Leopard complex and PATN1

What it looks like

Leopard complex includes much more than an all-over spotted coat. A horse may have a white blanket over the hindquarters with colored spots, very few spots, or a progressive increase in white hairs known as varnish roaning. Mottled skin, striped hooves and a conspicuous white sclera, the white part of the eye, can support identification. No single feature reveals the whole genetic result, and little white at birth does not exclude later changes.

Sources for this explanation [1]

What happens biologically

LP names a variant caused by an extra stretch of DNA inserted into TRPM1. This gene has roles in pigmentation and in signaling in the retina, the light-sensitive tissue at the back of the eye. Other DNA regions modify how much of the coat becomes white. One important modifier is PATN1, associated with a variant near or within RFWD3.

The distinction matters: LP allows leopard-complex features, while PATN1 helps determine their white extent when LP is present. For example, a horse may carry PATN1 but have no LP; PATN1 alone does not give that horse a leopard or Appaloosa pattern, although it can still be inherited by a foal.

Sources for this explanation [2] · [4]

Inheritance and DNA testing

On an LP test, N means the LP variant was not detected on that copy. N/N means no LP copy; LP/N means one LP copy; LP/LP means two, one from each parent. One-copy horses generally have colored spots within their white areas. Two-copy horses tend to have fewer such spots or none. Two LP copies do not automatically mean more white, because other genetic modifiers also matter.

A tested LP/N horse has a one-in-two chance of passing LP on at each conception, while an LP/LP horse passes it to every foal. Testing LP and PATN1 together gives more information about possible patterns, but cannot predict the exact number or position of spots. The LP copy number also matters for eye health, as explained below.

Sources for this explanation [3] · [1]

Confusions, limits and health

Two LP copies, the LP/LP result, cause congenital stationary night blindness: reduced vision in dim light, present from birth and usually not worsening with age. This is different from equine recurrent uveitis, inflammation inside the eye that can recur and damage vision. Some LP populations, especially horses with two copies, have increased uveitis risk, but color does not diagnose an active episode. Discuss low-light management and eye monitoring with the veterinarian.

Sources for this explanation [1] · [2]

Where the explanations come from

Laboratory resources explain which variants are tested and how to read their results. Research papers describe the evidence, discoveries and remaining uncertainties. Each article links its explanations to the relevant sources. Published titles stay in their original language so you can find the exact work.

1. 1 · Laboratory explanation

   UC Davis VGL — Leopard complex, congenital stationary night blindness and uveitis

2. 2 · Research paper

   Bellone et al. (2013) — Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse

3. 3 · Laboratory explanation

   UC Davis VGL — Appaloosa Pattern-1

4. 4 · Research paper

   Holl et al. (2016) — Variant in the RFWD3 gene associated with PATN1, a modifier of leopard complex spotting