SRY negative 64,XX intersex phenotype in an American saddlebred horse.
Authors: Bannasch D, Rinaldo C, Millon L, Latson K, Spangler T, Hubberty S, Galuppo L, Lowenstine L
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary A clinically normal-appearing American saddlebred mare presented with masculinised external genitalia and stallion-like behaviour, prompting investigation of a suspected intersex condition. Laparoscopic examination revealed absent reproductive organs typical of females, but hypoplastic testicular-like tissue was identified and surgically removed; histological analysis confirmed the absence of functional spermatogonia. Genetic analysis proved surprising: chromosomal karyotyping demonstrated a normal female complement (64,XX), and polymerase chain reaction testing for the SRY (sex-determining region Y) gene returned negative in both peripheral blood and the testicular tissue—making this the first documented case of SRY-negative XX sex reversal in equines. This unusual presentation suggests a novel genetic mechanism of sex reversal independent of the classical SRY-mediated pathway, potentially inherited, that may occasionally present in the breed. Practitioners encountering horses with intersex phenotypes should recognise that chromosomal and molecular testing may reveal unexpected results; this case warrants heightened awareness among breeders regarding potential hereditary factors in the American saddlebred population.
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Practical Takeaways
- •Intersex conditions in horses may present with ambiguous external genitalia and atypical sexual behaviour; genetic testing is necessary for accurate diagnosis beyond physical examination
- •SRY-negative XX sex reversal represents a potentially heritable condition in certain horse breeds, warranting pedigree consideration and breeding decisions
- •Laparoscopic examination combined with histopathology and genetic testing provides definitive diagnosis for cryptic intersex conditions in equine patients
Key Findings
- •First documented case of SRY-negative XX-male sex reversal intersex phenotype in American saddlebred horse
- •Horse exhibited 64,XX karyotype (genetically female) with stallion-like behaviour and abnormal external genitalia
- •Testicular-like tissue removed during laparoscopy contained no spermatogonia on histopathology
- •Polymerase chain reaction confirmed absence of SRY gene in both peripheral blood and testicular-like tissue