Genetic tests that claim to predict risk of illnesses miss most cases

Over the counter genetic tests that claim to predict the risk of illnesses such as heart disease and cancer ‘miss nine in ten cases’

  • The genetic tests only identified 10 per cent of eventual breast cancer cases 
  • It also produced as many as one in 20 false positive results, causing worry 

Genetic tests which claim to predict the risk of illnesses such as heart disease and cancer miss nine out of ten cases, a major study found.

Analysis of polygenic risk scores – which use genetic variations to estimate a person’s chances of health conditions – found they ‘performed poorly’ at identifying cases.

One in 20 also resulted in a false positive – when a person is wrongly diagnosed as having disease – causing worry and the potential for unnecessary tests and treatment.

Negative results could also be ‘falsely reassuring’ to patients, doctors warned.

The commercially available tests are often billed as a breakthrough that could transform the prediction and prevention of common diseases.

Over the counter genetic tests were found to perform poorly at identifying cases of heart disease and cancer

But in an assessment of 926 polygenic risk scores for 310 diseases, University College London researchers found they typically identified just 11 per cent of individuals who went on to develop disease.

For breast cancer, they only identified 10 per cent of eventual cases, along with 12 per cent of cases of coronary artery disease, a leading cause of heart attack and stroke.

At the same time, they wrongly suggested 5 per cent of people would develop a disease who did not, which could have huge ramifications for the health service.

Experts warned that if used widely – for example as part of a national screening programme – the tests would result in more false than true positive predictions.

Professor Aroon Hingorani, of the UCL Institute of Cardiovascular Science, who led the study, said strong claims have been made about the potential of polygenic risk scores in medicine.

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‘Our study shows that this is not justified’, he said.

‘We found that, when held to the same standards as employed for other tests in medicine, polygenic risk scores performed poorly for prediction and screening across a range of common diseases.

‘On the evidence we’ve looked at we couldn’t see a place for these tests in screening.

‘The important thing with many of these conditions like heart disease is that where we’ve got safe and effective preventative treatments like diet and lifestyle as well as statins and blood pressure lowering medications, we could achieve more from using these more widely.’ The researchers also investigated how polygenic risk scores would perform if used alongside conventional screening methods.

They found if used alongside conventional risk factors, several thousand people would need to have a polygenic risk score done to guide statin prescriptions to prevent one additional heart attack or stroke.

Using age alone as a guide to statin prescription would be simpler and more effective at preventing heart attacks and strokes without the need for genetic testing, they said.

Adding these risk scores as first stage screening to determine who should be prioritised for a mammogram would miss most women who later develop breast cancer.

It would also generate many false positives adding to the burden on healthcare systems, according to the findings published in BMJ Medicine.

Co-author Professor Sir Nicholas Wald (UCL Institute of Health Informatics) said: ‘It has been suggested that polygenic risk scores could be introduced early on to help prevent breast cancer and heart disease but, in the examples we looked at, we found that the scores contributed little, if any, health benefit while adding cost and complexity.’

Available for patients and companies to buy online, Dr Jasmine Gratton, of the UCL Institute of Cardiovascular Science, said polygenic risk scores have grown in popularity.

She said they ‘seem attractive because genotyping is now inexpensive, the same for all diseases and is performed only once because a person’s genotype does not change.

‘However, these features are irrelevant if the test is not useful,’ she added.

However, Professor Michael Inouye and assistant Professor Sam Lambert of Cambridge University, lead authors of the PGS Catalog which was looked at in the study, defended the tests.

They said they had ‘potential utility in many different clinical use cases’ and other studies use the system ‘in more flexible ways’.

They said: ‘The current paper generally takes a narrow view of how polygenic scores can be used.’

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