Mucopolysaccharidoses in Dogs

Mucopolysaccharidoses are a rare group of genetic disorders that cause physical deformities and organ dysfunction in dogs. The disease is difficult, at best, to treat. There is no cure for Mucopolysaccharidoses, but there are treatments available that have shown some success in younger dogs.

Symptoms vary widely between the different types of Mucopolysaccharidoses. The most common systems can include:

• Slow growth
• Unusually broad chest
• Large head
• Dwarfism
• Corneal clouding and/or ocular lesions
• Weakness in the hind legs and/or deformed legs
• Enlarged liver
• Tracheal dysplasia
• Congestive heart failure

Types

There are four distinct types of Mucopolysaccharidoses, each caused by a deficiency of a different enzyme.

• Mucopolysaccharidosis I: Affects Rottweilers, Boston Terriers and Plott Hounds, and is caused by a deficiency in L-iduronidase.
• Mucopolysaccharidosis IIIa: Finds dogs deficient in N-sulfoglucosamine sulfohydrolase.
• Mucopolysaccharidosis VI: Affects Huntaways, Miniature Poodles, Miniature Pinschers, Miniature Schnauzers, Chesapeake Bay Retrievers and Welsh Corgis. Dogs with this variation are deficient in arylsulfatase B.
• Mucopolysaccharidosis VII: Often called Sly Syndrome, this condition is characterized by a deficiency in B-glucuronidase. It affects Brazilian Terriers, German Shepherds, and mixed breed dogs.

Mucopolysaccharidoses are considered a genetic abnormality. If the gene is present within a family of dogs, inbreeding can increase the likelihood of development in future litters. It is therefore recommended that breeding ceases in a line of dogs once the recessive gene is discovered through DNA testing.

Dogs with Mucopolysaccharidoses are usually diagnosed between two and five months of age, though progressive symptoms are generally apparent in the first month of life.

Your veterinarian will want to observe your dog first, noting any weakness, eye clouding, and skeletal abnormalities. You will also be asked to identify any unusual behavior in the dog you’ve noted at home. Suspicion of Mucopolysaccharidoses may lead to the following tests:

• Urinalysis
• Complete blood count
• Tissue samples
• DNA test
• Lymph node biopsy

High lysosomal enzyme levels present in the blood, urine or the liver, along with a positive DNA test, is considered the hallmark for making a diagnosis of Mucopolysaccharidoses. Bone X-rays and other radiographs are used to confirm joint and bone abnormalities.

There is no cure for Mucopolysaccharidoses. Dogs with this disease can survive with medical and physical assistance for several years though their quality of life is considered to be poor and they are therefore normally euthanized upon diagnosis. Bone marrow transplants, if performed early in the disease, can return dogs to a near-normal state of health.

Intravenous Enzyme Replacement Therapy (ERT) is the standard treatment for young adult dogs, and intrathecal ERT is used to treat dogs between four and 12 months of age. The treatment is helpful in reducing pain and non-neurological symptoms but is costly.

Gene therapy is currently being tested as a probable treatment for Mucopolysaccharidoses but is not available publicly at this time.

Dogs who undergo a bone marrow transplant in puppyhood can live a relatively normal life. Following a transplant, your dog will remain in isolation for 10 days while their body adapts and their white blood cell count rises and reaches a safe level. Human visitors are more than welcome to visit during this time. Dogs are generally allowed to return home after two weeks, provided they’ve stabilized, but will need periodic blood tests for three to four months following the procedure to watch for any signs of infection or complications.