Congenital and Inherited Disorders of Bones, Joints, and Muscles in Dogs
Animals that contract viral infections in the womb may be born with diseased or deformed musculoskeletal systems. Abnormalities may also be congenital (present at birth) if a mother eats toxic plants at certain stages of the pregnancy. Some inherited (genetic) conditions affecting the musculoskeletal system may be neurologic in origin.
Dyschondroplasia in dogs is a hereditary skeletal disorder in which the bones of the limbs or trunk and head may be underdeveloped or deformed. Dyschondroplasia of the limbs is reported in Poodles and Scottish Terriers. The disorder may be seen in the trunk and head of Alaskan Malamutes, Basset Hounds, Dachshunds, Poodles, and Scottish Terriers. Malamutes with dyschondroplasia also have a deficiency of red blood cells (anemia). Among Basset Hounds, Dachshunds, and Pekingese, body characteristics produced by the disorder (short legs with long bodies) are an important feature of the breed type.
Numerous examples of progressive muscle diseases (myopathies) have been described in animals. They may be inherited, and many resemble various types of muscular dystrophy in humans.
Several types of muscular dystrophy are seen in dogs. One type (similar to Duchenne muscular dystrophy in humans) has been seen in Golden Retrievers in the United States and Irish Terriers in Europe. Male dogs are more likely to be affected. Signs include muscular weakening, difficulty swallowing, a stiff gait, and a loss of muscle mass. The disease is caused by the lack of a key protein required for normal functioning of muscle membranes. Some affected dogs have an accompanying heart muscle disease.
A second type of dystrophy affects Labrador Retrievers in North America, Europe, and Australia. Dogs with this type of dystrophy will show a stiff gait; they will resist exercise and begin to lose muscle mass as early as 6 months of age. Bouviers in Europe may develop another type of dystrophy that affects their ability to swallow.
Glycogen is a complex carbohydrate that is normally stored in the liver and muscles. The body converts it to glucose (sugar) as a source of energy. Some animals with glycogen storage diseases progressively weaken until they are unable to rise from a lying position. To date, 5 of 11 types of glycogen storage diseases found in humans have also been found in animals. Affected species include dogs, cats, cattle, sheep, horses, quail, rats, and mice. In particular, Type II glycogenosis has been reported in Lapland dogs.
Hip dysplasia is a common developmental disorder of the hip joints. The femur (the large bone of the upper leg) does not fit properly into the hip socket, which eventually leads to arthritis. An increased risk of the disorder can be inherited in many large breeds of dogs.
Osteochondrosis is most commonly seen in large and giant breeds of dogs. The condition affects bone formation in early stages of life (4-8 months of age), when a dog is growing at its fastest and the stress to the immature skeleton is greatest. In osteochondrosis, the immature joint cartilage may separate from the bone. This detached cartilage is left to float loosely in the joint cavity, where it can cause inflammation, cartilage debris, and further interference with proper bone formation. It most often affects the shoulder, elbow, knee, and tarsal (ankle) joints, in decreasing order of frequency.
Dogs with osteogenesis imperfecta inherit very fragile bones and loose joints. The long bones (such as the major bones of the front and hind legs) tend to be slender with thin outer layers. A veterinarian diagnosing the condition looks for calluses on the bones that indicate recent breaks and fractures. The whites of the eyes of animals with osteogenesis imperfecta may also have a bluish tinge.
A rare disease that appears to be inherited, osteopetrosis has been seen in dogs. Animals with osteopetrosis are stillborn 10 to 30 days before term. The condition produces a shortening of the lower jaw, impacted molar teeth, and easily broken long bones. Bone marrow cavities in the skull as well as the long bones fill with a spongy type of bone instead of marrow. The resultant thickening of the skull compresses the brain.
Several other congenital and inherited musculoskeletal disorders have been seen in dogs. Dogs can be born without feet (apodia) or without certain bones in their limbs (hemimelia). Dogs can also be born with split or missing toes, a condition called "lobster claw" defect or ectrodactyly syndrome. Extra toes (called polydactyly) is far more common and is seen in Great Pyrenees dogs. Finally, a few dogs with toes that are fused together (syndactyly) have been reported.