What Is Hunter Syndrome in Dogs?

Hunter syndrome, formally known as mucopolysaccharidose disorder, is a genetic abnormality occurring in canines and humans. It's a metabolic storage disorder resulting in lysosomal enzyme deficiency, which affects nearly every system in the dog's body. Also known as Sly syndrome, Hunter syndrome usually is evident in puppies by the time they reach the age of 1 month. Unfortunately, their condition continues to deteriorate as they grow. Inbreeding can predispose a dog to Hunter syndrome.

Hunter syndrome results from enzyme deficiency. The mucopolysaccharides, which aid in bone formation, as well as that of the skin, cornea and cartilage, don't perform their function properly because of a lack of lysosomal enzymes. These enzymes ensure that chemical reactions in the body proceed at the correct rate. When they're deficient, cells don't work as they should. Your veterinarian can diagnose Hunter syndrome by performing a physical examination, along with blood tests, urinalysis and measuring your dog's lysosomal enzyme levels in his liver. Your vet also may conduct skeletal X-rays to determine the degree of bone abnormalities.

While any canine might be born with Hunter syndrome, it appears more often in certain breeds. These include the Labrador retriever, the Plott hound, the Rottweiler, the miniature poodle, the German shepherd, the miniature pinscher, the Boston terrier, the Welsh corgi, the Chesapeake Bay retriever, the miniature schnauzer and the wire-haired dachshund.

In severely affected dogs, signs of Hunter syndrome are obvious. Some puppies are born with an abnormally large forehead and broad mandible. Dogs generally have bowed rear legs and exhibit lameness or difficulty walking. Other signs include heart murmurs, chronic diarrhea, respiratory issues, skeletal deformities, liver and spleen enlargement, vision problems, enlarged tongue, degenerative joint disease and developmental delays. Dwarf dogs often suffer from Hunter syndrome.

The prognosis for dogs suffering from Hunter syndrome isn't good. Most die fairly young or are euthanized because of severe deformities and poor quality of life. In mildly affected dogs, early treatment with a bone marrow transplant offers some promise, but the procedure is risky, expensive and requires a suitable bone marrow match. In the future, gene therapy might offer help for dogs born with Hunter syndrome. (ref 1)For obvious reasons, dogs with Hunter syndrome or related deformities should not be bred.