64, XX, SRY-negative, testicular DSD syndrome in a Lusitano horse.

The research article discusses a unique case of sex development disorder in a Lusitano horse breed from Portugal which possessed mixed characteristics of both female and male genitalia but lacked the gene known to be responsible for testes formation.

Study Overview

• The research focused on a sex development disorder observed in a horse of the Portuguese Lusitano breed. This condition led to the presence of uncharacteristic sexual traits both in genitalia and behavior.
• This horse exhibited a peculiar genital phenotype that included structures usually seen in female horses such as mammary glands and hypoplastic uterine horns. Simultaneously, it also had abdominal testes without its associated duct, epididymis, and a penis-like structure, traits typically seen in male horses.
• The penis-like structure was in a reversed position but functioned for micturition and erection. The horse showed a female position when urinating and exhibited male-like aggressive behavior, including specific mating actions like mounting and flagging of the tail.

Genetic Evaluation and Hormonal Profile

• The researchers conducted a genetic evaluation which indicated that the horse had an XX karyotype, typically associated with female sexual development, and was SRY-negative. The SRY gene is generally responsible for triggering male sexual development, and its absence is unusual in a subject showing male gonadal characteristics like testes.
• In addition, hormonal analysis showed that the horse had testosterone concentrations below detection limits, a result discordant with the presence of testes and certain male-type behaviors.

Interventions and Suggestions for Future Research

• Due to their abnormality, abdominal gonads were surgically removed. The penis was amputated, and the urethra repositioned.
• This situation, where the chromosomal sex (XX, usually associated with female) and gonadal sex (in this case, testes, usually associated with male) do not match, suggests that testes can develop even in the absence of the SRY gene.
• The researchers suggest further investigation into other genetic and cellular pathways responsible for gonad differentiation, indicating that our understanding of sexual development might be more complex than currently known.