Sex reversal syndrome (64,XY; SRY-positive) in a mare demonstrating masculine behaviour.

This research article discusses a case involving a Thoroughbred mare that exhibited masculine behavior, infertility, and had a male chromosome configuration. The article suggests that this unique scenario could be an example of androgen insensitivity syndrome.

Case Overview

• The research focuses on a 5-year-old Thoroughbred mare that was displaying masculine behaviors and struggling with infertility.
• Cytogenetic and molecular analyses were conducted to understand the peculiarities of the case.

Cytogenetic and Molecular Analysis

• Chromosome studies of the mare, including painting with the whole X chromosome specific probe, unveiled a male chromosome complement, specifically 64, XY configuration. Usually, a female horse would have a 64, XX configuration.
• Polymerase Chain Reaction (PCR) amplification was carried out for the SRY and ZFY genes, which usually determine the sex of an individual. In this case, both genes were present.
• An endocrinological study was also conducted which revealed a high level of testosterone (9.7 nmol/l), typically found in male subjects.

Sequencing of the SRY Gene

• Sequencing of the SRY gene, including 5′-UTRs and 3′-UTRs, showed no differences when compared with the sequence of normal stallions (male horses).
• As a result, Basing on the SRY gene, the mare should have been male, but her physical appearance and internal anatomy were female.

Suggested Condition

• All the data from the molecular and cytogenetic analysis, together with the high testosterone level, led the researchers to suggest this mare’s condition as the Androgen Insensitivity Syndrome (AIS), also mentioned as Testicular Feminization Syndrome.
• This syndrome occurs when a genetic male is resistant to androgens (male hormones), hence the body may partially or entirely develop as female despite having a male genetic configuration.