New research is finding that Chiari malformation is on the rise among toy dog breeds. Some of the most commonly affected breeds include those who are specifically bred to have doll-like or apple shaped heads, such as Chihuahuas, Griffons Bruxellois and even Cavalier King Charles Spaniels. A study from the University of Surrey has uncovered some of the problems that Chiari malformation causes among these breeds.

In humans, Chiari malformation occurs when seams in the bones of the skull fuse too quickly in young patients. This causes pressure that pushes parts of the brain through the base of the skull. While many toy dogs with Chiari malformation show no symptoms, others can have severe problems. The increased pressure can cause headaches and push spinal fluid into pockets along the spinal cord. In serious cases, affected dogs can have poor motor function or even paralysis.

Experts say that the soaring number of Chiari malformation among toy breeds is the result of selective breeding. Scientists measured the skull and spine of 155 Griffons. As they compared the measurements, it became clear that dogs and puppies with exceptionally tall foreheads were at much higher risk for this condition.

By purchasing puppies from reputable breeders with responsible breeding programs and veterinary supervised health programs, future pet owners can help to reduce the number of dogs with Chiari malformation. Dr. Clare Rusbridge from the University of Surrey warns that breeding dogs for specific traits isn’t always beneficial to the breed.

Meanwhile, researchers from the University of Surrey have teamed up with geneticists from the University of Montreal. With as many as one in 1280 humans affected by this disease, the hope is that they can find better ways to treat this condition in both humans and dogs.