A popular source of symmetric white patterning called Leopard Complex (LP), also known as Appaloosa spotting, is characteristic of the Appaloosa and Pony of the Americas breeds. Other breeds around the world that exhibit this pattern include the British Spotted Pony, Knabstrupper, Noriker, and Tannu Tuva Pony. Leopard Complex is also found at a lower frequency in the American Miniature Horse and Spanish Mustang breeds. The expression of Leopard Complex includes several components: mottled skin around the muzzle, anus, genitalia, and eyes, and progressive roaning of pigmented coat areas with age. White spotting may also be present, with pigmented leopard spots tending to occur on the white spotting background of heterozygous horses. . The mutation is an incomplete dominant and expression of Leopard Complex is variable ranging from absent to extreme white patterning. The amount of white present is not dosage related, such that homozygous horses can have minimal expression of white patterning. The variability in the amount of white on leopard complex patterned horses is controlled by other genes, one of which is PATN1. Horses that are homozygous for Leopard Complex also have Congenital Stationary Night Blindness (CSNB) which is the inability to see in low to no-light conditions.
The genetic basis for Leopard Complex has been identified. The VGL is licensed to offer the test for the specific mutation. Results are reported as:
|N/N||no copies of Leopard Complex (Appaloosa) spotting.|
1 copy of Leopard Complex mutation, 50% of offspring will inherit the Leopard gene*.
2 copies of Leopard Complex mutation, all offspring will inherit the Leopard gene*. Horse has congenital stationary night blindness (CSNB).
* Expression of Leopard Complex is variable and white patterning may not be present in all horses that inherit the gene.Reference:Bellone, R.R., Holl, H., Setaluri, V., Devi, S., Maddodi, N., Archer, S., Sandmeyer, L., Ludwig, A., Foerster, D., Pruvost, M., Reissmann, M., Bortfeldt, R., Adelson, D.L., Lim, S.L., Nelson, J., Haase, B., Engensteiner, M., Leeb, T., Forsyth, G., Mienaltowski, M.J., Mahadevan, P., Hofreiter, M., Paijmans, J. L.A., Gonzalez-Fortes, G., Grahn, B., & Brooks, S.A. (2013) Evidence for a Retroviral Insertion in TRPM1 as the Cause of Congenital Stationary Night Blindness and Leopard Complex Spotting in the Horse. PLoS ONE 8(10):e78280 (doi:10.1371/journal.pone.0078280).