As many as one in four Britons have a much-reduced risk of developing alcohol-related cancer thanks to their genetic make-up, scientists have discovered. Researchers have identified two genes that quickly flush alcohol out of the system, thus reducing its carcinogenic effect. People carrying one or both of the genes may have only half the chance of developing mouth, throat and oesophageal cancers that are strongly associated with drinking.
The genes involved are rare versions of ADH7 and ADH1B. The ADH range of genes help the body to process alcohol. Everyone carries two versions of each of these genes, one inherited from each parent, but only 15 to 20 per cent of the UK population have ADH7, while around another 5 per cent have ADH1B.
A study of 9,000 people has shown for the first time that people carrying one or both of these rare gene variants have a much lower risk of getting head or neck cancer than those who have the common versions. For example, those with ADH1B have only half the chance of developing such cancers and people with ADH7 are at a 32 per cent reduced risk.
Researchers say the findings are significant because it is the first time they have pinned down genes that have a protective effect against alcohol. 'We don't know how the protection occurs, but we do now know that these genes have that effect, and that could be hugely useful in giving us a much broader understanding of cancer processes in general,' said Professor Martin Wiseman, medical and scientific adviser to the World Cancer Research Fund, which helped to fund the study.
Alcohol is one of the major causes of cancer, along with smoking and diet. It is estimated to be responsible for about 5 per cent of the 285,000 new cases of cancer diagnosed every year. Experts say convincing evidence shows that it is linked to cancers of the mouth, breast, bowel, liver, pharynx, larynx and oesophagus.
Health experts welcomed the findings, but warned that they should not be interpreted as a green light to drink heavily. 'This shouldn't have any direct effect on people's drinking behaviour. Those people with one or both of these rare gene variants are lucky in that they are at lesser risk of developing these cancers. Having up to half the risk is significant,' said Wiseman. 'But they still face some risk. So the advice to them wouldn't be, "Go away and drink". It would be, "For cancer prevention, avoid alcohol entirely if you can and, if you do drink, limit it to one drink a day for a woman and two drinks a day for a man".'
Those who carry such genes would not know it, as a family doctor cannot tell and there is no reliable test to tell someone their genetic make-up that can be easily accessed, Wiseman added.
Dr Paul Brennan, the researcher who led the study at the International Agency for Research on Cancer in France, said: 'Every human being has the seven [ADH] genes that, when you drink a beer or whisky, start to break down the ethanol in the alcohol which many believe is the cancer-causing agent. But those 20 to 25 per cent of people who have one or both are gene variants - if they drink alcohol, their risk of getting these head and neck cancers is reduced by about half.'
The discovery made by Brennan and his team is outlined in a paper published in the journal Nature Genetics. They found that 20.5 per cent of people in Manchester, 16 per cent in Edinburgh and 15 per cent in Newcastle carry the rare variant of ADH7, while 6 per cent of people in the Scottish capital and 4 per cent of those in both English cities have the uncommon form of ADH1B.
Now that the two genes have been identified, scientists will start to examine how the proteins they produce assist the body by aiding the natural process of cleansing toxins. This has long-term potential to help in the development of drugs that might mitigate the damaging effects of alcohol consumption.
While the study is good news for up to a quarter of the population, it also provides further evidence of how drinking even moderate amounts of alcohol can increase the risk of getting cancer.
Dr Julie Sharp, science information manager at Cancer Research UK, said: 'This adds to existing evidence that alcohol increases the risk of these types of cancer. It also highlights that both our genes and our lifestyle influence cancer risk and will help scientists understand more about the disease.'
However, Sharp added: 'It's important to stress that these results don't mean that people can drink too much and hope they won't be at risk. These genetic variants are rare and still don't protect people totally from the damage caused by alcohol.'
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