Mucopolysaccharidosis (MPS) VII (Brazilian terrier type) is an inherited Lysosomal Storage Disorder affecting dogs. Affected dogs have insufficient activity of the Enzyme beta-glucuronidase, which is responsible for breaking down glycosaminoglycans (GAGs). GAGs are an important component of Connective Tissue. In affected dogs there is an accumulation of breakdown products in cells causing abnormal growth and function of various different organ systems. Clinical signs of MPS VII (Brazilian terrier type) are most commonly associated with accumulations in the bones and joints. Therefore, affected dogs typically present between 1 to 4 weeks of age with symptoms of bone and joint disease. Affected puppies have disproportionally large heads with short muzzles, broad faces and domed skulls. Other skeletal deformities include joint laxity and deformed, crooked legs resulting in an inability to walk. Affected puppies are smaller than their normal littermates and exhibit a failure to thrive. Affected dogs die on their own or are euthanized within the first 5 weeks of life.
Genetic testing of the GUSB gene will reliably determine whether a dog is a genetic Carrier of mucopolysaccharidosis VII (Brazilian terrier type). Mucopolysaccharidosis VII (Brazilian terrier type) 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 GUSB gene mutation. Reliable genetic testing is important for determining breeding practices. 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.
Hytonen MK, Arumilli M, Lappalainen AK, Kallio H, Snellman M, Sainio K, Lohi H. A novel GUSB mutation in Brazilian terriers with severe skeletal abnormalities defines the disease as mucopolysaccharidosis VII. PLoS One. 2012;7(7):e40281.