Metabolic Disorders Due to Lysomal Enzyme Deficiency in Dogs
Mucopolysaccharidoses are a group of metabolic disorders characterized by the accumulation of GAGs (glycosaminoglycans, or mucopolysaccharides) due to the impaired functions of lysosomal enzymes. It is the mucopolysaccharides which help in building bones, cartilage, skin, tendons, corneas, and the fluid responsible for lubricating joints.
Plott hounds, Labrador retrievers, wire-haired dachunds, Huntaway (sheep) dogs, miniature pinschers, miniature schnauzers, Welsh corgis, mixed breeds, and German shepherds are predisposed to mucopolysaccharidoses.
Symptoms and Types
Symptoms and signs depend upon the type of enzyme deficiency, type of GAG stored, and the tissue in which storage occurs. Some of the more common ones include:
- Severe bone disease
- Degenerative joint disease (DJD), including partial dislocation of hip joint
- Facial structural deformity
- Enlarged liver
- Enlarged tongue
- Eye cloudiness
Mucopolysaccharidoses is a genetic abnormality. However, inbreeding increases the risk, especially if the defective gene is present in the family.
You will need to give a thorough history of your dog’s health, including the onset and nature of the symptoms, to your veterinarian. He or she will then perform a complete physical examination, as well a biochemistry profile, urinalysis, and complete blood count (CBC). These tests may reveal valuable information for initial diagnosis, including the presence of characteristic granules within neutrophils and monocytes (types of white blood cells). Your pet’s veterinarian will also take a sample from other body sites and organs -- such as the liver, bone marrow, joints, and lymph nodes -- for further analysis.
Definitive diagnosis, however, is typically made by measuring the lysosomal enzyme levels in blood or liver. Bone X-rays, meanwhile, will reveal decreased bone density and other bone- and joint-related abnormalities.
If a bone marrow transplant is conducted at an early age, the dog may be able to live a “near normal” life. However, this treatment is expensive, life-threatening, and not very helpful at a mature age. Also, a healthy donor is required for bone marrow transplant.
Enzyme replacement therapy is effective in dogs with mucopolysaccharidoses, but this, too, is an expensive recourse and has not been widely used in animals. Gene therapy, meanwhile, is thought to be an effective method of treatment, and is under evaluation for the treatment both in humans and animals.
Living and Management
Overall prognosis in dogs that have undergone bone marrow transplants is usually good. However, as the dog gets older, it will suffer from various problem, including eating difficulties. Therefore, they will require softer and easily palatable foods. Dogs with mucopolysaccharidoses are also prone to infections and may require antibiotic therapy.
Due to the genetic nature of this group of disorders, your veterinarian will recommend against breeding dogs with mucopolysaccharidoses.