Gangliosidosis (GM2) in Toy Poodles

This disease, also known as Sandhoff-like disease, is caused by GM2 ganglioside accumulation in various tissues due to a deficiency of the enzyme hexosaminidase, which is responsible for breaking down the GM2 ganglioside into its components. The disease is characterized by progressive neuromuscular dysfunction and growth failure at an early age.

The causal mutation in toy poodles is a deletion of one guanine base pair in exon 3 of the HEXB gene (c.283delG) resulting in a reading frame shift and premature insertion of  a stop codon.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Rahman, M.M., Chang, H.S., Mizukami, K., Hossain, M.A., Yabuki, A., Tamura, S., Kitagawa, M., Mitani, S., Higo, T., Uddin, M.M., Uchida, K., Yamato, O. : A frameshift mutation in the canine HEXB gene in toy poodles with GM2 gangliosidosis variant 0 (Sandhoff disease). Vet J 194:412-416, 2012. Pubmed reference: 22766310