Mon 5 Aug 2019
Consumer genetic tests used by thousands in UK.
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A recent report in the Guardian
highlights the dangers of using third-party interpretation services to analyse DNA data obtained from sources such as 23andMe or AncestryDNA. Some senior NHS doctors have called for a crackdown on consumer genetic tests following an influx of patients who have been wrongly told they are carrying dangerous mutations linked to cancer and other serious conditions.
The article points out that consumer genetics tests have had a surge in popularity in the past few years, with hundreds of thousands of people in the UK thought to have undergone testing. While the report focuses on issues arising in the UK, it’s reasonable to expect a similar situation occurring in Australia.
Here, consumers who are using 23andMe are restricted to the ancestry data alone and are prohibited from receiving the health-related interpretive data. This leads to an incentive for people who have spent the money on DNA analysis to see if they can get further value by sending the DNA data on to a third-party company for further interpretation in terms of health-related risks.
As the experts and clinicians quoted in the Guardian article point out, this can be a very misleading exercise. There is a very high risk of being given false-positive risk estimates from such analyses. The reason for this is that the DNA analysis being carried out for the ancestry studies is not designed to accurately detect other low-frequency mutations that may be associated with specific disease risks. For clinical diagnostic purposes a patient’s DNA is sequenced, i.e. the full genetic code is read out for the regions of interest. For ancestry studies, companies use DNA chips that detect the presence of scattered markers throughout the genome called single nucleotide polymorphisms or SNPs, they do not read the full DNA sequence.
Although the companies carrying out interpretation may make a statement saying that the findings should not be treated as a medical diagnosis, they may not point out the very high probabilities of false-positive and false-negative results in their risk estimates. As a result, consumers and some doctors may be unaware of just how unreliable such results can be.
NHS clinicians in the UK reported in the Guardian article cite cases of women planning mastectomies on the basis of false-positive BRCA mutation results, false diagnosis of inherited deafness genes and also of bowel cancer risk genes, all of which were disproved by NHS laboratory genetic sequencing.
BioRXiv Very rare pathogenic genetic variants detected by SNP-chips are usually false positives: implications for direct-to-consumer genetic testing
Regulation of Internet-based Genetic Testing: Challenges for Australia and Other Jurisdictions
NHMRC information for consumers