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Horse Severe Combined Immuno Deficiency (SCID)
| Acronym: | SCID |
| Gene: | PRKDC |
| Mutation: | c.9478_9482del |
| Inheritance: | Autosomal Recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Severe combined immunodeficiency is one of the most common genetic diseases among Arabian and part-Arabian horses. This disease causes a complete absence of certain immune cells such as B lymphocytes and T lymphocytes which makes horses incapable of antigen-specific immunity. Horses affected with SCID usually die in the first 6 months due to their high susceptibility to infections. Horses with SCID generally start to show symptoms 2-3 months after birth considering that they still have passively transferred immunity from their mother. The most common symptoms are elevated temperature and respiratory problems although symptoms depend on the type of infection. Since SCID leaves their immune system unprotected, horses are not able to defend against bacterial, fungal, viral, or protozoic infections. Mutation that causes this disease is in the DNA - dependent protein kinase (DNA-PK) gene responsible for the development of the immune system.
This type of primary immunodeficiency found in Arabian horses is inherited as an autosomal recessive trait, meaning both mutated DNA-PK genes are required for the disease to develop. Horses carrying one mutated and one normal gene appear normal, without signs of the disease. There is no cure or treatment for SCID, and the only way of prevention and precise diagnosis is early detection by genetic testing that can help identify horses that are affected or carry the specific mutation and help in the future selection of mating pairs.
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:
Ayad, A., Almarzook, S., Besseboua, O., Aissanou, S., Piórkowska, K., Musiał, A. D., Stefaniuk-Szmukier, M., Ropka-Molik, K. (2021). Investigation of Cerebellar Abiotrophy (CA), Lavender Foal Syndrome (LFS), and Severe Combined Immunodeficiency (SCID) Variants in a Cohort of Three MENA Region Horse Breeds. Genes, 12(12), 1893. https://doi.org/10.3390/genes12121893
Bugno-Poniewierska, M., Stefaniuk-Szmukier, M., -Kajtoch, A. P., Fornal, A., Piórkowska, K., Ropka-Molik, K. (2019). Genetic screening for cerebellar abiotrophy, severe combined immunodeficiency and lavender foal syndrome in Arabian horses in Poland. Veterinary journal (London, England : 1997), 248, 71–73. https://doi.org/10.1016/j.tvjl.2019.04.012
AbouEl Ela N.A., El-Nesr K.A., Ahmed H.A., Brooks S.A. (2018). Molecular Detection of Severe Combined Immunodeficiency Disorder in Arabian Horses in Egypt. J Equine Vet Sci. 68:55-58. doi:10.1016/j.jevs.2018.05.210