Turnaround: 3-5 business daysTurnaround: 7-10 business days
Price: $40.00Price: £35.00
Breeds: Appaloosa, Appaloosa Cross, Arabian, Arabian Cross, Arabian/Pinto, Belgian Draft Horse, Clydesdale, Connemara Pony, German Riding Pony, Haflinger, Miniature Appaloosa, Mixed Breed, Mixed Breed (Horse), Pinto, Quarter Cross, Unspecified
Description
Squamous cell carcinoma (SCC) is the most common cancer of the equine eye. It often begins at the limbus, where the cornea meets the white of the eye, and can also develop on the third eyelid (nictitating membrane). Left untreated, SCC can invade the cornea, impair vision, and lead to loss of the eye. Horses with light pigmentation around the eyes are generally at higher risk, and certain breeds show a particularly high occurrence, suggesting a genetic predisposition.
A missense variant in the damage-specific DNA binding protein 2 gene (DDB2 c.1013C>T, p.Thr338Met) has been identified as a recessive genetic risk factor for ocular SCC. The DDB2 protein helps recognize and repair DNA damaged by ultraviolet (UV) light, and functional studies have shown that the altered protein can no longer recognize UV-damaged DNA. This links the genetic risk to sun exposure. The variant was first identified in Haflingers and has since been associated with ocular SCC in Belgian draft horses and Rocky Mountain Horses. In a study of Haflingers with third eyelid SCC, 88% of affected horses were homozygous for the variant.
Horses with two copies of the variant are at significantly increased risk, but not all of them will develop SCC, and some affected horses do not carry the variant. The variant has not been associated with SCC in Appaloosas or Arabians. Horses identified as at risk benefit from UV protection, such as fly masks, and regular eye examinations so that any tumors can be caught and treated early.
Possible results
| Genotype | Description |
|---|---|
| R/R | At Risk: Horse has two copies of the DDB2 risk variant and is at increased risk of developing ocular SCC. All offspring will inherit the variant. |
| R/n | Carrier: Horse has one copy of the DDB2 risk variant and is not considered at increased genetic risk of developing ocular SCC. Each offspring has a 50% chance of inheriting the variant. |
| n/n | Clear: Horse does not carry the DDB2 risk variant and cannot pass it on to offspring. |
Breeds Affected
Belgian, Belgian Warmblood, Connemara Pony, Haflinger, Holsteiner, Rocky Mountain Horse
Reference
[PMID: 28425625]
[PMID: 29999543]