Dwarfism in Labrador Retrievers - skeletal dysplasia 2 (SD2)

The dogs affected by the skeletal dysplasia 2 have typical short legs and normal length and width of the body.  No secondary health problems have been observed. The hearing and the eyesight of the dogs are not affected und they have no other problems with joints.

According to the study by Fischknecht at al. 2013, there were characterized 34 affected dogs.  In most cases the forelegs were more shortened than the hind legs. The width and length of the body were normal. The affected dogs presented the working line of Labrador Retrievers. Male affected dogs mostly had shoulder heights of less than 55 cm and female affected dogs mostly had shoulder heights of less than 50 cm, while the international breed standards (FCI) call for 56-57 cm in males and 54-56 cm in females.

The disease is caused by mutation c.143G>C in COL11A2 gene resulting in the exchange of a proline for an arginine (p.R48P). The mutation has a minor effect on the function of exprimized COL11A2-collagen, type XI, which explains the mild phenotype of the disease without any other severe health problems (Fischknecht at al., 2013).

Mutation that causes SD2 in labrador retrievers is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

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References:

Frischknecht M, Niehof-Oellers H, Jagannathan V, Owczarek-Lipska M, Drögemüller C, et al. (2013) A COL11A2 Mutation in Labrador Retrievers with Mild Disproportionate Dwarfism. PLoS ONE 8(3): e60149. doi:10.1371/journal.pone.0060149