The Use of Genomic Screening for the Detection of Chromosomal Abnormalities in the Domestic Horse: Five New Cases of 65,XXY Syndrome in the Pura Raza Español Breed.
Authors: Valera Mercedes, Karlau Ayelén, Anaya Gabriel, Bugno-Poniewierska Monika, Molina Antonio, Encina Ana, Azor Pedro J, Demyda-Peyrás Sebastián
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Chromosomal abnormalities, particularly sex chromosome aneuploidies, represent a significant but often undiagnosed cause of reproductive failure in horses, making robust screening protocols essential for breeding programmes. The Pura Raza Español studbook implemented a tiered genomic approach combining Short Tandem Repeat (STR) parentage testing as an initial screen, followed by confirmatory Single-Nucleotide Polymorphism (SNP)-based copy number aberration analysis on flagged cases, applied across 27,330 foals over two breeding seasons. This methodology identified five individuals with 65,XXY karyotype (equine Klinefelter syndrome)—the largest cohort of such cases reported to date—with one animal displaying abnormal gonad development whilst the remaining four presented normal external reproductive anatomy. These findings underscore that genomic screening can effectively identify chromosomal abnormalities that would otherwise escape clinical detection, particularly given that affected individuals may appear phenotypically normal despite carrying significant reproductive limitations. For breeding professionals, this work reinforces the value of implementing pre-studbook genomic screening, especially in closed or intensively managed populations where such abnormalities might otherwise perpetuate through the gene pool undetected.
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Practical Takeaways
- •Genomic screening should be implemented as routine protocol in breeding programs to identify sex chromosomal abnormalities before animals are enrolled in studbooks, preventing propagation of reproductive failures
- •65,XXY carriers may have normal external reproductive morphology but should be excluded from breeding despite appearing phenotypically normal, as the condition causes reproductive dysfunction
- •Combined STR and SNP-based testing is more effective than phenotypic assessment alone for detecting chromosomal abnormalities; phenotypically normal animals can still carry 65,XXY syndrome
Key Findings
- •Five cases of 65,XXY syndrome identified among 27,330 foals (0.018%) screened in Pura Raza Español breed using combined STR and SNP-based genomic screening
- •This represents the largest reported cohort of horses with equine Klinefelter syndrome (65,XXY) to date
- •Four of five cases exhibited normal reproductive morphology despite chromosomal abnormality; one case showed abnormal gonad development
- •Routine genomic screening combining STR parentage testing with SNP-based copy number analysis effectively identifies sex chromosomal abnormalities for breeding program management