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Androgen Insensitivity Syndrome 2 (AIS2) in Tennessee Walking Horse (AR4)
| Acronym: | AR4 |
| Gene: | AR |
| Mutation: | c.183delT |
| Inheritance: | X-Linked recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Androgen insensitivity syndrome 2 (AIS2) is an inherited sexual development disease that affects several horse breeds. Male horses with AIS2 have an XY chromosomal constitution, undescended testes, and female secondary sexual characteristics, including female external genitalia. This disease causes male horses to be sterile and appear phenotypically female. AIS2 is caused by genetic mutations in the androgen receptor (AR) gene responsible for mediating androgenic functions during development and after puberty when secondary sexual characteristics become apparent. Five different known mutations in the AR gene cause this disease in horses, mostly deletions and missense mutations, resulting in either a truncated protein or reduced amount of functional protein, leading to physical characteristics of the disease.
AIS2 is inherited as an X-linked recessive disease, meaning that female horses are carriers of the disease. Therefore, only male horses with one copy of the mutation will be affected and sterile. AIS2 affects several horse breeds, including Quarter Horse, Thoroughbred, Tennessee Walking Horse, and Warmbloods. The disease is incurable, but early detection by genetic testing can help identify female carriers of the mutation and prevent further breeding by careful 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 (female) or hemizygous state (male) (i.e. only healthy allele on X chromosome). 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 mutated allele in homozygous state (female) or hemizygous state (male) (i.e. only mutated allele on X chromosome). 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.
** Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Bolzon, C., Joonè, C. J., Schulman, M. L., Harper, C. K., Villagómez, D. A. F., King, W. A., & Révay, T. (2016). Missense Mutation in the Ligand-Binding Domain of the Horse Androgen Receptor Gene in a Thoroughbred Family with Inherited 64,XY (SRY+) Disorder of Sex Development. Sexual Development, 10(1), 37–44. doi:10.1159/000444991
Villagomez, D. A. F., Welsford, E. G., King, W. A., & Revay, T. (2020). Androgen Receptor Gene Variants in New Cases of Equine Androgen Insensitivity Syndrome. Genes, 11(1), 78. doi:10.3390/genes11010078
Welsford, G. E., Munk, R., Villagómez, D. A. F., Hyttel, P., King, W. A., & Revay, T. (2017). Androgen Insensitivity Syndrome in a Family of Warmblood Horses Caused by a 25-bp Deletion of the DNA-Binding Domain of the Androgen Receptor Gene. Sexual Development, 11(1), 40–45. doi:10.1159/000455114