An obesity gene which could pass from father to child has been discovered by scientists in Paris.

But the majority of people in Europe carry the gene - so it is only one piece in the jigsaw of reasons why obesity develops.

There are thought to be a number of reasons why a child or an adult grows up to be severely overweight.

Being obese as a child greatly increases the chances of obesity in adulthood, and this in turn raises the risk of dangerous medical conditions such as high blood pressure and even cancer.

The number of obese children and adults is on the rise in Western societies - a fact blamed mainly on "couch-potato" lifestyles and fatty diets.

Doctors believe the fact that obesity appears to run in the family suggests there are a number of genes which pre-dispose someone to put on weight.

So far, some genes have been found - but these appear to relate to less common, more severe forms of obesity.

Gene to blame?

The latest gene may, say scientists, may play a far more common role in the development of the condition.

The scientific team focused on the genes involved in controlling the production of the hormone insulin.

It is known insulin plays a key role in the processing of fat in the body - if this process is slowed-down, fat can accumulate and lead to obesity.

The patients examined by the researchers had variations in a particular section of DNA which indirectly exerts some control over insulin production, and the production of an insulin-related growth factor chemical.

Obesity more likely

They found children who had inherited one particular variant from their father were far more likely to be obese.

This variant, called Type I, is more frequent in central European and north African people - perhaps explaining why obesity rates are higher in these places.

But these genes are not the whole answer, the researchers warn.

Their calculations suggest up to two-thirds of all children will inherit this variant - and therefore could be somehow pre-disposed to obesity.

The actual obesity rates are much lower, demonstrating that there must be some additional genes, and external factors such as lifestyle which could affect the outcome.