Dr Christian Jessen: Don't diagnose over the internet

In the film those that did not test genetically "pure" enough formed an underclass of citizens. All the horrors of racism and eugenics we have seen throughout history were distilled into a simple blood test.

The film was a fantasy but the issues it raised are now becoming more and more real. Genetics companies are springing up on their tightly coiled DNA strands offering the public online testing for a host of different inherited genetic disorders and so now the debate rages on whether or not this is appropriate.

As more and more medicine is becoming "defensive" (taking preventative measures aimed at stopping you getting the disease in the first place instead of trying to treat the disease once you have it) genetic testing would appear to fit in with this new philosophy rather nicely. There's no doubting the potential for genetics to help us predict much earlier whether somebody will contract a disease, and so make appropriate life saving interventions earlier.

Some tests allow families to avoid having children with devastating diseases or identify people at high risk for conditions that may be preventable, others help clarify a diagnosis. But these are all tests done by experienced clinicians in a controlled environment with appropriate counselling, and are not an issue.

It's the commercialised online tests on offer for adult-onset disorders such as Alzheimer's disease and some cancers that are the subject of most of the debate over gene testing, and worry me. The tests can only hint at a probability for developing the disorder. Interpretation of the result can be very difficult, as some people who carry a disease-associated mutation never develop the disease.

Nor do we really know what to do once you get your results — the most effective ways to prevent breast or ovarian cancer is still not known, and surgically amputating the breasts and ovaries to lower cancer risk does not necessarily get rid of every cell. It lowers, but does not entirely eliminate risk.

Most importantly of all, normal test results don't guarantee healthy genes. Many women get breast cancer, and many of them will test normal for known breast cancer mutations. Many, many questions are created, few of which can be easily answered. How can Mrs Panic, sitting at home in Middle England hope to understand the results contained in the letter as it drops through the letterbox on a Saturday morning? She can't, and I suggest that it would be her undoing. The physical risks with these genetic tests will be very small, but the emotional, financial and social consequences will be far higher.