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21 August 2014

Why DNA testing isn’t always best for customising medical treatment

Greater understanding of the genetic causes of illness suggests that this method of categorisation might not be the most accurate.

By George Gillett

If doctors discovered you had a 30 per cent chance of developing colon cancer, would you want to know? What if that probability was only 10 per cent, or perhaps as high as 50? Maybe it would depend on what you could do to improve your prognosis – or whether the information would be confidential.

These ethical issues are becoming increasingly relevant following the announcement this month of a landmark £300m project to sequence the genomes of 100,000 NHS patients. The programme, which will last four years, is part of the developing field of personalised medicine and it aims to use genetic data to customise medical treatments.

Currently, many diseases are defined by their symptoms or the site of occurrence. Greater understanding of the genetic causes of illness suggests that this method of categorisation might not be the most accurate. For instance, scientists now believe that cancer is better understood as a plethora of diseases rather than a single one because of the variety of underlying genetic mutations.

Improved awareness of these genetic factors raises the potential of new treatment options. Up to one in four cases of breast cancer is caused by a mutation in the gene that encodes the HER2 protein. As such, Herceptin, the drug used to target the protein, is given only to breast cancer patients with this genetic abnormality. It is hoped that further research will allow more drugs to be optimised in a similar way.

Personalised medicine could also be safer. Genetic variation among patients has been linked to dangerous reactions to drugs. In 2004, a British Medical Journal report estimated that each year in the UK, more than 10,000 deaths result from adverse reactions to drugs. By predicting how patients will respond to medication, genetic screening could help avoid these cases.

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There is also the possibility of disease prevention. If we know which diseases we are most susceptible to, that allows us to take precautions. For instance, a patient might choose to have surgery to remove her ovaries after discovering that she has a genetic predisposition to ovarian cancer. These changes can also be more subtle. Health advice can often seem overwhelming; genetic testing could personalise dietary guidelines or fitness regimes for individuals.

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These exciting developments bring challenges. A 2001 study found that genetic testing had certain severe psychological implications, with a group of adults reporting clinical levels of anxiety and depression after learning that their genes predisposed them to colon cancer. Especially when it comes to conditions for which effective treatment isn’t available, it’s worth asking yourself how much of your genome you wish to explore.

Another concern often raised is the legal status of genetic data. In 2008, the US government introduced the Genetic Information Nondiscrimination Act to prevent employers and health insurers requesting genetic records. In the UK the government relies on a voluntary agreement with the Association of British Insurers. This expires in 2017 and a review is due this year.

That said, if you wish to discover your medical fate you needn’t wait for the NHS project. Private companies already offer genotyping services for less than £100.