CSNB / Leopard Spotting

The Appaloosa spotting pattern, also known as Leopard Complex spotting (LP) includes a highly variable group of white spotting- or depigmentation patterns in horses. Appaloosa horses have three additional identifiable characteristics: mottled skin around the muzzle, anus and genitalia, striped hooves and white sclera round the eyes. The Appaloosa pattern is the result of an incompletely dominant mutation in the TRPM1 gene, also known as the LP gene. The LP gene allows for the expression of the various leopard complex spotting patterns while other genes determine the extent (or amount) of white. The CSNB / Leopard Spotting test (P311) tests for the status of the LP (TRPM1) gene. This gene has two variants (alleles). The allele LP is incomplete-dominant and expression of the Appaloosa pattern is variable, ranging from absent to extremely white patterning. At least one copy of the LP allele allows the expression of the Appaloosa pattern. The amount of white present is not dosage related, horses with two copies of the LP allele can have minimal expression of white patterning. The recessive allele N does not have an effect on the basic colour. The variability in the amount of white on Appaloosa-coloured horses is controlled by other genes, one of which is PATN1. Horses that have one copy of the LP allele, in combination with at least one copy of the PATN1 allele most often have a Leopard or a near Leopard pattern. Horses that have two copies of the LP allele in combination with at least one copy of the PATN1 allele most often have a Few-spot or near Few spot pattern. Horses that have two copies of the LP allele suffer from Congenital Stationary Night Blindness (CSNB), which is the inability to see in low to no-light conditions.

The CSNB / Leopard Spotting test encloses the following results, in this scheme the results of the CSNB / Leopard Spotting test are shown in combination with the possible results for the Coat Colour Appaloosa Pattern-1 (PATN1) test.