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Major personalised medicine test may be pointless

Proponents of genetic medicine are being warned not to be “overzealous” in selling the benefits of personalised treatments, as a new analysis appears to show that an FDA-backed test may be ineffective.

Testing for the CYP2C19 genotype is used to identify people who may not be suitable for treatment with the cheap blood thinner clopidogrel, and should instead be given more expensive drugs. The test’s use is endorsed by the FDA. But a new study, published today in JAMA, found no association between CYP2C19 and cardiovascular side effects in those taking clopidogrel.

Michael Holmes, of University College London, and his colleagues conducted a meta-analysis of 32 studies on the genotype and the drug, totalling 42,016 patients. While there initially appeared to be a relationship, there was evidence it was biased by the small size of studies. When analysis was restricted to larger studies the association disappeared.

“This study identified no clinical significant interaction of CYP2C19 genotype with the association of clopidogrel therapy and cardiovascular events,” write Holmes and his colleagues.

This latest work is in line with a previous meta-analysis – published in the BMJ in August – that also raised questions over the utility of CYP2C19 testing.

In an editorial accompanying the new analysis, Steven Nissen of the Cleveland Clinic in Ohio warns personalised medicine now has a “cult like following” in the media and while it has produced benefits in areas such as breast cancer and has a bright future “overzealous adoption based on limited biochemical data” is not in the public interest.

The FDA estimates the cost of genetic testing to be between $60 and $500 and clopidogrel is used by some 40 million people around the world, according to the JAMA papers.

“The consequences of the FDA’s leap to judgement regarding CYP2C19 cannot be underestimated,” Nissen writes.

See also

Man on a mission (2007 profile of Steven Nissen).

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