GPs have been urged to warn patients of the potential dangers of using OTC genetic testing kits, as falling prices make them more affordable.
Genetic kits are now available in shops for less than £300, having cost thousands of pounds when they launched.
Dr Imran Rafi, chairman of the Primary Care Genetics Society and a GP in Surrey, told GP that the kits were becoming increasingly popular as more companies entered the market.
The rise comes despite a report by the Human Genetics Commission in 2007 which called for the restriction of advertising for genetic testing.
The report also recommended that genetic tests should only be offered by suitably qualified health professionals.
Dr Rafi said: 'GPs should urge caution with these tests. It is important that they have a discussion about the potential harms with their patients.
'They should take a family history and be particularly aware of high-risk families, who have a strong family history of diseases.'
Most GPs should be able to interpret the result of genetic tests, usually given in terms of relative and absolute risk, Dr Rafi said.
'The problem with these tests is that they use early research findings to identify single nucleotide polymorphisms (SNPs) that are common to diseases such as cancer and arthritis.
'It is unclear what research these tests are based on, so it is important that GPs look at the research behind the results.'
The tests will create problems not just for GPs but also for specialist genetic services.
'The patient will get a printout showing them a whole range of diseases. The concern is that they will be swayed by this information,' warned Dr Rafi.
'They will then require genetic counselling, which is provided by the NHS but not by the genetic test companies.'
Brian Whitley, managing director of the London-based genetics company GeneticHealth, said: 'Tests can be misleading to patients if the results are not properly explained to them. We offer our patients a face-to-face consultation with a doctor to discuss the findings.
'We offer tests that allow patients to identify their risk of common diseases. Informing patients that they might have an increased risk of developing a condition can allow them to make lifestyle changes like giving up smoking.'
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