Leopard, ERU & CSNB

• 30 to 40 - hair roots - envelope

• 5 mL - blood - K3 EDTA tube

Turnaround time

• 2 to 5  working days

Results description

The DNA test verifies the presence of the dominant LP Gene (designated LP) and presents results as one of the following:                                                            

• N/ - Negative for LP. Absence of the dominante LP gene, non spotted horse. Lower risk to develop Equine Recurrent Uveitis (ERU) and Congenital N/ Stationary Night Blindness (CSNB) associated to Leopard.

• LP/N - Positive heterozygous for LP. Presence of one copy of the incomplete dominant LP gene responsible spotted coat (Appaloosa coat pattern). Horses have high risk to develop Equine Recurrent Uveitis (ERU). The horse can pass the LP gene to 50% of their progeny when bred.

• LP/ - Positive homozygous for LP. Presence of two copies of the incomplete dominant LP gene responsible for spotted coat (Appaloosa coat pattern). Additionally horses have highest risk to develop Equine Recurrent Uveitis (ERU) and Congenital Stationary Night Blindness (CSNB). The horse will LP/LP pass the LP gene to 100% of its offspring. Risk for ERU associated to LP is evaluated LP/LP > LP/N > N

Additional information

The white patterns called Leopard Complex (LP), also know as Appaloosa spotting, has an high variable expression ranging from absent to extreme white patterning. 

The expression of Leopard Complex includes several effects on the horse's coat: speckled/mottled skin around the eyes, muzzle, anus, genitalia, and eyes, and progressive roaning (varnish roan) of pigmented coat areas with age. White spotting may also be present, with pigmented leopard spots tending to occur on the white spotting background of heterozygous horses.

The inheritance of this coat colour trait is incomplete dominant. The amount of white present is not dosage related, such that homozygous horses can have minimal expression of white patterning. The variability in the amount of white on leopard complex patterned horses is controlled by other genes, one of which is Pattern 1.  /PATN1, the coat pattern spotting. 

Horses that are homozyous for the Leopard Complex  develop Congenital Stationary Night Blindness (CSNB) which is the inability to see in low to no-light conditions.

Equine Recurrent Uveitis (ERU), also known as moon blindness, is also associated to the LP genetic variant. ERU is characterised by repeated episodes of inflammation of the iris, ciliary body, and choroid. The cumulative effects of the immune mediated process can lead to glaucoma, cataracts, and complete loss of vision. 

ERU is the most common cause of blindness in horses. The LP test is the most effective genetic test to ascertain risk for ERU. 

Risk for ERU based on this genetic test can be evaluated as LP/LP > LP/N > N/N. 

• Horses homozygous for LP mutation are the highest risk of developing ERU.
• Horses heterozygous for LP mutation are at higher risk of developing ERU than those with the mutation.

The LP variant is closely identified to the Appaloosa breed, though has indicated has a very ancient genetic variant. European cave paintings have recorded spotted horses and archaegenetic studies have identified the LP genetic variant in European horses of the Pleistocene and Copper Age.

The LP genetic variant can be found in many different breeds such as pony of Americas breeds, British Spotted Pony, Knabstrupper, Noriker, Tannu Tuva Pony, American Miniature Horse, Mustang breeds and Tiger horses . 

References

Bellone, R.R., Holl, H., Setaluri, V., Devi, S., Maddodi, N., Archer, S., Sandmeyer, L., Ludwig, A., Foerster, D., Pruvost, M., Reissmann, M., Bortfeldt, R., Adelson, D.L., Lim, S.L., Nelson, J., Haase, B., Engensteiner, M., Leeb, T., Forsyth, G., Mienaltowski, M.J., Mahadevan, P., Hofreiter, M., Paijmans, J.L., Gonzalez-Fortes, G., Grahn, B., Brooks, S.A.: Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse. PLoS One 8:e78280, 2013. 

Bellone RR. Genetic Testing as a Tool to Identify Horses with or at Risk for Ocular Disorders. Vet Clin North Am Equine Pract. 2017;33(3):627–645. doi:10.1016/j.cveq.2017.08.005

Pruvost M. et al.. Genotypes of predomestic horses match phenotypes painted in Paleolithic works of cave art. Proc. Natl. Acad. Sci. 108, 18626–18630 (2011). [PMC free article] [PubMed] [Google Scholar]