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Apaloosa Pattern / Congenital Stationary Night Blindness (CSNB)
| Acronym: | CSBN |
| Gene: | TRPM1 |
| Mutation: | 1378 bp insertion |
| Inheritance: | Autosomal Incompletely Dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Appaloosa Pattern also referred to as Leopard complex spotting (LP) is a white spotting pattern in horses characterized by the absence of pigment in the coat. This coat pattern is common in Appaloosas, Miniature Horses, Knabstruppers, Norikers, and some other horse breeds. Leopard pattern is often a wanted trait among horse breeders, but like other coat traits, it has a pleotropic effect meaning it may also cause some other traits or defects. Appaloosa pattern is often connected to Congenital Stationary Night Blindness (CSNB). CSNB is characterized by a non-progressive impaired vision in dark conditions and is present since birth. The disease is the result of abnormal cell signaling from the rods, resulting in night blindness in affected horses. A genetic mutation that causes both, coat spotting pattern and night blindness, is detected to be a large insertion in the Transient Receptor Potential Cation Channel (TRPM1) gene. TRPM1 encodes an important calcium ion channel that plays an important role in cell signaling in eye cells and pigment cells.
Leopard spotting (LP) in horses has an autosomal incompletely dominant mode of inheritance meaning individuals that are carrying at least one copy of the mutated gene will show the absence of pigment in the coat and hence, appaloosa pattern. However, horses with both mutated genes may display more characteristic spotting patterns than those carrying only one gene. Night Blindness (CSNB) in horses has an autosomal recessive mode of inheritance meaning both copies of the mutated gene are required for the disease to develop. Horses that carry only one mutated TRPM1 gene will show leopard spots, but will not develop the disease. Early detection by genetic testing can help identify carriers of the mutation and help breeders in further selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
Healthy with Normal pattern |
Horse is healthy and does not have the gene with the Apaloosa pattern associated mutation. |
Healthy Carrier with Apaloosa pattern |
Horse has one copy of the gene with the Apaloosa pattern associated mutation. Horse does not have the Night Blindness disease but has Apaloosa pattern. |
Affected with Apaloosa pattern |
Horse has two copies of the gene with the Apaloosa pattern associated mutation. Horse has the Night Blindness disease and Apaloosa pattern. |
References:
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., … 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. https://doi.org/10.1371/journal.pone.0078280
Sandmeyer, L. S., Bellone, R. R., Archer, S., Bauer, B. S., Nelson, J., Forsyth, G., Grahn, B. H. (2012). Congenital stationary night blindness is associated with the leopard complex in the Miniature Horse. Veterinary ophthalmology, 15(1), 18–22. https://doi.org/10.1111/j.1463-5224.2011.00903.x
Ludwig, A., Reissmann, M., Benecke, N., Bellone, R., Sandoval-Castellanos, E., Cieslak, M., Fortes, G. G., Morales-Muñiz, A., Hofreiter, M., Pruvost, M. (2015). Twenty-five thousand years of fluctuating selection on leopard complex spotting and congenital night blindness in horses. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1660), 20130386. https://doi.org/10.1098/rstb.2013.0386