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Gene or Region: CXCL16 on ECA11: 50.08 Mb – 50.09 Mb (EquCab3.0)
Reference Variant: AGTG or “Resistant”
Mutant Variant: TCAA or TCGA or “Susceptible”
Affected Breeds: Thoroughbred, Saddlebred, Standardbred, Quarter Horse, Warmblood and others
Research Confidence: Preliminary - Strong correlation in early studies, association was present in multiple breeds with strong candidate genes in the region
Explanation of Results: EAVR/EAVR = homozgygous for Equine Arteritis Virus Resistance EAVR/n = heterozygous for Equine Arteritis Virus Resistance n/n = no variant detected
Equine Viral Arteritis is an infectious disease with a broad range of symptoms, though most horses will not display any overt signs. However, infection with EAV can result in abortions in pregnant mares, and some stallions persistently shed the virus through their semen. Infection prevalence has been reported to vary among breeds, indicating a genetic component to resistance/susceptibility.
The measured SNPs in CXCL16 were reported to be associated with susceptibility of CD3+ lymphocytes to EAV infection. When all four studied breeds were grouped together, the “AGTG” group of alleles was present in 0% of susceptible horses and 100% of resistant horses. Out of these resistant genotypes, 86% were non-shedder, whereas of the susceptible genotype, 74% were shedder. Thus, a horse that genotypes homozygous “AGTG” for all 4 of these SNPs are classified as at a lower risk for susceptibility to infection.
Sarkar S et al., “Allelic Variation in CXCL16 Determines CD3+ T Lymphocyte Susceptibility to Equine Arteritis Virus Infection and Establishment of Long- Term Carrier State in the Stallion.” (2016) PLOS Genetics | DOI:10.1371/journal.pgen.1006467.
Go YY et al., “Genome-wide association study among four horse breeds identifies a common haplotype associated with in vitro CD3+ T cell susceptibility/resistance to equine arteritis virus infection.” (2011) J Virol. 85: 13174-84. PMID: 21994447
Congenital Stationary Night Blindness (CSNB) is an inherited disorder in horses characterized by an inability to see in low-light or dark conditions. This condition is present from birth and does not worsen over time. Common indicators include a horse’s reluctance to enter dark environments, difficulties in locating food and water in the dark, and a propensity for nighttime injuries.
Equine herpesviruses are DNA viruses that are found in most horses all over the world, often without any serious side effects. Following infection of Equine Herpesvirus Type 1 (EHV-1) some horses then suffer Equine Herpesvirus Myeloencephalopathy (EHM), which is is accompanied by serious and sometimes fatal neurological effects. EHM in horses can have serious neurological symptoms on affected horses.
Equine Metabolic Syndrome (EMS) is a wide-spread issue in the horse population. Primarily characterized by hyperinsulinemia (excess insulin circulating in the blood in relation to glucose levels), this metabolic disorder is often present in obese horses and ponies and can be challenging to diagnose as it can be misdiagnosed as "Cushing's" (a pituitary disfunction).
