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 for Squamous Cell Carcinoma
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.
More Horse Health
"Warmblood" Fragile Foal Syndrome
"Warmblood" fragile foal syndrome (FFS) is a connective tissue disorder resulting in joint laxity and extremely thin skin that is only loosely connected to the body. The skin is easily torn, resulting in lacerations, hematomas, and seromas across the foal. Affected foals are euthanized shortly after birth.
Androgen Insensitivity Syndrome
Androgen Insensitivity Syndrome (AIS) is an X-linked disorder of sexual development resulting in a female horse with XY chromosomes. Horses with AIS exhibit stallion-like behavior such as agression toward other horses, Flehman response and vocalization toward cycling mares.
Cerebellar Abiotrophy
Cerebellar Abiotrophy (CA) is a degenerative neurological disorder, due to the death of neurons in the brain. Symptoms (head tremors, lack of coordination, wide stances, exaggerated gain, difficulty rising and startling easily), typically appear in foals between six weeks and four months of age.
Chronic Idiopathic Anhidrosis Risk
Chronic Idiopathic Anhidrosis Risk (CIA) is the inability to sweat in response to increased body temperature, (AKA "non-sweater"). This condition is dangerous and sometimes life-threatening for horses, who rely on sweating for 65-70% of their temperature regulation.