Night Vision-Appaloosa Spotting Link Investigated

If you see spots before your eyes when you look at your Appaloosa, chances are your horse's night vision is as strong as any other horse. But if your Appaloosa is lacking spots on his blanket area, he might not be seeing much at all in the dark.


Microscopic images of horse chromosome 1. TRPM1 genes are highlighted in green.

That's because of the connection between certain homozygous forms of "leopard complex" spotting and congenital stationary night blindness (CSNB) in Appaloosa-patterned horses, recently discovered by researchers at the University of Tampa and the University of Saskatchewan. A single gene, named TRPM1, was determined to be the likely cause of both phenomena in the Appaloosa breed.

Today, that same research team, led by Rebecca Bellone, PhD, associate professor of biology at the University of Tampa, is back with additional studies, which aim to pinpoint the precise location of the mutation in the TRPM1 gene that causes both "leopard complex" spotting and night blindness.

"Our long-term goal has always been to identify the genetic mutation causing leopard complex spotting and CSNB so that a DNA test can become available, allowing breeders and owners to make informed breeding and management decisions," Bellone said.

Part of that process is locating the exact area in the genome (2.7 billion bases in the horse) where the mutation appears to occur, according to the researchers. Although their work has not yet led them to the precise mutation, they have been able to narrow it down to a region only 173 kb (173,000 DNA letters) in size. Before these latest experiments, they were looking at a previously defined region 10 Mb (10 million DNA letters) long, Bellone said.

"This sequencing has allowed us to identify other possible causative mutations for further investigation," she said, in addition to solidifying their previous conclusion that TRPM1 is the gene responsible for both leopard complex spotting and CSNB.

Through this research, Bellone and her team hope to understand not only which gene is responsible, but also what the role that gene plays in pigmentation and vision.

"If we can understand what TRPM1 is doing," she said, "that will give us clues as to what other genes might be involved with the variation in patterning observed with leopard complex spotting."

Not to be confused with the term "leopard Appaloosa," which is commonly used to describe horses that are full-body white with colored spots, leopard complex spotting describes a large array of spotting patterns. Also known as "appaloosa spotting," these patterns include snowcap blanket, few spot, varnish roan, spotted blanket, and, of course, leopard.

More information:

Appaloosa spotting pattern by LP gene

This diagram shows the full spectrum of patterning observed in Appaloosas. The horses in the upper row have coat patterns that indicate they are are heterozygous for LP, and therefore are not affected by CSNB. Note that they have white patterning with moderate to plentiful dark spotting. The lower row of this diagram shows Appaloosas with coat patterns that indicate they are homozygous for LP, and therefore affected by CSNB. Unlike the upper row horses, these have white patterning with few or no dark spots.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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