Selective breeding to produce doll-like dogs has resulted in horrific brain problems that researchers are only now just beginning to fully understand.

A new study, published in the latest PLOS One, finds that the brains of some of these dogs have parts that are pushing up against themselves and the dogs’ skulls. The affliction, known as Chiari malformation, could cause the dogs to experience excruciating headaches, problems with walking, and/or paralysis.

“Chiari malformation can be described as trying to fit a big foot into a small shoe,” lead author Clare Rusbridge, from the new School of Veterinary Medicine at the University of Surrey, was quoted as saying in a press release. “It can be very painful, causing headaches and pressure on the brain and can result in fluid filled cavities in the spinal cord.”

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The disease affects many toy dog breeds, such as Griffon Bruxellois (also known as the Brussels Griffon), Cavalier King Charles Spaniels, Chihuahuas and their crosses.

For the study, Rusbridge and her team took brain, skull and vertebrae measurements of 155 Griffon Bruxellois dogs affected by the condition, and compared the data with measurements taken of normal Griffons.

The researchers discovered that Griffons with the disease had taller foreheads. The condition had also caused the shape of the brain to change, with severely affected animals having their cerebellum (the part of the brain at the back of the skull) pushed underneath the main part of the brain.

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A dog with the condition might look cute and doll-like on the exterior but, on the inside, its brain could display this terrible malformation.

The problem may happen all on its own, without breeder involvement. The condition can affect humans, for example, but only when certain skull bones fuse too early, causing parts of the brain to push through an opening in the base of the skull. The disease currently affects 1 in 1,280 humans.

In dogs, some breeders can make the disease more prevalent in their quest to churn out attractive canines with little regard to their long-term health prospects.

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“We want to engage breeders and give them practical advice about the condition, but it is also important that the public recognizes that breeding dogs in a certain way to influence how they look might not be in the animal’s best interest,” Rusbridge said.

She continued, “There are responsible breeders out there, who have invested in screening and who are breeding for health as well as producing attractive puppies, and it is vital that people only look to buy from them.”

Or, adopt from a shelter or other such organization. Many people surrender toy dogs because they cannot properly care for them.

In the future, the researchers hope to develop more sophisticated ways of screening for the disease, so that risk for it can be detected more easily at an earlier age and with a single MRI scan.

(Image: Chihuahua; Wikimedia Commons)