One of the more heartbreaking genetic diseases found in the canine world is a condition known alternatively as chondrodysplasia, achondroplasia or chondrodystrophy. Characterized by crippling deformities and abnormally shaped limbs, the disease causes the cartilage cushioning the joints to become deformed and the bones attached to that cartilage to grow abnormally.

The condition is transmitted through a recessive gene. When two carriers of this recessive gene are bred, the resulting animals frequently are born with the disease. Chondrodysplasia also typically occurs in connection with other serious medical problems, including deafness, dwarfism and abnormally shortened life spans. It has a wide range of severity. For example, in dogs whose front legs are affected, the dog may appear nearly normal, or else have front legs that are only slightly bowed. In extreme cases, however, the animal will be crippled due to severely deformed limbs.

There is no cure for chondrodysplasia. Most animals with mild conditions do not experience any pain or difficulty moving. For those with severe deformities, several types of orthopedic surgeries can be performed, with varying degrees of success. In most cases, the surgery is performed when the dog is about 1 year old and the bones have nearly finished developing.

Since both parents must be carriers in order for the disease to appear, it's critical that anyone planning to breed their dog first check to see if the condition is present in the dog's parents, grandparents or siblings. Many kennel clubs and organizations devoted to specific breeds offer testing and certification to identify carriers and affected animals.

As a genetic disorder, chondrodysplasia was first identified in the 1970s; prior to that it was often misdiagnosed as rickets, a disorder seen in severely malnourished animals and humans. In puppies less than six weeks old, the disease usually is only visible on X-rays. As the dog grows, however, the disease causes increasing deformity in the shape and length of the front legs. Again, some affected dogs may appear nearly normal; others become severely impaired over time.

Chondrodysplasia is one of several types of deformities connected with dwarfism in dogs. Many dogs with this disease also have other serious health problems, including cataracts, cleft palates, kidney and liver problems, seizures and potentially fatal heart problems. The syndrome has been linked to a genetic error in the production of cholesterol in these animals, although the problem isn't yet fully understood. There also is evidence linking it to defects in the animal's pituitary gland.

Short-legged dog breeds such as the Bassett Hound, Bulldog, Corgi and Dachshund are more prone to this ailment. Others that are more susceptible include the: Australian Shepherd, Bull Terrier, German Shepherd, Jack Russell Terrier, Malamute, Poodle and Shar-Pei.