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→ Infertility and external female genitalia in male horses

Symptoms:

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

General Information:

  • Affected foals appear like normal females.
  • Underdeveloped male and female genitalia result in infertility.
  • Retained testes 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.

Inheritance: X-chromosomal recessive

→ The affected gene is located on the X-chromosome. Females have two versions of this chromosome while males only have one. Males with this variant are affected by AIS. Females can be carriers of this variant (heterozygous, X/Xais).

Possible Genotypes:

Genotype The horse is:
Effects:
X/X a normal female. The mare has no genetic variant causative for the AIS and therefore cannot pass it on to its offspring.
X/Xais 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.

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Recommendations:

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

Test information: This test detects the single basepair change in the AR gene.

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 is available at Online Mendelian Inheritance in Animals.

Breeds affected

Quarter Horse and related breeds

Test #: H113

Samples: Blood, Hair

Price: 35 € (net)

Time required: 7-10 days

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