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farriery
veterinary
biomechanics
anatomy
nutrition
physiotherapy
2020
Case Report

Application of droplet digital PCR in diagnosing of X monosomy in mares.

Authors: Szczerbal Izabela, Nowacka-Woszuk Joanna, Kopp-Kuhlman Christine, Mackowski Mariusz, Switonski Marek

Journal: Equine veterinary journal

Summary

# Editorial Summary: Droplet Digital PCR for Diagnosing X Monosomy in Mares X monosomy remains the most common chromosomal disorder of sex development in mares, yet traditional cytogenetic diagnosis is labour-intensive and time-consuming; this study evaluated whether droplet digital PCR (ddPCR)—a more rapid molecular technique—could reliably detect abnormal X chromosome numbers in affected animals. The researchers employed ddPCR to quantify AMELX gene copy number as a proxy for X chromosome copy number, tested this approach against standard fluorescent in situ hybridisation (FISH) in an infertile mare with suspected X monosomy, and validated findings across 70 additional mares using X-linked microsatellite markers and Y-chromosome SRY gene screening. Results showed perfect concordance between ddPCR and FISH in identifying pure X monosomy (single X chromosome confirmed), with two further cases of X monosomy detected among the validation group; critically, ddPCR cannot reliably distinguish mosaic karyotypes (63,X/64,XX or similar), though abnormal results (threshold values <1.8 or >2.2 X copies) can effectively flag cases requiring confirmatory cytogenetic analysis. For practitioners managing infertile mares with suspected chromosomal abnormalities, ddPCR offers a faster preliminary screening tool that could streamline diagnostic pathways and help rule out other causes of sex development disorders (freemartinism, XX sex reversal), though definitive diagnosis of mosaic conditions still demands traditional karyotyping.

Read the full abstract on PubMed

Practical Takeaways

  • ddPCR offers a rapid, reliable molecular screening tool for X monosomy in mares presenting with infertility, reducing reliance on cytogenetics alone
  • If ddPCR results show X chromosome copy numbers <1.8 or >2.2, follow up with traditional cytogenetic analysis to rule out mosaicism
  • This technique enables efficient identification of sex chromosome abnormalities in breeding mare evaluations without requiring full karyotyping as initial step

Key Findings

  • ddPCR successfully detected X monosomy in an infertile mare with concordant results to cytogenetic FISH analysis
  • Of 70 additional mares screened, 2 cases of single X chromosome copy were identified via ddPCR
  • ddPCR cannot definitively identify mosaic forms of X chromosome abnormalities but can prompt further cytogenetic investigation
  • ddPCR showed 100% concordance with cytogenetic analysis for non-mosaic X monosomy detection using AMELX gene copy number estimation

Conditions Studied

x monosomydisorder of sex developmentinfertility in mares