Color: A wide range of white spotting patterns exist: some horses show only a scattering of white flecks over the body, others have broad areas of white with some dark spots, while some horses are nearly completely white with only a few dark spots. Even if mostly solid colored, horses with the LP mutation will have mottled skin around the mouth, anal-genital region, white stripes on the hooves, white sclera in the eyes, and can exhibit progressive “varnish roan,” which is unrelated to normal roaning (RN).
Samples Accepted: Blood, Hair
Locus Information: The mutation responsible for this color pattern also affects a cell-signalling pathway in the eye, resulting in homozygous horses having problems seeing in low light (Congenital stationary night blindness, CSNB).
Test Information: This test is based on an insertion mutation in the TRPM1 gene. The appaloosa color pattern is incomplete autosomal dominant, as any animal with one copy of the allele will have the pattern, although the extent may vary according to the presence of modifier genes (eg. PATN1). A horse with two copies of the the mutation will have areas of white with fewer colored spots than those with one copy of the mutation. Animals with two copies will also have congenital stationary night blindness (CSNB).
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., Gonzalez-Fortes, G., Grahn, B., Brooks, S.A.: 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:e78280, 2013. Pubmed reference: 24167615. Doi: 10.1371/journal.pone.0078280.
Further information is available at the Online Mendelian Inheritance in Animals website.