Severe combined immunodeficiency (SCID), an inherited condition primarily affecting Arabians, is characterized by an underdeveloped immune system that results in foals with elevated temperatures, respiratory stress, and diarrhea.
Phenotype: Severe combined immunodeficiency (SCID) foals are normal at birth but soon present signs such as elevated temperature, respiratory stress, and diarrhea at an early age, typically between 2-8 weeks of age. Affected foals do not survive past the first six months of life. Both male and female foals are equally affected.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal/Unaffected, SCID = Severe combined immunodeficiency
Breeds appropriate for testing: Arabian, Arabian crosses
Explanation of Results:
Horses with N/N genotype will not have severe combined immunodeficiency and cannot transmit this severe combined immunodeficiency variant to their offspring.
Horses with N/SCID genotype will not be affected by severe combined immunodeficiency, but are carriers. They may transmit this severe combined immunodeficiency variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing an affected foal.
Horses with SCID/SCID genotype will have severe combined immunodeficiency, a fatal condition.
$45 one test per animal
+ $15 each additional test from list below:
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Severe combined immunodeficiency (SCID) is a recessive genetic defect of the immune system that occurs in Arabian and part-Arab horses. The mutation responsible for SCID is a five base pair deletion in the DNA-dependent protein kinase gene resulting in a truncation of the protein. The genetic defect results in lack of activity of the enzyme DNA-dependent protein kinase (DNA-PK) which is critical for development of immune system diversity and its ability to protect against infections. SCID foals have increased susceptibility to infection by viral, bacterial, fungal and protozoan organisms. SCID foals are normal at birth but soon present signs such as elevated temperature, respiratory stress, and diarrhea at an early age, typically between 2-8 weeks of age. SCID is lethal and cannot be cured; affected foals do not survive past the first six months of life. Both male and female foals are equally affected. The prevalence of the SCID mutation is estimated to be between 1-8% in Arabian horses, varying by country.
Testing for this SCID variant can help breeders and owners to identify carrier horses and to select mating pairs accordingly to avoid producing affected foals. Matings between two SCID carriers have a 25% percent chance of producing SCID foals. The test also provides information to clinicians to differentiate between SCID and other immune system diseases arising from non-genetic circumstances such as inadequate levels of colostrum antibodies caused by failure of passive transfer.
Shin, E.K., Perryman, L.E., & Meek, K. (1997). A Kinase-Negative Mutation of DNA-PKcS in Equine SCID Results in Defective Coding and Signal Joint Formation. Journal of Immunology, 158(8), 3565-3569.
Bernoco, D., & Bailey, E. (1998). Frequency of the SCID gene among Arabian horses in the USA. Animal Genetics, 29(1), 41-42. doi: 10.1046/j.1365-2052.1998.00237.x
Piro, M., Benjouad, A., Tligui, N. S., El Allali, K., El Kohen, M., Nabich, A., & Ouragh, L. (2008). Frequency of the severe combined immunodeficiency disease gene among horses in Morocco. Equine Veterinary Journal, 40(6), 590-591. doi: 10.2746/042516408x333001
Tarr, C. J., Thompson, P. N., Guthrie, A. J., & Harper, C.J. (2013). The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Veterinary Journal, 46(4), 512-514. doi: 10.1111/evj.12177