ABSTRACT
Abnormalities of sexual development causing infertility in horses have been investigated since the early 1970's. Conventional cytogenetic analysis by karyotyping has been the primary tool used to investigate these horses. Abnormalities have a broad range, from a phenotypically normal mare with gonadal dysgenesis to a horse with ambiguous external genitalia and internal male and female organs. Cytogenetic analysis can determine genetic sex but cannot identify mutations or deletions of genes involved in the sex determination pathway. Molecular technologies have been developed to confirm cytogenetic results and to aid in identifying the genetic causes of abnormal sex determination in horses. In this paper, we review the historical development of methods used to understand abnormal sexual development in the horse as well as summarize cases reported over the last 40-50 years.
Subject(s)
Disorders of Sex Development/veterinary , Horse Diseases , Animals , Disorders of Sex Development/genetics , Female , Horse Diseases/genetics , Horses , Hypospadias/genetics , Hypospadias/veterinary , Karyotyping/veterinary , Male , Mosaicism/veterinary , Mutation , Sex Chromosome Disorders of Sex Development/veterinary , Sex Chromosomes/geneticsABSTRACT
We described the clinical, cytogenetic and molecular findings of 17 clinical equine cases presented for abnormal sexual development and infertility. Six horses with an enlarged clitoris had an XX, SRY-negative genotype, which displayed male-like behavior (adult individuals). Bilateral ovotestes were noted in 2 of those cases, while another case showed increased levels of circulating testosterone. Six horses with a female phenotype, including normal external genitalia, had an XY, SRY-negative genotype. These individuals had small gonads and an underdeveloped internal reproductive tract. Four horses with normal appearing external genitalia had an XY, SRY-positive genotype, 3 of them had hypoplastic testes and male-like behavior. In addition, one young filly with enlarged clitoris and hypoplastic testes had the same genotype but did not show male-like behavior due to her age. Three of these horses were related with 2 being siblings. These findings demonstrate the diversity of disorders of sexual development seen in the horse. Furthermore, they emphasize the need for further research to identify genes involved in abnormal sex determination and differentiation in the horse.
