some DTC genetic test companies provide access to uninterpreted genetic data. Customers can download their data and seek an interpretation using third party services. These usually work by cross referencing the data against freely available genetic databases and constructing a report based on interpretations in these databases (which may not be up to date). They may report variants and disease risks that were not reported or referred to by the original DTC genetic test company, and might repurpose raw data from tests designed to answer other questions, such as ancestry, to try to provide health information. We have previously discussed
the risks associated with this type of interpretation.
The authors write that false positive and false negative results are common and even if a true positive finding is made, the predictive value of the results is low if there is no family history of the disease associated with the genetic variant. What this means is that most people who carry the gene but do not have a family history have a low risk of being affected by the disease in the future. Other unknown genetic variants, lifestyle and other environmental factors may all play a very large role in what happens in the future.
Articles from the University of Melbourne and Monash University
are worth reading because they cover the pitfalls of DTC genetic testing in Australia.
Online Direct-to-Consumer Genetic testing in Australia (Monash University)
WHAT DO WE NEED TO KNOW ABOUT ONLINE GENETIC TESTING? (Melbourne University)
BMJ article on DTC genetic testing