A case of non-mosaic X trisomy (65,XXX) in a Thoroughbred mare confirmed by cytogenetic and molecular analysis.

This research discusses a unique medical case of a Thoroughbred mare with a rare genetic condition known as non-mosaic X trisomy (65,XXX). The study emphasizes on the importance of detailed gynecological and genetic evaluations of broodmares even when no abnormalities are observed with the naked eye.

Clinical Examination and Diagnosis

• A 9-year-old Thoroughbred mare, showing typical external features and regular oestrus (reproduction cycle) symptoms, was medically examined before insemination.
• Initial discoveries from the examination surfaced underlying abnormalities in the mare’s reproductive organs, including a significantly underdeveloped uterus and absent normal ovaries.
• This led to a more comprehensive set of tests including endocrine (hormonal), genetic, and clinical diagnostics.

Diagnostic Imaging and Hormonal Analysis

• Diagnostic imaging tools, such as ultrasonography (an imaging method that uses sound waves to produce images of structures within the body) and endoscopy (a process where an endoscope is inserted into the body to observe organs), were used to ascertain the underveloped condition of the mare’s internal reproductive organs.
• A hormonal analysis was performed on the mare’s circulating sex hormones. It was observed that the mare had considerably low levels of progesterone and oestradiol, hormones essential for normal reproductive function in mares.

Detection and Confirmation of Genetic Abnormality

• The cytogenetic analysis, a test that visualizes chromosomes to study their structure and number, showed a rare genetic condition of non-mosaic X trisomy (65,XXX). This condition, also known as an aneuploidy of sex chromosomes, is seldom found in horses.
• The diagnosis was further confirmed through molecular methods like droplet digital PCR (ddPCR), a technique used for precise quantification of targeted genetic material, and genotyping of microsatellite markers (genetic markers used for various applications in genetics and genetic engineering).

Conclusion

• The study concludes that, irrespective of the phenotypic characteristics of broodmares (i.e., physical characteristics like developed external genitalia and oestrus symptoms), a thorough gynaecological and genetic evaluation is crucial due to the potential for hidden genetic abnormalities.