Scientists Uncover The Genetics Behind A Pug’s Unique Mug

The same mutations could help explain why pugs and people have facial deformities

A pug competes during the 5th southern Germany pug and bulldog race held last September — Christoph Schmidt/Getty Images
May 30, 2017 at 1:53 PM ET

To look into a pug’s permanently wrinkled face, adorned by its bugged out, glassy eyes, is to see a beautiful sort of tragedy. A pug’s purposefully bred smushy face and curly, cinnamon roll-like tail may make it the stuff of Instagram celebrity, but these traits are also an indicator of severe health risks.

Pugs and other breeds like them, such as boxers and bulldogs, are known as brachycephalic dogs, which references their short and broad skulls. These skulls unfortunately doom many to a lifetime of health problems, like trouble breathing, frequent eye injuries, and sleep apnea. They’re also more likely to be born with deformed spines that can cause neurological issues. Their fate is so beleaguered that a growing number of veterinarians are telling people to stop buying them.

Now, thanks to a new study published earlier this May in Current Biology, we might have a genetic clue as to why these dogs look like the way they do. And that discovery could have big implications for both dogs and people.

Researchers collected the imaging tests of nearly 400 dogs’ skulls that had been taken at a veterinary clinic. The scans, taken of both purebreds and mixed breeds, were then used to create 3D models that allowed researchers to pinpoint subtle skull shape variations between and within different breeds. Finally, they cross-referenced these skull models with the dogs’ entire genetic structures, or genomes.

As expected, extremely brachycephalic breeds, like the pug, were the most likely to have stout faces. And they found a grouping of genes seemingly linked to facial length. Likely due to genetic variations involving this region of the chromosome, pug-like dogs expressed less of a gene called SMOC2, which is known to help cells adhere to one another and heal wounds. Scientists elsewhere have also found evidence that this gene helps maintain normal facial development across a variety of species, including people.

The varying levels of SMOC2 expression only accounted for about a third of dogs’ facial length, the researchers noted. And they didn’t explain a few other smush-faced breeds, like the Affenpinscher, aka the monkey terrier. But the researchers are hopeful their cranial skull project, which they intend to expand, will eventually uncover the exact role SMOC2 and other genes are playing in shaping these dogs’ faces. That could then explain why some people have similar facial deformities.

“Leveraging the craniofacial diversity of dogs, we set out to discover candidate genes involved in human craniofacial anomalies,” the authors wrote. “Our results suggest that SMOC2 should be screened as a candidate for diagnosis.”