A case of ambiguous external genitalia in a Thoroughbred male horse with the 63,XO/64,XY mosaic karyotype.

The research discusses a Thoroughbred colt (a young male horse in this context) exhibiting ambiguous external genitalia and its subsequent clinical and histological examination. The study adds to existing knowledge on chromosomal abnormality and genital disorders in horses.

Background

The study focuses on a Thoroughbred colt who showed signs of abnormal genital formation, characterized by a backward-facing short penis. To gain a comprehensive understanding of this atypical condition, both clinical and histological examinations were carried out.

Research Methodology

• Hormone Measurements: The researchers conducted several measurements of different hormones – luteinizing, follicle-stimulating, testosterone, and ir-inhibin. They observed a gradual increase in these hormones from April.
• Genetic Testing: The research team implemented the Polymerase Chain Reaction (PCR) method to detect any genetic irregularities, particularly aiming to detect the sex-determining region of the Y chromosome and amelogenin gene fragments.
• Cytogenetic Analysis: This provided an in-depth look into the chromosomal configuration of the horse, revealing a 63,XO/64,XY mosaic karyotype. Mosaic karyotype refers to the state when some cells in an organism differ in their genetic constitution. In this case, the ratio being 83:17, indicating that 83% of cells had a 63,XO constitution, and 17% had a 64,XY constitution.

Findings and Conclusion

After the horse’s death, an autopsy was performed; immature symmetrical subcutaneous testes were found in the inguinal regions. Upon further examination, the team discovered that both the testes and other accessory sex organs were histologically normal, indicating that the abnormality did not result from structural defects in these organs.

The colt’s ambiguous external genitalia condition is tied to its unusual chromosomal constitution, revealing a rare occurrence of chromosomal abnormality. This study contributes to the broader understanding of chromosomal disorders and sex development issues in horses.