XX male syndrome in a cryptorchid stallion.

The research discusses the case of a stallion with XX male syndrome – a rare genetic disorder – diagnosed via karyotyping, which also exhibited underdevelopment of male sex organs and lack of spermatogonia. Normal hormonal profiles would not have been sufficient to diagnose this syndrome.

Identification of the Syndrome

• The study starts with the identification of a bilateral cryptorchid stallion exhibiting mild mammary gland development. Cryptorchidism is a condition in which one or both of the testes fail to descend. In this stallion’s case, the condition was bilateral (both testes were undescended).
• On noticing the uncharacteristic development of mammary glands, the researchers decided to further investigate this anomaly.

Karyotyping and XX Male Syndrome

• The researchers performed a karyotyping procedure on the stallion. Karyotyping is a process that involves the pairing and numbering of chromosomes in the cell’s nucleus to determine their collection in an individual’s cells. Karyotyping is typically used to diagnose genetic disorders.
• The result of the karyotyping revealed a XX genotype, normally associated with female animals. This was unusual as the individual was a stallion (male horse). Therefore, the researchers concluded that the stallion was suffering from XX Male Syndrome, a rare genetic disorder with a male phenotype but a genetically female genotype.

Necropsy Findings

• To further understand the condition, the researchers performed a necropsy on the stallion. The necropsy revealed underdeveloped accessory sex organs and hypoplastic, inguinally located testes. Hypoplastic describes the underdevelopment or incomplete development of a tissue or organ. This was consistent with the symptoms of XX Male Syndrome, as the disorder often results in abnormal sexual development.
• The necropsy also found that the testes were deficient of spermatogonia – the cells that give rise to sperm. This would have potentially made the stallion infertile.

Limitations of Routine Hormonal Profiles

• Finally, the study points out that routine hormonal profiles would not have been able to diagnose this syndrome. This is likely because XX male syndrome does not typically result in abnormal hormone levels, but rather results in a mismatch between physical characteristics and genetic sex determination.