This is an inherited storage disease due to insufficient activity of the enzyme heparan N-sulfatase which is responsible for breaking down heparan sulfate.

Heparan sulfate is an important component of connective tissue.

In affected dogs, there is an accumulation of breakdown products in cells, especially those of the nervous system.

Affected dogs typically present around 18 months of age with neurologic deterioration.

Unlike other forms of mucopolysaccharidoses in dogs, MPS IIIA (New Zealand huntaway type) is a primarily progressive neurologic disease with more limited involvement of the joints and organs.

Symptoms include gait abnormalities and loss of learned behavior.

Disease progression is rapid and affected dogs are often euthanized within a month of the onset of clinical signs.