CONICET | Buscador de Institutos y Recursos Humanos

Sex reversal syndrome is a genetic disorder in the horse associated with morphological abnormalities in the reproductive tract and infertility.The most common presentation is the 64,XY-SRY-negative DSD, i.e., animals present a male chromosomal complement (64,XY)but they are morphologically characterized as females. These individuals always show the absence of a functional SRY (sex-determining region) gene located on the Y chromosome (ECAY). The only previous comprehensive study described two possibilities: a massive ECAY deletion (two cases), or a 21-kb deletion surrounding the SRY region(11 cases) (Raudsepp et al. 2010). Here we present preliminary results of two cases evidencing a new larger deletion which has not been described earlier. Two phenotypic mares showing classic symptoms of sex reversal syndrome (sterility, small or hypoplastic ovaries and uterus and absence of sexual behavior or cyclicity in the breeding season) were studied. The absence of the SRY gene was determined by PCR. A further characterization of the SRY-surrounding region was performed by genome walking, using eleven newly designed primer pairs, covering a region of approximately 35 extra kb. Based on the combination of fragments amplified, it was determined that this deletion fell into a size ranging between 38.7 and 41.9 kb and was at least 15 kb larger than previously reported. Despite the fact that molecular differences with previous studies are remarkable, the reproductive morphology and behavior of the studied animals were similar. Theseresults strongly suggest that the sole inactivation of the SRY gene is enough to produce the disorder, but also confirm certain variability in the deletion associated to this reproductive disease in horses.