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Here's Why Brachycephalic Dogs Such As Pugs And Bulldogs Have Flat Face

Study of dog DNA has unveiled the genetic mutation associated with flat face shapes that are seen in pugs and bulldogs.

Selective Breeding

Researchers have long known that dogs characterized by flat faces are the result of selective breeding. The pug, for instance, was selectively bred so it will feature an extremely flat face.

Scientists, however, have not yet discovered the exact DNA roots behind the physical traits of these flat-faced canines. New DNA analysis now get them closer to finding the genetic mutation responsible for the distinct flat face of some dogs.

Genetic Mutation Behind Brachycephaly In Dogs

For the new study, researchers at the University of Edinburgh's Roslin Institute conducted an analysis of DNA samples taken from 374 pet dogs of different pedigree and breeds.

Three-dimensional images of the dogs' heads from CT scans allowed the researchers to get the precise measurements of the dogs' skull. By comparing the measurements of the skulls and the dog's genetic information, the researchers were able to identify DNA variations linked to different head shapes.

One variation that was found to disrupt the activity of the gene called SMOC2 have a strong association with the length of the dogs' faces. The gene encodes a protein that helps cells stick to things, multiply, and rebuild the tissues. In some animals such as fish and mice, it plays an important role in facial development.

The researchers found that the animals with the SMOC2 mutation tend to have significantly flatter faces, a condition known as brachycephaly. The more the mutation was able to suppress the gene, the flatter the faces of dogs.

"SMOC2 disruption affects the facial skeleton in a dose-dependent manner. The size effects of the associated SMOC2 haplotype are profound, accounting for 36% of facial length variation in the dogs we tested," the researchers wrote in their study, which was published in the journal Current Biology on May 25.

Health Woes Of Brachycephalic Dogs

The researchers said that the findings have implication in human and veterinary medicines. Some human babies are also born with brachycephaly albeit little is known about the cause.

Dogs with flat face are also known to be prone to certain conditions, prompting some veterinarians to warn pet owners about owning flat faced-dogs.

Smooshed-face dogs, or the brachycephalic dogs, such as pugs and Boston terrier, boxer, bulldog, Pekingese, and Shi Tzu, may appear cute, but their facial characteristics marked by wide face and bug eyes are not favorable for their health.

These animals, for instance, are known to frequently suffer from digestive respiratory distress. They are also more likely to get more eye injuries compared to other dogs. A new study has also showed the pugs and bulldogs have higher risk of suffering from heatstroke because of their flat face. Veterinarians said that their flat face makes it difficult for these brachycephalic dogs to cool down.

"Our results shed light on the molecular nature of this type of skull form that is so common and popular among dogs," said study researcher Jeffrey Schoenebeck.

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