By Emma Wilkinson
Health reporter, BBC News
Scientists say they are beginning to make real progress in pinning down the genetic basis of common diseases.
Genetic testing is a rapidly growing market
In the past six months alone there have been reports of key genes involved in diabetes, heart disease, bowel and breast cancer, dementia and obesity.
And subsequently there has been an explosion of companies offering gene tests to predict a person's future risk of life-threatening disease.
But how useful are such tests and could they do more harm than good?
Christine Patch, consultant genetic counsellor at Guys Hospital in London and member of the Human Genetics Commission, believes the science is not yet strong enough to support the multiple gene tests on the market.
"You're wasting your money," she said, adding that such tests were not without disadvantages.
"The risk is the anxiety caused by saying someone is a high risk.
"I also think there's a risk of false reassurance - if you tell someone they are at low risk of heart disease that may cause someone to continue drinking alcohol and eating saturated fats."
The commission is due to publish a report on Tuesday calling for tighter controls on tests to make sure they are based on sound evidence and not making unsubstantiated claims.
In a previous report, they recommended that predictive genetic tests should only be available via a consultation with a doctor and, like prescription medicines, should not be advertised directly to the public.
Dr Patch said many tests will not tell an individual anything more than they would know from just looking at their family history.
"We wouldn't use these tests on the NHS, where we have to get value for money," she said.
Many companies in the US and Europe offer gene tests for conditions such as diabetes, heart disease and cancer.
And others are coming on the market that scan all 500,000 genetic variants to give an individual a picture of their risk of several diseases at once.
Dr Paul Jenkins, consultant endocrinologist and clinical director of Genetic Health - a UK company offering a variety of tests - said it was an evolving field.
"But we believe the science is strong enough to offer individuals broad risk assessment of their genetic predisposition to many of our common age related diseases.
"In order to avoid inappropriate anxiety or concerns we ensure all of our clients receive a medical consultation with a consultant to put their genetic results into context."
The company also said they turn away clients with unrealistic expectations and would encourage more regulation of tests.
Dr Paul Pharoah, senior clinical research fellow at Cambridge University Cancer Centre, said such tests were not yet clinically meaningful.
"The science is at the preliminary stage, we only know about a handful of genes.
"The number of companies [offering tests] has gone up rapidly in the past 12 months because we are starting to find genes that are really associated with disease.
"But the likelihood is there's hundreds of genes for every disease.
"To start counselling people about their risk and how they should modify their lifestyle to modify that risk is effectively ludicrous. It's not good science."
Stuart Hogarth, from the Institute of Science and Society at University of Nottingham, has spent the past few years looking into how such tests are regulated.
He said there were not enough controls in place to ensure people were not being misled.
"We still do not have the regulatory framework. We haven't developed any standards to indicate to companies what kind of data is needed before they bring something to market."
Such tests are covered by an EU directive but because they are deemed low risk, they are not subject to a review before they are marketed.
This means there is no obligation for companies to provide evidence to support the claims they make, he explains.
Many experts, including the Human Genetics Commission, think the genetic tests should be classified as higher risk meaning they would be subject to greater controls.
"We have no way for consumers to separate good tests from bad tests and there is a severe danger of losing public confidence - all that's left is we're asking consumers to be sceptical.
"But some companies are doing a much better job than others," he said.
He added that in the past year researchers have made real progress in the science but more research was needed.
Professor Shirley Hodgson, an expert in cancer genetics at St George's University of London, stressed there are very useful genetic tests such as the BRAC1 test for breast cancer.
"I wouldn't want people to devalue these tests because we are throwing these relatively low value tests at them."
She added that people needed proper genetic counselling in order to process the results.
One man she had seen in her NHS clinic had been incredibly anxious after paying for a test which suggested he had an increased risk of a variety of cancers.
"I didn't think his genotype was important but he was in a state of collapse.
"The other thing was it had left him with very little he could do."
One of the main concerns of those who work as genetic counsellors is that people need to fully understand what the risk means.
Especially as we know so little about the link between environment, lifestyle and genes.
Dr Pharoah said a more realistic use for gene tests would be to lower the age at which someone was screened for breast or colon cancer.
"We're almost there for these diseases but these are very specific examples."