It turns out the shape of the skull may not be the only reason some short-snouted dog breeds have trouble breathing.

The culprit could be a genetic mutation.

Certain breeds of dogs and cats are prone to difficult, obstructive breathing—a condition called brachycephalic obstructive airway syndrome (BOAS) because of the shape of their head, muzzle, and throat. The most common dogs breeds affected are the brachycephalic breeds such as English and French bulldogs, pugs, and Pekingese.

Because they’re bred to have relatively short muzzles, the throat and breathing passages in these dogs are frequently undersized or flattened.

Scientists had thought their short faces were the only explanation for their breathing problems. However, Norwich terriers, who are not brachycephalic and have proportional noses, suffer from a similar breathing problem: upper airway syndrome.

Scientists at the University of Edinburgh’s Royal School of Veterinary Studies decided to see if there were any other similarities between the Norwich terrier and brachycephalic breeds. In a recent study, the team analyzed DNA from more than 400 Norwich terriers.

The researchers discovered a DNA mutation in a gene called ADAMTS3, which isn’t linked to skull shape but has been linked to edema (fluid retention and swelling).

Because edema may play a role in the breathing difficulties of Norwich terriers, the researchers theorize that fluid retention and swelling in the tissues that line the airways may make it more likely that the ADAMTS3 variant plays a role in the breathing difficulties of other breeds who share the mutation, which is common in French and English bulldogs.

Jeffrey Schoenebeck, PhD, corresponding author of the study, said, “Our study raises the possibility that, rather than being a symptom of airway disease, edema within the [tissues that line the airways] may cause or exacerbate airway disease.”

“Brachycephalic obstructive airway syndrome is . . . a bit of a misnomer,” Schoenebeck added. “Its name suggests that the only thing that causes [the] disease is skull shape. The name ignores the evidence that body condition, size, age, and environment also elevate disease risk.”

And given that, for the first time, there’s evidence that genetic factors like the ADAMTS3 variant can cause airway disease independent of skull shape, Schoenebeck said, “I think upper airway syndrome is a better, less-restrictive descriptor of a large class of respiratory diseases faced by brachycephalic and nonbrachycephalic dogs alike.”

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