Direct-to-consumer (DTC) genetic tests provide an inaccurate prediction of disease risk and offer little benefit to consumers, scientists claim.
Researchers from the Erasmus University Medical Centre in the Netherlands and Harvard Medical School, USA examined two currently-available tests and found results varied widely depending on the calculation methods used.
Professor Cecile Janssens and team examined the risk predictions supplied by two DTC companies, deCODEme and 23andMe. The researchers simulated genotype data for 100,000 individuals based on established genotype frequencies and using formulas and risk data provided by the companies, and obtained predicted risks for eight common multi-factorial diseases.
Some tests using deCODEme and 23andMe risk models calculated risks higher than 100 percent for five out of eight diseases. 'This in itself should be enough to raise considerable concern about the accuracy of these predictions - a risk can never be higher than 100 percent', researcher Rachel Kalf explains. Predicted risks higher than 50 percent were frequently observed for one company, but were less common in company two.
For Age-Related Macular Degeneration (AMD), the disease with the highest predictive ability, both companies assumed the population risk to be around eight percent. Of all subjects designated as having an increased risk, 16 percent from 23andMe and 19 percent from deCODEme's, would develop AMD, compared to the four percent found in the rest of the population studied. 'So individuals in the increased risk group may have a four-fold increased risk of disease, but they are still far more likely not to develop the disease at all', said Professor Janssens.
Furthermore, the tests studied genetic factors only, however many diseases are influenced by lifestyle and environmental factors. 'For complex diseases, if you ignore these non-genetic factors, you are looking at only a small part of the picture and missing the main story', Professor Janssens added.
This has triggered calls for tighter regulations surrounding DTC genetic testing, with critics saying the tests are a waste of money while also potentially misguiding people with regards to future health problems.
However, Kari Stefánsson, chief executive of deCODEme, queried the research findings saying: 'We never report a lifetime risk over 90 percent. This is not how we use these models'.
The research was presented at the European Human Genetics Conference in Amsterdam, May 2011.