British and French scientists have identified several variants of a single gene that boost the risk of obesity, according to a study published Sunday in the British journal Nature.

Previous research had show that an extremely rare mutation in the same PCSKI gene can, all by itself, lead to huge gains in weight, making it the only known source of so-called “monogenetic” obesity.

But a team led by Philippe Froguel of Imperial  College London wanted to find out if PCSKI might lead, in combination with other genetic factors, to more complex and widespread forms of obesity as well.

When they compared the genomes of 13,000 obese individuals of European ancestry to those of a normal control group, the researchers found three mutations in the gene that were far more common among those coping with excess weight.

These same variants were also linked to increased risk of childhood obesity, as well as less extreme weight gain, the study found.

The benchmark for obesity is the body-mass index (BMI), defined as one’s weight in kilograms divided by the square of one’ height in meters.

 A BMI from 18.5 to 25 is considered in the healthy range, from 25 to 30 is over weight and 30 or higher is obese.

PCSKI produces an enzyme, called proconvertase I, that plays a critical role in converting inactive forms of hormones that control appetite and regulate energy metabolism into active forms.

These hormones include insulin and glucagons, involved in the metabolism of sugar and carbohydrates, as well as a third molecule that signals to the brain that one has eaten enough.

“Nearly 25 per cent of the population (studied) has a different form of the enzyme that is apparently a little bit more active,” Froguel told AFP in an interview.

            The study began with 150 families who responded to a public appeal to participate in research on obesity has at least one obese child.

The researchers then expanded to a larger population in France, as well as new cohorts in Denmark, Switzer land and Germany.

Obesity and obesity-related diseases such as diabetes have gained epidemic proportions in many developed economies.