A SALISBURY grammar school "old boy" led a team of scientists hailed for discovering a rogue gene which could be partly responsible for the current obesity epidemic.

Professor Andrew Hattersley, from the Peninsula Medical School at the University of Exeter, headed the team of geneticists with Prof Mark McCarthy, of Oxford University.

And it is hoped the discovery will spawn treatments to help people lose excess weight.

Prof Hattersley was brought up in Salisbury and attended Bishop Wordsworth's School.

His mother, Robina, still lives in the city and his doctor father, Tym, who now lives in Norfolk, was a Salisbury GP and served as Mayor of the city in 1976 and later as chairman of the district council.

Prof Hattersley's great-grandfather was Bishop Wordsworth, the Bishop of Salisbury, who founded BWS.

The team of 42 scientists spent 15 years analysing the DNA and health of more than 40,000 adults and children before pinpointing a gene called FTO.

They found if people carry one copy of a variant of the FTO gene, as does half of the population, it will lead to a gain in weight of two to six pounds or put just over half an inch on their waists and raise their risk of being obese by one third.

If people have two copies of this variant, which one in six of the population do, they will gain almost seven pounds more than those who lack the variation, and are at a 70 per cent higher risk of obesity.

When scientists understand more about the function of this first obesity susceptibility gene, they will be able to help people to lose weight more effectively despite their genes.

This may be achieved with drugs targeted at the molecular pathways the gene influences.

Obesity is a major cause of disease, associated with an increased risk of type 2 diabetes, heart disease and cancer.

It is typically measured using body mass index (BMI). As a result of reduced physical activity and increased food consumption, the prevalence of obesity is increasing.

According to the 2001 Health Survey for England, more than a fifth of males and a similar proportion of females aged 16 and over in England were classified as obese. Half of men and a third of women were classified as overweight.

Prof Hattersley said: "As a nation, we are eating more but doing less exercise, and so the average weight is increasing. But within the population, some people seem to put on more weight than others.

"Our findings suggest a possible answer to someone who might ask: I eat the same and do as much exercise as my friend next door, so why am I fatter?' There is clearly a genetic component to obesity."

His team's research was carried out as part of a major study of diseases, funded by the Wellcome Trust, the UK's largest medical research charity.

Prof Hattersley's mother, who lives at Mill Race, Salisbury, said: "Andrew is all about helping people with diabetes, and those likely to get diabetes. I am very proud of him."