XX male pseudohermaphroditism in a horse.

This research article discusses the study of a pseudohermaphrodite horse that exhibited aggressive stallion behavior and had ambiguous external genitals. The horse, which was discovered to have underdeveloped testes inside its abdomen and a 64,XX chromosomal pattern, was neutered.

Underlying Testes in a Pseudohermaphrodite Horse

• The horse in the study was identified as a pseudohermaphrodite, a condition wherein an individual possesses the physical traits of one sex but the reproductive organs of the other sex.
• In this case, the horse exhibited aggressive behavior typically associated with stallions but had ambiguous external genitalia. The ambiguity of the external genitalia suggested the presence of two sex physical traits, leading to the pseudohermaphroditism diagnosis.
• The horse was subjected to a gonadectomy procedure, through which it was discovered that the horse had hypoplastic testes inside its abdomen. Hypoplastic refers to the underdevelopment or incomplete development of an organ. So, in this case, the horse’s testes were not fully developed and were situated inside the abdomen instead of the scrotum.

64,XX Karyotype in a Male Horse

• Additional testing of the horse’s blood and fibroblasts – cellular components responsible for healing and tissue restoration – revealed a 64,XX chromosomal type.
• A karyotype represents the number and appearance of chromosomes in the nucleus of a eukaryotic cell. In mammals, the XX karyotype typically denotes genetic femininity; however, this horse exhibited male characteristics and had testes, making it an unusual case.
• This suggests a form of XX male syndrome, also known as de la Chapelle syndrome, where an individual genetically has two X chromosomes but is phenotypically male. This condition is considered a rare form of sex reversal that does not affect fertility but leads to intra-abdominal testes, as seen in this horse.