Ocular squamous cell carcinoma / SCC risk (DDB2-related) - Horse

What does this test examine?

This genetic test examines the DDB2 c.1013C>T risk variant in horses. The condition is known as ocular squamous cell carcinoma, SCC and equine eye cancer.

What does this mean for the horse?

DDB2 is involved in repairing DNA damage caused by UV light. The c.1013C>T variant reduces this protection and increases the risk of ocular SCC, especially in horses with two copies. Tumours often develop on or around the eye, including the limbus, third eyelid, eyelids or conjunctiva, and can cause irritation, discharge, vision problems and damage to the eye.

This test does not predict a certain tumour. UV exposure, pigmentation and other factors remain important. The DNA result does help identify horses with increased genetic risk.

Practical value of this test

• The test distinguishes horses with no risk variant, one copy and two copies.
• Breeders can plan matings to avoid foals with two copies of the risk variant.
• In horses with two copies, the result supports targeted attention to eye checks and preventive protection from sunlight.

Inheritance

The DDB2 risk variant acts as an autosomal recessive risk factor with incomplete penetrance. Horses with two copies have the highest genetic risk; horses with one copy can pass the variant on.