Elevated testosterone levels in a racing horse due to an XY testicular disorder of sexual development.

The article reports on a female horse, successful in racing, that was found to have elevated testosterone levels due to a genetic disorder known as XY testicular disorder of sexual development, caused by complete androgen insensitivity syndrome. This was the first such case to be identified in a thoroughbred racing horse.

Background

• This research focuses on a case of a successful thoroughbred racing horse suspected of having high testosterone levels.
• The horse in question was a female and did not exhibit any stallion-like behaviors or signs of ambiguous external genitalia, typically associated with high testosterone levels.
• Despite its female phenotype, hormone testing showed testosterone values typical of male horses.

Methods and Findings

• The researchers conducted a detailed examination, including tests on the horse’s phenotype, ultrasonographic examination, hormone status, cytogenetic evaluation and molecular diagnostics.
• They determined the horse’s karyotype was 2n = 64,XY and the sex-determining region of the Y chromosome (SRY) PCR was positive. This suggested genetic abnormality in sex determination—it carried male chromosomal makeup (XY), yet functioned as a female horse.
• The tests for eight synthetic testosterone esters were negative, which suggested the increased level of testosterone was naturally occurring and not due to external influences or interventions.
• The results led to the diagnosis of an XY testicular disorder of sexual development (DSD) caused by a complete androgen insensitivity syndrome.

Implications

• This case is unique as it might be the first reported instance of a thoroughbred racing horse diagnosed with an XY testicular disorder of sexual development.
• No regulations are currently in place for intersex racing horses, which presents a new challenge in the regulation and management of horse racing sports, as intersex horses may have a competitive advantage due to elevated testosterone.
• Greater awareness and understanding of this condition will be needed in the horse racing industry to ensure fair competition.