Genetics and characteristics
Androgen insensitivity syndrome (AIS) is an inherited sex development disease that affects several breeds of horses. Horses with AIS appear physically female but have sex chromosomes of a male horse. The gonads of the affected females vary from fertile ovaries to dysgenetic testes. AIS is caused by a genetic mutation in the sex-determining region Y (SRY) gene responsible for male-typical sex development and determination of sex. The deletion mutation in the SRY gene causes a complete reversal of sex, and the severity of the disease depends on the size of the deleted gene area.
AIS is inherited as a Y-linked disease, meaning that the mutation is located on the Y chromosome in a male horse. Because only males have a Y chromosome, in this type of inheritance, a mutation can only be passed from father to son. AIS affects several horse breeds, including Arabian, Quarter Horse, Paso Fino, and Trakehner. The disease is incurable, but early detection by genetic testing can help identify male horses that are carriers of the mutation and prevent their further breeding to avoid producing affected horses.
Results Reported As
Test Result |
Interpretation of test result |
Healthy male |
Horse is healthy and does not have the gene with the AIS causing mutation. |
Affected male |
Horse is affected and has one copy of the gene with the AIS causing mutation. |
References:
Kent, M., Shoffner, R., Hunter, A., Elliston, K., Schroder, W., Tolley, E., & Wachtel, S. (1988). XY sex reversal syndrome in the mare: clinical and behavioral studies, H-Y phenotype. Human Genetics, 79(4). doi:10.1007/bf00282169
Neuhauser, S., Handler, J., Schelling, C., & Pieńkowska-Schelling, A. (2018). Disorder of Sexual Development in a Mare with an Unusual Tentative Mosaic Karyotype: 63,X/64,Xdel(Y). Sexual Development. doi:10.1159/000490861