Leopard Print (Appaloosa)

Description

Leopard complex spotting (LP) is the gene behind the spotted coat patterns of the Appaloosa and related breeds. Horses carrying LP can show a wide range of patterns, from a white blanket over the hips to a fully spotted leopard coat. LP horses also typically show three other characteristics: mottled skin around the muzzle, eyes and genitals, vertically striped hooves, and white sclera around the eye.

The pattern is ancient. Spotted horses appear in European cave paintings more than 20,000 years old, and the LP mutation has been found in DNA from prehistoric horses, long before domestication. It is best known in the Appaloosa, named for the Palouse River region of the Nez Perce people, who selectively bred spotted horses, and it also occurs in breeds such as the Knabstrupper, the Noriker and the Pony of the Americas.

LP was mapped to the TRPM1 gene in the late 2000s by Dr. Rebecca Bellone and colleagues. The causal mutation was later identified as a retroviral insertion within TRPM1. This test detects that mutation directly.

One copy or two

LP is incompletely dominant, so the number of copies affects the pattern. Horses with one copy (n/LP) tend to have dark spots within their white areas, as in leopard and spotted-blanket patterns. Horses with two copies (LP/LP) tend to have little or no spotting within the white, as in few-spot and snowcap patterns. How much white a horse shows depends on other genes, especially PATN1.

PATN1 and the amount of white

A variant in the RFWD3 gene, known as Pattern-1 (PATN1), greatly increases the amount of white in horses that carry LP. PATN1 acts in a dominant fashion, so one copy is enough. An n/LP horse with PATN1 is typically leopard or near-leopard, and an LP/LP horse with PATN1 is typically few-spot. PATN1 has no visible effect without LP, so a solid horse can carry PATN1 and pass it on. This is why a solid parent can produce a leopard foal when bred to an LP horse. PATN1 is tested separately.

Congenital Stationary Night Blindness (CSNB)

The same LP mutation that causes the spotting also causes Congenital Stationary Night Blindness, a condition present from birth that impairs vision in dim light and darkness. CSNB is recessive: every horse with two copies of LP (LP/LP) has CSNB, and horses with one copy do not. Affected horses often cope well in daylight but may be anxious or hesitant at night or in dark barns and trailers. Breeding two n/LP horses gives each foal a 25% chance of being LP/LP.

Appaloosas are also predisposed to Equine Recurrent Uveitis, an inflammatory eye disease. It is a separate condition and is not detected by this test.

Why test for LP?

Testing confirms whether a horse carries LP, which is especially useful for horses with minimal or no visible spotting. It also shows whether a horse is LP/LP and therefore affected by CSNB, and helps breeders plan pairings to produce the patterns they want.

Possible results

Breeds Affected

Appaloosa, Knabstrupper, Pony of the Americas, Noriker, Nez Perce Horse, Tiger Horse, Colorado Ranger, Walkaloosa, British Spotted Pony, Miniature Horse, Spanish Mustang

Reference

Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse.

Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus).

Variant in the RFWD3 gene associated with PATN1, a modifier of leopard complex spotting.

Related Tests

• Pattern-1 (PATN1) — determines how much white an LP horse will show
• Red/Black Factor — the base color showing through the spots
• Agouti — completes the base color picture

Breeding for pattern? The Appaloosa Pattern Panel covers LP and PATN1 together for $40.