63,XO/65,XYY mosaicism in a case of equine male pseudohermaphroditism.

This research paper details an instance of a male pseudohermaphrodite Arabian horse with the chromosomal abnormality of 63,XO/65,XYY. The horse, initially identified as a female, displayed physical and behavioral traits akin to that of a stallion which led to a comprehensive chromosomal and histological analysis.

Background of Study

• This research focuses on horses with chromosomal abnormalities and sexual ambiguities—one of which being pseudohermaphroditism, a condition where an animal possesses both male and female sex organs.
• The horse under study was an Arabian breed, initially assumed as female, but later depicted stallion-like sexual behavior which became a cause for concern.
• Clinical examination of the horse revealed abnormalities in the horse’s sexuality with a few distinguishing characteristics such as an enlarged clitoris, an underdeveloped prepuce, and a long and obstructed vulva containing a small penis. However, palpation could not locate the gonads.

Research Procedure

• A blood sample and skin biopsy were taken in order to start cell cultures and perform cytogenetic analyses.
• These cell cultures were examined for chromosomal variations and different cell types.
• At a later stage, the horse was given general anesthesia and its gonads, located in an inguinal position, were removed for histological analysis.

Findings and Conclusion

• The chromosomal analysis revealed the horse to be a carrier of the 63,XO/65,XYY karyotype—two cell types (XO and XYY) were found in each cell culture.
• In both types, the XO cells were significantly dominant: 82.1% in the lymphocyte sample and 98.7% in the fibroblast sample.
• This suggests fundamentally that the horse’s chromosomal abnormality is a combination of 63,XO/65,XYY, leading to its pseudohermaphrodite condition.