Backstroking through life's gene pool

Your chances of getting back pain are largely determined by your genes, medical researchers said last week. Which, although backed up by reasonable science, seems somewhat surprising. It's hard to find anyone who has had kids (and lugged them round supermarkets) who doesn't complain of backache. If your predisposition for back pain is written in the DNA, then it must be sprinkled liberally throughout our gene pool.

The research, published in the journal Arthritis And Rheumatism, comes from a study that compared the incidence of back pain between identical and non-identical twins. Researchers found that out of the 400 female pairs they studied, the risk of developing disc degeneration in the neck or lower spine due to osteoarthritis (the kind due to wear and tear, as opposed to rheumatoid arthritis, thought to be caused by an immune system fault) was much more common in identical twins. Although spoilsports may say that identical twins have identical bodies and are likely to wear them out in similar places, the study did try to take into account weight, height, smoking, manual work and exercise, all of which affect the risk of wearing out discs.

But if, as the researchers from St Thomas' Hospital Twin Research Unit conclude, genes are responsible for up to 60 per cent of disc degeneration, where does this leave us? Are those of us without the relevant genes (and no one knows which ones they are, although they'll produce proteins because that's what the discs are made of) free to lift heavy objects without bending our knees because, hey, back pain just isn't part of our genetic make-up?

When I was at medical school, it was actually pretty straightforward. Gene X caused disease X. There were few tests that women could have while pregnant to determine if they had a child with a particular genetically inherited disease.

These days, some media reports would have you believe that personality traits, sexual orientation and all sorts of cancers and heart problems are writ large on our personal genetic blueprint. And that one day soon we will have our genes mapped out and know whether it's safe for us to smoke, eat fat or roast ourselves under the sun.

Well, science being science, it'll be murkier than that. Initially the major advances were in finding single genes that caused single diseases, but it rapidly became apparent that genes aren't that simple.

In an editorial in the British Medical Journal, Professor Joseph Alper, a geneticist from the University of Massachusetts, Boston, argues that there may be no such thing as a simple genetic disease. Huntington's disease, a cruel inherited disorder that appears in adult life, causing early death, is caused by three abnormal proteins repeated in a set sequence in the affected gene. When the sequence is repeated only about 30 times, the person may be completely healthy. Yet 10 years ago geneticists firmly believed that any of these abnormal proteins meant certain disease.

A genetic predisposition for a disease may mean no more than any other risk factor for ill-health, such as high cholesterol levels or smoking. Rather than looking at your family wracked by heart disease, and assuming it's genetic and you're doomed anyway, you should think that it's even more important to eliminate other risk factors.

While we repeatedly fail to heed the mass health-promotion messages of stop smoking and eat fruit and veg, people may be more motivated if they think their risk of getting a disease such as bowel cancer is higher than average.

In Denmark, there's a register of people with a1 antitrypsin deficiency, a genetically inherited condition that among smokers causes severe emphysema. The only certain way to avoid the lung disease is to not smoke. If you have the gene for the deficiency and you smoke, you're likely to die at 50 from lung disease. If you don't smoke, you have a normal life expectancy. A study found that 67 per cent of people who knew they had the gene stopped smoking.

Increasingly, the genes being discovered will be those that interact with the environment to cause disease, rather than inflict it on their own. If anything, we should feel positive about the reams of unravelling information that may explain why Aunt Ethel could smoke 40 fags a day and live until the age of 104. But it may not be easy. In my family we've had a bit of dementia, heart disease and, in the past, much backache. When my genetic blueprint comes out, I may ask to read an abridged version.

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