Authors: Peretti Vincenzo, Satué Katiuska, Ciotola Francesca, Cristarella Santo, De Majo Massimo, Biondi Vito, D'Anza Emanuele, Albarella Sara, Quartuccio Marco
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary A three-year-old Arabian mare presenting with behavioural abnormalities—including stallion-like aggression and masculine temperament—underwent comprehensive diagnostic evaluation that revealed a rare condition of sex development (DSD). Clinical examination demonstrated an unusually shortened anogenital distance with dorsally fused vulvar lips and a protruding phallic structure; ultrasound confirmed the presence of both uterine tissue (hypoplastic horns, cervix, corpus) and gonadal structures resembling testicular tissue, whilst testosterone levels measured only 0.4–0.6 ng/mL. Crucially, cytogenetic and molecular analysis established a phenotypically female karyotype (64,XX) with absence of the SRY and ZFY genes that typically direct male sex determination, making this the first documented equine case of 64,XX SRY-negative DSD with simultaneous differentiation of both Müllerian-derived (uterus, fallopian tube) and mesonephric (epididymal structures, penile tissue) anatomies. Post-mortem examination confirmed this remarkable mosaic of male and female internal genitalia arising from a single genital ridge, suggesting aberrant gonadal development unrelated to chromosomal sex. For practitioners, this case illustrates that behavioural and morphological signs of sex reversal may reflect complex developmental anomalies rather than straightforward genetic sex determination, emphasising the need for multidisciplinary diagnostic investigation—including cytogenetics and endocrine assessment—when managing reproductive abnormalities with incongruent phenotypic presentation.
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Practical Takeaways
- •Unexplained stallion-like behavior in mares warrants investigation for possible DSD including cytogenetic and endocrine assessment, as this rare condition can occur with normal female karyotype
- •XX SRY-negative DSD in equines may present with ambiguous external genitalia and behavioral abnormalities that could be mistaken for behavioral issues rather than anatomical/endocrine pathology
- •Ultrasound examination combined with cytogenetics and PCR testing for Y chromosome markers is essential for diagnostic confirmation in suspected intersex conditions
Key Findings
- •First reported case in equine species of 46,XX SRY-negative DSD with concurrent male and female genital structures
- •Animal presented with stallion-like behavior (aggressiveness, masculine attitude) despite normal female karyotype (2n=64,XX)
- •Necroscopic findings revealed hypoplastic testicular-like structures, epididymal portions, and penis-like structure alongside functional female internal genitalia (uterus, cervix, salpinx)
- •Testosterone levels were low (0.4-0.6 ng/mL) despite presence of male-type genital tissue