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Androgen Insensitivity Syndrome (AIS)


→ Infertility and external female genitalia in male horses.

Instructions for ordering:

  1. Enter the information of the first horse for which you want to order the test
  2. Add to cart
  3. Go to cart to check out, or
  4. Enter the information for a second horse
  5. For sample collection follow the instructions here.
  6. You can use this template to send in hair samples.
  7. Please also send the completed order form together with the samples.

For a breeder or veterinarian discount please contact us before ordering.

Any information you include here is optional, but will be included on the certificate of results (except “Additional Info”).

Enter the name of your animal
Enter your animal's date/year of birth
Enter the breed name
Enter the registration number if known
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Is there anything else you would like to tell us about your horse? Reason for testing, symptoms etc.?

General Information

  • Affected foals appear like normal females.
  • Underdeveloped male and female genitalia result in infertility.
  • Retained testicles are usually surgically removed.
  • A malfunction of androgen receptor (male steroid hormone) causes the syndrome.
  • No other effects on health of affected horses are known.


  • Affected horses (genotypic males) have external female genitalia.
  • Underdeveloped uterus and underdeveloped, retained testes
  • Infertility
  • Stereotypically male-like behavior

Inheritance and Genotypes

→ AIS is an X-chromosomal recessive disease, meaning that females with one copy of the genetic variant (Xais/X) are clinically normal carriers while males with one copy of the genetic variant (Xais/Y) are affected.

Genotype: The horse is: Effects:
X/X a normal mare. The horse does not have any copies of the genetic variant causative for AIS and therefore cannot pass it on to any offspring.
Xais/X a carrier female. The mare is clinically healthy. The genetic variant will be passed on to its offspring with a probability of 50%. If the variant is passed on to male offspring, the foal will be an affected male.
X/Y a normal male. The male has no genetic variant causative for the AIS.
Xais/Y an affected male. The male appears to be a normal female but has the male genotype (XY) and is infertile.


  • Offspring of a carrier female should be tested for their genotype (X/X or Xais/X or Xais/Y → affected male).
  • Carrier females (Xais/X) may be used for breeding but their male offspring have a 50% of being affected.
  • Affected males are infertile but otherwise healthy.


Révay, T., Villagómez, D.A., Brewer, D., Chenier, T., King, W.A.: GTG mutation in the start codon of the androgen receptor gene in a family of horses with 64,XY disorder of sex development. Sex Dev 6:108-16, 2012. Pubmed reference: 22095250. DOI: 10.1159/000334049.

Further information are available at Online Mendelian Inheritance in Animals.

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