Molecular cytogenetic screening of sex chromosome abnormalities in young horse populations

Abstract

BackgroundChromosomal abnormalities occur in the equine population at a rate of approximately 2%. The use of molecular cytogenetic techniques allows a more accurate identification of chromosomal abnormalities, especially those with a low rate of abnormal metaphases, demonstrating that the actual incidence in equine populations is higher.ObjectivesEstimation of the number of carriers of karyotypic abnormalities in a sample from a population of young horses of various breeds, using molecular cytogenetic techniques.Study designCross‐sectional.MethodsVenous blood samples were collected from 500 young horses representing 5 breeds (Purebred Arabian, Hucul, Polish primitive horse [Konik], Małopolska, Coldblood, Silesian). Chromosomes and DNA were obtained from blood lymphocytes and evaluated by fluorescence in situ hybridisation (FISH) and PCR, using probes and markers for the sex chromosomes and select autosomes.ResultsNineteen horses, 18 mares and 1 stallion, were diagnosed with different chromosomal abnormalities: 17 cases of mosaic forms of sex chromosome aneuploidies with a very low incidence (0.6%–4.7%), one case of a SRY‐negative 64,XY sex reversal mare, and one mare with X‐autosome translocation. The percentage of sex chromosomal aberrations was established as 3.8% in the whole population, 6.08% in females and 0.49% in males.Main limitationsLimited sample size, confined to horses from Poland.ConclusionsThe rate of sex chromosomal abnormalities we identified was almost double that reported in previous population studies that used classical chromosome staining techniques. FISH allowed the detection of aneuploid cell lines which had a very low incidence. The FISH technique is a faster and more precise method for karyotype examination; however, it is usually focused on only one or two chromosomes while banding karyotyping includes the entire chromosome set.

Advances in equine reproduction

“…Bugno-Poniewierska et al 18 describe the use of fluorescent in situ hybridisation (FISH) to improve the reliability of detecting karyotypic abnormalities in live horses; they detected sex chromosome abnormalities, including monosomies, trisomies and deletions or fissions of the chromosome arms, in 19 of 500 horses (6.08% and 0.49% of female and male horses examined, respectively). FISH was invaluable in establishing the diagnosis because, in 17 of the 19 cases, the affected animals were indeed mosaic, and in some cases only a small proportion of cells carried the abnormality; these affected cells could easily have been missed by conventional karyotypic analysis.…”