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Home / Equine Research Bank / Animals (Basel) / Two Cases of Chromosome 27 Trisomy in Horses Detected Using ...
Animals : an open access journal from MDPI2025; 15(13); 1842; doi: 10.3390/ani15131842

Two Cases of Chromosome 27 Trisomy in Horses Detected Using Illumina BeadChip Genotyping.

Abstract: Autosomal trisomy, a genetic disorder characterized by the presence of an extra autosome, is a rare but important chromosomal abnormality in horses, often associated with infertility, developmental abnormalities, and reduced life expectancy. This study represents the largest population-level screening for autosomal trisomy in horses; the analysis used single nucleotide polymorphism (SNP) panel genotype intensity data from 17,078 horses, 6601 of which were juveniles (i.e., ≤12 months of age) when genotyped. Using methodologies adapted from similar screening studies in cattle, the only aneuploidy detected was trisomy 27 in two juvenile male Irish Sport Horses (ISH) (0.03% prevalence among juveniles or 0.01% prevalence in the overall population). One ISH colt was cytogenetically confirmed and displayed no overt external phenotypic abnormalities, while cytogenetics was not undertaken on the other ISH colt, nor was it phenotypically assessed. Parentage analysis revealed that one ISH colt inherited two different copies of chr27 from the sire, demonstrating heterodisomy, likely due to a nondisjunction event during meiosis I in the sire. The other ISH colt inherited two different copies of chr27 from the dam, also indicating heterodisomy; the dam was 23 years of age when the colt was born. Based on the observed prevalence of autosomal trisomy, it can be estimated that at least 3 foals per 10,000 live births are likely to have autosomal trisomy. Though, given that only 74 (i.e., 0.004%) of horses were genotyped within a month of birth, this is likely an underestimate. The economic consequence of undiagnosed trisomy in high-value breeding horses that are potentially infertile could be substantial. As horse genotyping for parentage verification and discovery is transitioning to medium-density single nucleotide polymorphism panels, routine genomic screening for autosomal aneuploidy could be readily undertaken and potentially should form a standard screening prerequisite along with other genetic defects at horse sales. Currently, thoroughbred horses registered for racing are not genotyped, and only a limited number of sport horse studbooks are using SNP genotyping. This highlights an opportunity for those already genotyping to expand their support for breeders through low-cost, high-value chromosomal screening at the time of registration rather than incurring additional costs over the horse's life cycle to determine the root cause of certain phenotypes owing to the undiagnosed trisomy.
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Publication Date: 2025-06-22 PubMed ID: 40646741PubMed Central: PMC12248643DOI: 10.3390/ani15131842Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study examined the genetic makeup of horses, discovering two instances of trisomy 27, a genetic abnormality, in young Irish Sport Horses. Trisomy typically leads to problems like infertility, development issues, and shorter lifespans. The researchers suggest that routine genomic screening could help identify such abnormalities at an early stage, potentially saving breeders significant costs down the line.

Scope and Methodology

  • The study involved the largest ever population-level screening for autosomal trisomy in horses. The researchers used genotype intensity data from single nucleotide polymorphism (SNP) panels from 17,078 horses, including 6601 juveniles (those aged 12 months or younger).
  • This approach was adapted from similar studies conducted on cattle. The aim was to identify any instances of aneuploidy, a condition of having an abnormal number of chromosomes.

Findings

  • The screening found instances of trisomy 27 in two male juvenile Irish Sport Horses (ISH), demonstrating a prevalence of 0.03% within the juvenile population or 0.01% within the overall horse population.
  • Although no external phenotypic abnormalities were visible in one of these horses, cytogenetic confirmation was achieved. For the other colt, neither cytogenetics nor phenotypic assessment was performed.
  • Parentage analysis revealed that both colts had inherited two different copies of chromosome 27, indicating heterodisomy, most likely due to a non-disjunction event during meiosis I in the parents.
  • Based on these findings, it was estimated that at least 3 out of every 10,000 live horse births could potentially have autosomal trisomy.

Implications and Future Directions

  • The researchers argue that due to the potentially adverse consequences of trisomy, such as infertility, there could be a significant economic impact if it goes undiagnosed in high-value breeding horses.
  • As genotyping for parentage verification and discovery transitions to medium-density SNP panels, routine screening for such chromosomal abnormalities could become easier and potentially could form part of the standard screening process.
  • Currently, thoroughbred horses intended for racing and only a limited number of sport horse studbooks are using SNP genotyping. The scientists see an opportunity for those already genotyping to provide additional value to breeders through low-cost chromosomal screening at registration, instead of facing potentially significant costs later on due to undiagnosed trisomy.

Cite This Article

APA
Ryan CA, Berry DP, Bugno-Poniewierska M, Burke MK, Raudsepp T, Egan S, Doyle JL. (2025). Two Cases of Chromosome 27 Trisomy in Horses Detected Using Illumina BeadChip Genotyping. Animals (Basel), 15(13), 1842. https://doi.org/10.3390/ani15131842

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 13
PII: 1842

Researcher Affiliations

Ryan, Cliona A
  • Teagasc, Moorepark, Fermoy, P61 P302 Co. Cork, Ireland.
Berry, Donagh P
  • Teagasc, Moorepark, Fermoy, P61 P302 Co. Cork, Ireland.
Bugno-Poniewierska, Monika
  • Department of Animal Reproduction, Anatomy and Genomics, University of Agriculture in Krakow, Mickiewicza 24/28 Av., 30-059 Kraków, Poland.
Burke, Mary-Kate
  • Department of Veterinary Medicine, School of Science and Computing, SETU, X91 CF21 Co. Waterford, Ireland.
Raudsepp, Terje
  • Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77840, USA.
Egan, Sonja
  • Horse Sport Ireland, Beech House, Millennium Park, Naas, W91 TK7N Co. Kildare, Ireland.
Doyle, Jennifer L
  • Horse Sport Ireland, Beech House, Millennium Park, Naas, W91 TK7N Co. Kildare, Ireland.

Grant Funding

  • 21/RC/10303_P2 (VistaMilk) / Department of Agriculture

Conflict of Interest Statement

Authors Sonja Egan and Jennifer Doyle were employed by the company Horse Sport Ireland. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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