X trisomy in a sterile mare.
Authors: de Lorenzi L, Molteni L, Zannotti M, Galli C, Parma P
Journal: Equine veterinary journal
Summary
A 10-year-old sterile mare underwent chromosomal analysis using C-banding and fluorescence in situ hybridisation to identify the cause of her infertility, revealing a complete X trisomy (2n = 65, XXX) rather than the normal 64 chromosomes with two X chromosomes. Unlike some other chromosomal abnormalities in horses, this mare exhibited no obvious physical or morphological defects beyond reproductive failure, suggesting that X trisomy specifically targets gonadal function without systemic developmental consequences. The cytogenetic findings demonstrate that X trisomy, though exceptionally rare in equine populations, consistently results in infertility, likely due to meiotic abnormalities that prevent normal oogenesis and gamete production. For veterinary practitioners investigating infertility in mares with otherwise normal clinical and behavioural presentation, this case illustrates the value of karyotyping as a diagnostic tool, particularly when conventional reproductive examinations prove unremarkable. Understanding that chromosomal abnormalities can present as isolated infertility without visible congenital features may prevent unnecessary prolonged breeding attempts or complex therapeutic interventions in affected animals.
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Practical Takeaways
- •Consider cytogenetic analysis (C-banding and FISH techniques) for mares with unexplained infertility, as rare chromosomal abnormalities like X trisomy may be causative
- •X trisomy does not produce obvious physical or behavioral signs, so diagnosis requires genetic testing rather than clinical observation alone
- •Affected mares cannot be treated and should be excluded from breeding programs once diagnosis is confirmed
Key Findings
- •A sterile mare presented with 2n = 65, XXX karyotype with no mosaicism detected
- •X trisomy in horses is rare but associated with infertility in mares
- •No other clearly visible phenotypic features were associated with the XXX condition beyond sterility