British and French scientists have discovered several variants of a single gene linked to obesity, according to a study in Sunday's journal Nature.

Previous studies have shown that an extremely rare mutation in the same PCSK1 gene can lead to huge gains in weight.

In an effort to find if PCSK1 might lead to more complex and widespread forms of obesity, a team led by Philippe Froguel of Imperial College London compared the genomes of 13,000 obese individuals to those of a normal control group.

The team found three mutations in the gene that were far more common among those coping with excess weight.

PCSK1 produces an enzyme, called proconvertase 1, 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 glucagon, involved in the metabolism of sugar and carbohydrates, as well as a third molecule that signals to the brain that one has eaten enough.

The study found nearly 25 percent of the population (studied) has a different form of the enzyme that is apparently a little bit more active.

Obesity and obesity-related diseases such as diabetes have been increasing in many developed countries. The causes are complex, and include sedentary lifestyle along with eating fat and sugary foods.

But a series of recent discoveries have shown that genetics can also play a bigger role than previously thought.

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

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

(Agencies via Xinhua News Agency July 7, 2008)