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Ocular Squamous Cell Carcinoma (SCC)
| Acronym: | SCC |
| Gene: | DDB2 |
| Mutation: | c.1013C>T |
| Inheritance: | Autosomal Recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Ocular squamous cell carcinoma (SCC) is an inherited eye disease that affects several breeds of horses. Horses with SCC have a tumour of the limbus (junction of the cornea and sclera), third eyelid, and/or upper and lower eyelids, which, if left untreated, can spread into eye tissue and cause visual impairment. There is no unique answer to the cause of this disease, but factors that increase the risk are UV exposure, pigmentation, and genetics. Some horse breeds have a higher incidence of SCC, suggesting that genetic factor plays a crucial role. One of the most frequent genetic mutations is in the damage-specific DNA binding protein 2 (DDB2) gene, responsible for binding DNA after UV damage. The missense mutation in the DDB2 gene causes loss of DNA anchor, so the mutated protein cannot bind damaged DNA, which accumulates in the cell leading to tumour formation.
SCC is inherited as an autosomal recessive trait, meaning two copies of the mutation are needed for a horse to be affected. However, horses homozygous for the mutation will not always be affected but have a much higher risk for tumour development. SCC affects several horse breeds, including Haflinger, Belgians, Rocky Mountain, Appaloosa, and Percheron. The disease is treatable, so genetic testing can help with early detection and better prognosis, as well as reduce the chances of breeding horses that have a high risk of developing this tumour.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Kaps, S., Richter, M., Philipp, M., Bart, M., Eule, C., & Spiess, B. M. (2005). Primary invasive ocular squamous cell carcinoma in a horse. Veterinary Ophthalmology, 8(3), 193–197. doi:10.1111/j.1463-5224.2005.00358.x
Knickelbein, K. E., Lassaline, M. E., Singer‐Berk, M., Reilly, C. M., Clode, A. B., Famula, T. R., … Bellone, R. R. (2019). A missense mutation in damage‐specific DNA binding protein 2 is a genetic risk factor for ocular squamous cell carcinoma in Belgian horses. Equine Veterinary Journal. doi:10.1111/evj.13116