An equine intersex with unilateral gonadal agenesis.

This research focuses on a unique case of an intersex horse, which exhibited unusual characteristics and chromosome types. The horse, initially thought to be a cryptorchid, had both male and female physical traits and was shown to be quadruple mosaics through chromosome analysis. The findings suggest that the horse may have developed from an XXY zygote, with multiple cell types originating from different mitotic mechanisms during embryonic development.

Clinical Condition and Physical Characteristics

• The subject of the study is an intersex horse that was initially diagnosed as a cryptorchid, a condition where one or both of the testes fail to descend.
• The horse possessed physical characteristics of both sexes, including a well-developed vulva and a penis, taking the general conformation of a stallion.
• The right testis, which had descended, was devoid of germ cells, while the left gonad, located in the cavum vaginale, contained neither testicular nor ovarian tissue.
• Even without a testis on the left side, the male duct system on both sides were quite developed.

Chromosomal Analysis and Findings

• The researchers conducted chromosome analysis on cultured cells taken from the descended right testis, which revealed a quadruple mosaicism, a condition where an individual has more than one genetically distinct type of cells in their body.
• The horse had four chromosomally distinct cell types with XX, XY, XXY, and XO sex complements. XX and XY are female and male, respectively, while XXY and XO are both types of intersex conditions in mammals.

Interpretations and Possible Origin

• The researchers found the presence of polymorphonuclear neutrophils showing a drumstick-like appearance in the horse’s hemopoietic tissues, along with a sex chromatin body in the cells of the buccal mucosa. These findings suggest that mosaicism is present in other somatic tissues of the horse.
• The consensus, considering similar conditions observed in humans and other animals, is that the horse might have developed from an XXY zygote. The four distinct cell types noted could have resulted from mitotic mechanisms that favored the loss of X and Y chromosomes at different stages during embryonic development.
• The absence of a gonad on the left side of the horse could be linked to the predominance of XO cell types in the somatic blastema during early gonadal differential.