London, May 17 (IANS) A group of scientists claimed to have decoded the gene which is responsible for ageing, a breakthrough which would help develop a drug to enable people live a healthy life for over 100 years.

The lucky carriers of "Methuselah" genes have a much improved chance of living to 100 even if they indulge in an unhealthy lifestyle, timesonline.co.uk reported.

The genes appear to protect people against the effects of smoking and bad diet and can also delay the onset of age-related illnesses such as cancer and heart disease by up to three decades.

No single gene is a guaranteed fountain of youth. Instead, the secret of longevity probably lies in having the right "suite" of genes, according to new studies of centenarians and their families. Such combinations are extremely rare - only one person in 10,000 reaches the age of 100.

The genes found so far each appear to give a little extra protection against the diseases related to old age. Centenarians appear to have a high chance of having several such genes embedded in their DNA.

"Long-lived people do not have fewer disease genes or ageing genes," said Eline Slagboom of Leiden University, who is leading a study into 3,500 Dutch nonagenarians. "Instead they have other genes that stop those disease genes from being switched on. Longevity is strongly genetic and inherited".

Slagboom and her colleagues recently published studies showing how the physiology of people in long-lived families differs from normal people.

"People who live to a great age metabolise fats and glucose differently, their skin ages more slowly and they have lower prevalence of heart disease, diabetes and hypertension," she said.

"These factors are all under strong genetic control, so we see the same features in the children of very old people."

The Methuselah genes - named after the biblical patriarch who lived to 969 - are thought to include ADIPOQ, which is found in about 10 percent of young people but in nearly 30 percent of people living past 100. The CETP gene and the ApoC3 gene are found in 10 percent of young people, but in about 20 percent of centenarians.

The studies show that tiny mutations in the make-up of particular genes can sharply increase a person's lifespan.

Dr David Gems, a longevity researcher at University College London, believes that treatments to slow ageing will become widespread.

"If we know which genes control longevity then we can find out what proteins they make and then target them with drugs. That makes it possible to slow down ageing. We need to reclassify it as a disease rather than as a benign, natural process," he said.