The use of a novel combination of diagnostic molecular and cytogenetic approaches in horses with sexual karyotype abnormalities: A rare case with an abnormal cellular chimerism

Sex chromosome aberrations are known to cause congenital abnormalities and unexplained infertility in horses. Most of these anomalies remain undiagnosed because of the complexity of the horse karyotype and the lack of specialized laboratories that can perform such diagnoses. On the other hand, the utilization of microsatellite markers is a technique widely spread in horse breeding, mostly because of their usage in parentage tests. We studied the usage of a novel combination of diagnostic approaches in the evaluation of a very uncommon case of chromosomal abnormalities in a Spanish purebred colt, primarily detected using a commercial panel of short tandem repeat (STR) makers. Based on these results, we performed a full cytogenetic analysis using conventional and fluorescent in situ hybridization techniques with individual Equus caballus chromosome X and Equus caballus chromosome Y painting probes. We also tested the presence of two genes associated with the sexual development in horses and an extra novel panel of eight microsatellite markers specifically located in the sex chromosome pair. This is the first case report of a leukocyte chimerism between chromosomally normal (64,XY) and abnormal (63,X0) cell lines in horses. Our results indicate that the use of the short tandem repeat markers as a screening technique and as a confirmation utilizing cytogenetic techniques can be used as a very interesting, easy, and nonexpensive diagnostic approach to detect chromosomal abnormalities in the domestic horse.