Leopard Complex Spotting (LP) and Congenital Stationary Night Blindness (CSNB)

Leopard Complex Spotting (LP), also known as Coat Colour Appaloosa pattern or Appaloosa spotting, refers to the leopard-like coat pattern distinctive to the Appaloosa breed, characterized by a white coat flecked with small, dark spots. This trait is caused by an autosomal incompletely dominant mutation in the Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1) gene. The resulting phenotype varies depending on whether the horse is homozygous or heterozygous. Horses that are homozygous have typically little to no leopard spots, while heterozygous horses display pigmented spots within the white-patterned areas of their coat. The extent of white in leopard complex-patterned horses is influenced by other genes, including PATN1, for which testing is also available. Breeds most commonly associated with this gene include the American Miniature Horse, Appaloosa, Australian Spotted Pony, British Spotted Pony, Knabstrupper, Miniature Horse, Noriker, Pony of the Americas, Falabella and Thoroughbred.

Horses homozygous for the mutation are also affected by Congenital Stationary Night Blindness (CSNB), a condition that causes an inability to see in low-light conditions.