Mucopolysaccharidosis IIIB, Sanfilippo Syndrome Type B, MPS IIIB


The mucopolysaccharidoses (MPS) are a group of hereditary lysosomal storage disorders in which specific glycosaminoglycans (GAGs) accumulate in lysosomes. Mucopolysaccharidosis III is characterized by lysosomal accumulation of the GAG heparan sulphate (HS). Unlike other forms of MPS, MPS III causes a progressive and primarily neurological disease.

  • Signs and symptoms

    Affected dogs develop a slowly progressive ataxia, typically leading to humane euthanasia before six years of age. Other signs include mental dullness, with exaggerated abnormal gait (hypermetria), truncal swaying (pulling the spine and attached tissues back and forth), and fine whole-body and head tremors.

    Clinical signs may be observed at approximately two years of age.

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  • Diagnosis

    Diagnosis is made based on clinical history, physical examination, genetic testing, and ruling out other causes of similar symptoms. Intracytoplasmic granules may be found in the white cells of peripheral blood and cerebrospinal fluid (CSF), and increased HS may be measured in plasma, CSF, and urine of affected dogs.

  • Treatment

    There is no cure for MPS IIIB; all currently available treatments are symptomatic or supportive in nature. Gene therapy and enzyme replacement therapy are evolving fields that require more research to be available clinically.

  • What to do if your dog is at risk


    • Please give your dog any medication as prescribed by your veterinarian.
    • Keeping your affected dog comfortable at home is the best therapy you can provide.
    • Slings can be used to assist with their mobility, and caution should be taken to avoid falling hazards.

  • Genetic Information

    Since the discovery of the causative variant, selective screening and breeding practices have led to a dramatic decrease in allele frequency within the Schipperke breed.

    Mucopolysaccharidosis IIIB is recessive, that is, a dog requires two copies of the variant to show signs of the disease from the variant. This variant was first described in Schipperke.

    Gene names:

    NAGLU ‐ chr9

    Inheritance type:


  • Breeds affected

    This health condition affects the following breeds

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