Sex Reversal Syndrome in an Egyptian Arabian Horse Detected Using Genomic Data - A case report.
Authors: Nogueira Pedro Paulo Oliveira, Amorim Gabrielle Bueno de Almeida Gonçalves, Oliveira Odilon Marquez de, Demyda-Peyrás Sebastián, Santos Bruna Mendonça, Mota Lígia Souza Lima Silveira da
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Sex Reversal Syndrome in an Egyptian Arabian Horse A 4-year-old Straight Egyptian Arabian presented with ambiguous external genitalia and stallion-like behaviour despite displaying anatomical features typically associated with female development, prompting investigation into the underlying chromosomal and hormonal basis of this intersex condition. Comprehensive genetic analysis—including karyotyping, short tandem repeat (STR) profiling, and single nucleotide polymorphism (SNP) genotyping—revealed a 64,XX chromosome complement with no numerical aberrations, large deletions, or duplications on autosomes, whilst hormonal assays measured testosterone and oestradiol concentrations. The researchers concluded the horse represented a male pseudohermaphrodite, with the masculinised phenotype and behavioural characteristics occurring despite the expected female karyotype and without evidence of somatic chimerism. For equine practitioners, this case highlights that sex development disorders can occur through mechanisms other than chromosomal mosaicism or numerical abnormalities, likely involving atypical sex hormone signalling or androgen receptor expression during foetal development. Whilst rare, such presentations warrant thorough genetic and endocrine evaluation to inform breeding decisions and manage behavioural and welfare implications in breeding stock.
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Practical Takeaways
- •Sex reversal syndrome should be considered in horses presenting with ambiguous genitalia and incongruent sexual behavior; genomic testing is essential for definitive diagnosis
- •Comprehensive genetic analysis including karyotyping, STR, and SNP genotyping can rule out chromosomal chimerism and identify pseudohermaphroditism cases
- •This condition has significant breeding implications—affected animals should be identified early to prevent inappropriate breeding selections
Key Findings
- •A 4-year-old Egyptian Arabian horse with 64,XX karyotype displayed male phenotype with stallion-like behavior and malformed external genitalia
- •Hormonal analysis and molecular testing (STR and SNP genotyping) confirmed male pseudohermaphroditism without numerical chromosomal aberrations or large deletions/duplications
- •No hematopoietic chimerism was detected and parental chromosomal analysis ruled out inherited numerical abnormalities