Common Symptoms
GM2 gangliosidosis is an inherited Lysosomal Storage Disorder affecting Japanese chins. Affected dogs have insufficient activity of the Enzyme hexosaminidase A, which is responsible for breaking down specific carbohydrates in the cells. As a result, there is an accumulation of a glycoprotein, GM2 ganglioside in cells, especially in cells of the nervous system, including the brain. Affected dogs typically present with symptoms of neurologic disease around 15 to 18 months of age. Symptoms include loss of balance, altered mental state and vision loss. Once an affected dog begins to show signs of the disease, the disease progression is rapid and dogs usually die within several months of initial presentation.
Breed-Specific Information for the Japanese Chin
The Mutation of the HEXA gene associated with GM2 gangliosidosis (Japanese chin type) has been identified in Japanese chins. Though the exact frequency in the overall Japanese chin population is unknown, approximately 4% out of 128 healthy, unrelated Japanese chins were carriers of the mutation.
Testing Tips
Genetic testing of the HEXA gene in Japanese chins will reliably determine whether a dog is a genetic Carrier of GM2 gangliosidosis (Japanese chin type). GM2 gangliosidosis (Japanese chin 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 HEXA 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. Japanese chins 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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Sanders DN, Zeng R, Wenger DA, Johnson GS, Johnson GC, Decker JE, Katz ML, Platt SR, O’Brien DP. GM2 gangliosidosis associated with a HEXA missense mutation in Japanese Chin dogs: A potential model for Tay Sachs disease. Mol Genet Metab. 2013 Jan;108(1):70-5. doi: 10.1016/j.ymgme.2012.11.008.
[PubMed: 23266199]
