Leopard Complex & Congenital Stationary Night Blindess
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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 and Tannu Tuva Pony. Leopard Complex is also found at a lower frequency in the Miniature Horse, Spanish Mustang and Noriker breeds. The expression of Leopard Complex includes three main components: white spotting, progressive roaning of pigmented areas with age and pigmented leopard spots which can 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. Horses that are homozygous for Leopard also have a condition called Congenital Stationary Night Blindness (CSNB).
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, Forsyth G, Leeb T et al. Fine-mapping and mutation analysis for TRPM1: a candidate gene for leopard complex (LP) spotting and congenital stationary night blindness in horses. Briefings in Functional Genomics (2010) doi:10.1093/bfgp/elq002.
Bellone R R, Archer S, Wade C M et al. Association analysis of candidate SNPs in TRPM1 with leopard complex spotting (LP) and congenital stationary night blindness (CSNB) in horses. Animal Genetics 41 (Suppl 2): 207 (2010).