Common Symptoms
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 2 years of age with neurologic deterioration. Unlike other forms of mucopolysaccharidoses in dogs, MPS IIIB 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.
Testing Tips
Genetic testing of the NAGLU gene will reliably determine whether a dog is a genetic Carrier of mucopolysaccharidosis IIIB (Schipperke type). This disease is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the NAGLU gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
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Raj K, Ellinwood NM, Giger U. An exonic insertion in the NAGLU gene causing Mucopolysaccharidosis IIIB in Schipperke dogs. Sci Rep. 2020 Feb 21;10(1):3170. doi: 10.1038/s41598-020-60121-3.
[PubMed: 32081995]
