Squamous Cell Carcinoma (SCC)
Gene or Region: DDB2
Reference Variant: C
Mutant Variant: T
Affected Breeds: Belgian and Haflinger
Research Confidence: Preliminary - Correlates in studies with humans
Explanation of Results: sccr/sccr = homozygous for Squamous Cell Carcinoma, 80% likely affected sccr/n = heterozygous for Squamous Cell Carcinoma, carrier n/n = no variant detected
General Information
Squamous Cell Carcinoma is the most common cause of eye cancer in horses. It is also responsible for a large percentage of tumors throughout other parts of the equine body. A recent correlation was discovered between Squamous Cell Carcinoma (SCC) and the DDB2 genetic region. A mutation identified in that region is hypothesized to affect the protein's active role of identifying and signaling DNA regions damaged by UV light for additional “repair” protein mechanisms which attempt to restore the region and thus, prevent tumor or cancer formation. This mutation for Squamous Cell Carcinoma is currently thought an autosomal recessive disorder, thus a horse must inherit two copies (scc/scc) to be at a greatly increased risk for cancer. Studies indicate that horses with two copies of SCC (sccr/sccr) are 80% likely to be affected by Squamous Cell Carcinoma. Horses with only one allele (sccr/n) are known as carriers due to their ability to produce affected offspring.
While early studies indicate a strong correlation between the SCC mutation of DDB2 and Haflinger and Belgian horses, current studies will continue to assess the occurrence in other breeds as well.
References
Lassaline M, Cranford TL, Latimer, CA, & Bellone R. (2015) Limbal squamous cell carcinoma in Haflinger horses. Vet Ophthalmol 18(5) 404-408.
Bellone RR, Liu J, Petersen JL, Mack M, Singer-Berk M, Drögemüller C, Malvick J, Wallner B, Brem G, Penedo MC, & Lassaline M. (2017) A Missense Mutation in Damage-specific DNA Binding Protein 2 Is a Genetic Risk Factor for Limbal Squamous Cell Carcinoma in Horses. Int. J. Cancer 141(2):342-353.
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