Mucopolysaccharidosis (MPS) IIIA is an inherited lysosomal storage disorder. Affected dogs have insufficient activity of the enzyme heparan N-sulfatase which is responsible for breaking down heparan sulfate. Heparan sulfate is an important component of tissues throughout the body. In affected dogs, there is an accumulation of breakdown products in cells, especially those of the nervous system. Affected dogs typically present around 3 years of age with neurologic deterioration. Unlike other forms of mucopolysaccharidoses in dogs, MPS IIIA is primarily a progressive neurologic disease with more limited involvement of the joints and organs. Symptoms include ataxia and loss of reflexes more severely affecting the hind limbs, head tremors, swaying, and abnormal eye movement. Although disease progression is slow, affected dogs are often euthanized within a few years of diagnosis.

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