Mucopolysaccharidosis VII (MPS VII) is an extremely rare genetic disorder caused by mutations affecting lysosomal storage. Several different types of mucopolysaccharidoses (MPSs) exist in dogs, humans, rats and other animals, but MPS VII is more common in German shepherd dogs than other breeds.
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Cause
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MPS VII is caused by the deficiency of an enzyme, beta-glucuronidase, which is critical for the development and maintenance of the skeleton and joints. This enzyme is present in cell lysosomes and is vital for the removal and degradation of glycosaminoglycans (GAGs), which are mucopolysaccharides produced by cellular activities. The inactivity of beta-glucuronidase in dogs with MPS VII causes cellular waste products to build up and wreak havoc on the skeleton, joints, and organs. MPS VII is caused by a recessive gene mutation that renders beta-glucuronidase ineffective.
Progression
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MPS VII is evident from birth and is a progressive and debilitating disorder. From birth to three months, bone and joint disease spreads and affects mobility. By three to six months, dogs with MPS VII are unable to stand or move, and muscle tissue begins to waste due to inactivity. Visual impairment due to corneal clouding can also occur, causing limited vision or blindness. By five to 22 months, dogs become lethargic and disinterested as the disease affects the brain.
Diagnosis
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Since MPS VII is evident from birth, the first symptoms occur early in development. After noticing difficulty walking or standing, a licensed veterinarian will perform a physical examination including blood tests and x-rays of the skeleton. Genetic testing is also available, since dogs with MPS VII should not be bred. Blood tests determine the levels of blood enzymes, and DNA tests determine the specific type of MPS disorder afflicting the dog. Skeletal x-rays reveal abnormalities in bone and joint development characteristic of MPS VII. A newly developed urine test can determine the levels of mucopolysaccharides and diagnose all types of MPS disorders.
Breeds Afflicted
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MPS VII was first discovered in a mixed breed dog, but subsequent research performed by Silverstein Dombrowski determined that the German shepherd commonly carries the mutation. Although the mutation may arise in other breeds, no reported cases exist outside of German shepherds and mixed breeds with German shepherd ancestry.
Treatment
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No treatment exists for MPS VII, and German shepherds afflicted are usually euthanized after they lose the ability to walk. Genetic testing is important in dogs used for breeding to prevent this disease from passing to puppies. Since MPS VII is a recessive disorder, German shepherds should be tested even if the dogs show no symptoms of the disease. Dogs that carry the gene responsible may appear healthy, but should be removed from the breeding pool in order to ensure the health and stability of future generations.
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