Scientists have discovered among a group of very elderly Jews that their longevity could be due to a mutant enzyme which stops cells ageing. Researchers at the Albert Einstein School of Medicine in the USA studied 86 Ashkenazi Jews with an average age of 97, as well as 175 of their children, and 93 'control' patients whose parents had had an average lifespan.

The centenarians and their offspring were found to all possess high levels of telomerase - an enzyme that replenishes the cells' telomeres, which are short DNA repeat sequences founds at the end of chromosomes. The telomeres protect DNA in the same way that plastic caps protect the ends of shoelaces, by stopping them from 'fraying'.

'Our findings suggest that telomere length and variants of telomerase genes combine to help people live very long lives, perhaps by protecting them from the diseases of old age', said Yousin Suh, lead author of the study, and associate professor of medicine and genetics at the Albert Einstein School. 'It may be possible to develop drugs that mimic the telomerase that our centenarians have been blessed with',' Suh said.

The research is published in the Proceedings of the National Academy of Sciences, and involves this particular Ashkenazi Jewish community because they are a genetically isolated population, so it is easier to identify diseases causing genetic differences.

Compared with the control group, the centenarians had significantly higher levels of telomerase and significantly longer telomeres in their blood samples. Each time a cell divides, its telomeres usually shorten until they reach a critically short length and the cell dies, but people with more active telomeres are may be able to maintain their telomere length and thus prolong the lifespan of their body's cells.

Some experts have cast doubt on the generalisation of the research however. Professor Tim Spector from Kings College London, who carries out research on telomeres and ageing, believes that the findings may not apply to other populations. In addition he said: 'There may be a downside to the plan of boosting the repair processes of DNA because giving the cells more chances to divide may increase the chances of damaging mutations developing and causing cancer'.

The full importance of the role of telomeres was recognised this year when three scientists won the 2009 Nobel Prize in Physiology and Medicine for determining the structure of telomeres and discovering how they protect chromosomes from degrading.