Breeds Affected: Japanese Chin
Samples Accepted: Blood, Buccal Swabs
Disease Information: GM2 Gangliosidosis type I (B variant) (GM2GIb) is known as Tay-Sachs disease in humans. Affected Japanese Chin dogs first show symptoms of difficulty moving and keeping their balance, have vision problems, and altered mental status. In dogs the age of onset is between 1 and 2 years and the swift progression of the disease usually leads to humane euthanasia within just months after diagnosis.
Inheritance Information: GM2GIb is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/gm2g1b The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/gm2g1b carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
gm2g1b/gm2g1b The dog is affected. If bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/gm2g1b carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/gm2g1b x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/gm2g1b x N/gm2g1b) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (gm2g1b/gm2g1b) should not be used for breeding.
Test Information: This mutation test identifies a single base change in exon 8 of the HEXA gene.
Freeman, A.C., Platt, S.R., Vandenberg, M., Holmes, S., Kent, M., Rech, R., Howerth, E., Mishra, S., O’Brien, D.P., Wenger, D.: GM2 gangliosidosis (B variant) in two Japanese Chins: clinical, magnetic resonance imaging and pathological characteristics. J Vet Intern Med 27:771-6, 2013. Pubmed reference: 23731274. Doi: 10.1111/jvim.12118.
Sanders, D.N., Zeng, R., Wenger, D.A., Johnson, G.S., Johnson, G.C., Decker, J.E., Katz, M.L., Platt, S.R., O’Brien, D.P.: GM2 gangliosidosis associated with a HEXA missense mutation in Japanese Chin dogs: a potential model for Tay Sachs disease. Mol Genet Metab 108:70-5, 2013. Pubmed reference: 23266199. Doi: 10.1016/j.ymgme.2012.11.008.
Further information is available at the Online Mendelian Inheritance in Animals website.