Of the hundreds of dog breeds in the world, experts say only about 18 have ever been reported with sex reversal. But researchers in Spain this week said they can add a new breed to to the list: the French Bulldog.
According to CEU-Cardenal Herrera University in Valencia, specialists discovered that a "female" French Bulldog, Tana, actually had the internal organs of a male during the three-month-old puppy's first visit to the veterinarian. Alerted by an enlarged clitoris, they conducted a series of tests and discovered that "she" had cryptorchid (or undescended) testicles.
"She was a chromosomally XX female but with masculine gonads (cryptorchid testicles) due to the presence of other genes that determined the formation of testicles in the absence of the genes present on the Y chromosome," said Marcos Campos, a researcher at the university.
A study on Tana, of which Campos is the lead author, has been published in the journal Reproduction in Domestic Animals.
Campos did not immediately respond to requests for comment from ABCNews.com, but in a news release said that while hermaphrodites (and pseudo-hermaphrodites) have been identified in other species, such as goats, pigs, horses and humans, and in 18 other breeds of dogs, Tana was the first French bulldog reported with the alteration.
To prevent Tana from experiencing any long-term problems, the specialists surgically sterilized her and completely removed her genitals.
"The puppy is now in perfect health," Campos said.
While hermaphrodite dogs may be rare, they may be more common than most people think.
"There's a difference between what's reported and what actually occurs," said Dr. Kit Kampschmidt, a Houston veterinarian.
While hard numbers on the frequency of sex-reversed canines are difficult to come by, he said his practice sees about one case a year, although he added that his office may see more cases than the average veterinarian because they focus on reproduction.
Kampschmidt said that given how many dogs are spayed and neutered, it's possible that veterinarians are removing the animals' reproductive organs before they have a chance to fully develop, normally or abnormally. Others may encounter hermaphrodite dogs but choose not to publish or officially document the observation.
"This is the first French bulldog reported in the literature, but as with anything, there may have been others that occurred, but were just taken care of by a vet and not published," he said.
Hermaphrodite dogs like Tana are surgically sterilized, he said, but though they may suffer long-term complications like infections and tumors, they could probably live normal lives even without surgery. The motivation to operate, is usually cosmetic or aesthetic, he said.
Other breeds that are known to have some genetic propensity to sex-reversal are Beagles, Chinese Pugs, Kerry Blue Terriers, Weimaraners and German Shorthaired Pointers, he said.
"It's important that these things be published so that we know what types of breeds to look for," said Dr. Kampschmidt. "I think it could spring up in any breed."