Most of us know somebody who has defied a packet-a-day habit to live to a ripe old age. As it is probable that genetic factors help to explain why some smokers avoid lung cancer, it is easy to understand the appeal of the Respiragene test.

The idea that a DNA test can accurately predict risks to a smoker’s health, however, is at best premature and at worst dangerous. Those who take the test in expectation of a licence to enjoy their cigarettes would be well advised to check exactly what they are smoking.

While genetic variations that affect lung cancer risk have been identified, the research is in its infancy. The few genes that have been reliably linked account for only a small fraction of inherited risk, and testing these alone is quite likely to provide a misleading picture. What is more, Respiragene considers many genetic variants that have been linked to lung cancer in cursory fashion. It examines 20 genes, only two of which are used by deCODEme, a rival DNA testing service that includes only variants that are robustly linked to disease.

Even those genes that have been reliably associated may not affect the carcinogenic damage caused by smoking. Rather, they seem to make smokers more likely to become addicted. A gene test may not assess your cancer risk but how easy you will find it to give up.

The Respiragene test, too, looks only at the risk of lung cancer. It tells you nothing about other cancers, heart disease, strokes or emphysema.

Most importantly, however, all smokers have a high risk of lung cancer, whatever their genetic profile.

As Respiragene points out, even those who get the lowest score on its test are almost 20 times more likely to get lung cancer than non-smokers. It is hard to escape the conclusion that £300 would be better invested in nicotine gum.

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