Numerical sex chromosome aberrations and abnormal sex development in horse and sheep.

The research article explores two cases of abnormal sexual development in animals, one horse and one sheep, both associated with irregularities in the number of sex chromosomes.

Case Study: Standardbred Filly

• The researchers examine a 17-month-old Standardbred filly, which was sent to an equine fertility center as a potential embryo donor because it was noticeably smaller than a typical racehorse of the same age.
• The horse’s external genitalia appeared normal, but manual palpation of the reproductive tract revealed underdevelopment of the uterus and ovaries.
• This underdevelopment was confirmed through an ultrasonographic examination.
• The researchers conducted a cytogenetic investigation using CBA-banding, which is a technique used to observe chromosomal structures.
• This investigation revealed an abnormal karyotype, or arrangement of chromosomes, with a X chromosome monosomy. This means that the horse had only one copy of the X chromosome instead of the usual two, leading to its total chromosome count to be 63 instead of the normal 64.

Case Study: 18-Month-Old Ewe

• The research also included a case study of an 18-month-old ewe that displayed distinct heterosexual traits, including a vulva with an enlarged clitoris, well-developed abdominal testes, and mammary glands.
• Despite these external traits, the ewe’s internal sex adducts, or reproductive organs, were atrophic, meaning they had degenerated or wasted away. This was observed following mating.
• A cytogenetic analysis revealed the presence of XX/XY mosaicism. This is a condition where some cells in the body have two X chromosomes (typical of females) and other cells have one X and one Y chromosome (typical of males).
• This abnormal sex chromosome arrangement leads to a range of developmental abnormalities, including the mixed external and internal traits seen in this ewe.

Conclusion

• The research presented by the authors of this study highlights the sex chromosome aberrations as potential causes for abnormal sex development in animals.
• The case studies presented here contribute to an understanding of the range of conditions and cases that can result from these genetic irregularities.