Scientists identify obesity genes shared by humans and dogs

By Stephen Beech

Obesity genes that cause people and dogs to pile on the pounds have been identified.

Researchers studying Labrador retrievers discovered several genes associated with canine obesity.

And the Cambridge University team showed that the genes are also associated with obesity in humans.

The dog gene found to be most strongly associated with obesity in Labradors is called DENND1B.

People also carry the DENND1B gene, and the Cambridge team found that it is also linked with human obesity.

The researchers explained that DENND1B directly affects a brain pathway responsible for regulating the energy balance in the body, called the leptin-melanocortin pathway.

An additional four genes associated with canine obesity, which exert a smaller effect than DENND1B, were also mapped directly onto human genes.

Study joint first author Alyce McClellan, of Cambridge’s Department of Physiology, Development and Neuroscience, said: “These genes are not immediately obvious targets for weight-loss drugs, because they control other key biological processes in the body that should not be interfered with.

"But the results emphasize the importance of fundamental brain pathways in controlling appetite and body weight."

Joint first author Natalie Wallis, of the same department, said: “We found that dogs at high genetic risk of obesity were more interested in food.

“We measured how much dogs pestered their owners for food and whether they were fussy eaters.

"Dogs at high genetic risk of obesity showed signs of having higher appetite, as has also been shown for people at high genetic risk of obesity.”

The study, published in the journal Science, found that owners who strictly controlled their dogs’ diet and exercise managed to prevent even those with high genetic risk from becoming obese - but much more attention and effort was required.

The researchers say that, similarly, people at high genetic risk of developing obesity will not necessarily become obese, if they follow a strict diet and exercise regime - but they are more prone to weight gain.

As with human obesity, no single gene determined whether the dogs were prone to obesity; the net effect of multiple genetic variants determined whether dogs were at high or low risk.

Study leader Dr Eleanor Raffan said: “Studying the dogs showed us something really powerful: owners of slim dogs are not morally superior.

"The same is true of slim people. If you have a high genetic risk of obesity, then when there’s lots of food available you’re prone to overeating and gaining weight unless you put a huge effort into not doing so.

“By studying dogs we could measure their desire for food separately to the control owners exerted over their dog’s diet and exercise.

"In human studies, it’s harder to study how genetically driven appetite requires greater willpower to remain slim, as both are affecting the one person.”

The current human obesity epidemic is mirrored by an obesity epidemic in canines with between 40% and 60% of pet dogs overweight or obese, which can lead to several health issues.

The researchers explained that dogs are a "good model" for studying human obesity as they develop obesity through similar environmental influences as humans.

Dogs within any given breed also have a high degree of genetic similarity, their genes can be more easily linked to disease.

The research team recruited owners with pet dogs in which they measured body fat, scored ‘greediness’, and took a saliva sample for DNA. They then analysed the genetics of each dog.

By comparing the obesity status of the dog to its DNA, they could identify the genes linked to canine obesity.

Dogs carrying the genetic variant most associated with obesity, DENND1B, had around 8% more body fat than those who didn't have it.

The research team then examined whether the genes they identified were relevant to human obesity.

They looked at both large population-based studies, and at groups of patients with severe, early onset obesity where single genetic changes are suspected to cause the weight gain.

The researchers say owners can keep their dogs distracted from constant hunger by spreading out each daily food ration, for example by using puzzle feeders or scattering the food around the garden so it takes longer to eat, or by choosing a more satisfying nutrient composition for their pets.

Dr Raffan added: “This work shows how similar dogs are to humans genetically.

"Studying the dogs meant we had reason to focus on this particular gene, which has led to a big advance in understanding how our own brain controls our eating behaviour and energy use.”