Prevalence of Sex-Related Chromosomal Abnormalities in a Large Cohort of Spanish Purebred Horses.
Authors: Demyda-Peyrás Sebastián, Laseca Nora, Anaya Gabriel, Kij-Mitka Barbara, Molina Antonio, Karlau Ayelén, Valera Mercedes
Journal: Animals : an open access journal from MDPI
Summary
Sex-linked chromosomal abnormalities pose a significant threat to breeding programmes, yet their true prevalence in horse populations remains poorly defined; this research screened 25,237 Pura Raza Español horses using a two-stage molecular approach combining short tandem repeat (STR) parentage testing with SNP-based diagnostics to quantify the occurrence of cytogenetic disorders. Thirteen animals (0.05% prevalence) were identified as chromosomally abnormal, comprising five 64,XY mares with sex development disorders, four blood chimerism cases (two with male/female and two with female/female combinations), two complex karyotypes, one Klinefelter and one Turner syndrome case. The 64,XY disorder of sex development (DSD) and blood chimerism prevalence rates of 0.02% and 0.016% respectively are particularly relevant, given that affected mares are frequently presented for infertility workup despite being phenotypically female, creating diagnostic and counselling challenges for practitioners. The authors acknowledge a significant methodological limitation: Turner syndrome carriers (particularly mosaic forms) cannot be reliably detected with their screening approach, suggesting the true prevalence figure is likely underestimated. For practitioners managing breeding stock or investigating unexplained subfertility in mares, these findings underscore the value of molecular cytogenetic testing in high-value individuals and the importance of maintaining updated pedigree records, particularly where anomalous reproductive histories cluster within families.
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Practical Takeaways
- •Chromosomal abnormalities are rare (~0.05%) but clinically significant in horses presenting with unexplained infertility or sex development disorders; molecular screening should be considered in relevant cases
- •Identify mares with virilization or developmental abnormalities and stallions with poor fertility as candidates for chromosomal testing, as this may reveal 64,XY DSD or blood chimerism
- •SNP-based testing is more reliable than traditional karyotyping for detecting chromosomal abnormalities in breeding populations and should be prioritized for accurate diagnosis
Key Findings
- •Overall prevalence of chromosomal abnormalities in 25,237 Pura Raza Español horses was ~0.05% (13 individuals)
- •Sex development disorders (64,XY mares) occurred in ~0.02% of population (5 cases), and blood chimerism in ~0.016% (4 cases)
- •Detected one Turner syndrome case, one Klinefelter syndrome case, and two individuals with complex karyotypes
- •SNP-based molecular methodology successfully diagnosed all 13 screened positive cases, though Turner syndrome carriers may be underdetected due to methodological limitations