Dachshunds and Basset Hounds may look cute as they scurry around on their short legs, but the familiar shape of these short-legged breeds is actually due to a congenital defect that results in a form of dwarfism. Specifically these animals have achondroplasia, an improper development of the cartilage at the end of the animal's long bones. It's a defect that can occur in any breed of dog, and is always present in certain breeds like the two mentioned above.
Achondroplasia is one of several types of chondodystrophies, in which the cartilage does not develop properly in the womb, distorting the animal's bones. A dominant genetic defect, achondroplasia appears in about one out of every 10,000 births, and can usually be diagnosed at birth, since the deformities are easily visible. Any dog with the defective gene will be affected, and if the dog is bred, its offspring have a 50 percent chance of being achondroplasic.
Further, many dogs with achondroplasia and other chondodystrophies often have 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.
In normal animals, the body deposits calcium within cartilage, which is a fibrous connective tissue. Over time this calcium-enriched cartilage hardens and turns into bone. In achondroplasia, these bones do not grow as long as they should, and they also become abnormally thickened. It's usually just the legs that are affected. However, in many cases the opening in the skull through which the spinal cord passes (the foramen magnum) is narrower than normal. Also, the openings in the vertebrae through which the spinal cord runs also can be abnormally small. Both of these malformations make these animals vulnerable to paralysis if the spinal cord is compressed or injured.
Achondroplasia frequently occurs in conjunction with other serious medical problems, including deafness and abnormally shortened life spans. It has a wide range of severity. In some cases the animal's legs may appear nearly normal or only slightly bowed; in extreme cases, the animal will be crippled due to severely deformed limbs.

There is no cure for achondroplasia and its related chondodystrophies. 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 achondroplasia is a genetically inherited disorder, 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. In breeds that are automatically achondroplasic, such as Bassets and Dachshunds, owners should check with their veterinarian about any breeding or health concerns.