50,XY gonadal dysgenesis (Swyer's syndrome) in a female river buffalo (Bubalus bubalis)

Sex determination in mammals occurs during fertilisation. Generally, the presence of the Y chromosome gives rise to male sex (or male offspring), even when more than one X is present. In human beings, the term '2n=46,XY gonadal dysgenesis (Swyer's syndrome)' is characterised by a 46,XY karyotvpe and incomplete testicular determinations. The lack of a medullary zone in the non-differentiated gonads affects the formation of testicles even when the Y chromosome is present. Many studies have revealed that this sex reversal may be the result of mutations in some Y-specific genes, in particular those of the sex determining region (SRY). In cattle, the most frequent cases of intersex are found in females which are co-twins with males (freemartin syndrome) because of placental anastomoses between the two co-twins. While male co-twins are generally normal, female co-twins are sterile but with normal external features. A few cases of XY intersexes have been reported as gonadal digenesis, true hermaphrodites and pseudohermaphrodites . Sex reversal seems to be much more common in horses, and several cases have been reported. In river buffalo, only two cases of sex chromosome abnormalities have been reported: a female which was trisomic, and a female which was monosomic for X chromosomes. The female which was trisomic was 10 years old and had two births, whereas the monosomic female was four-years-old and sterile. This short communication describes the first case of a female river buffalo 2n=50,XY with gonadal dysgenesis, otherwise known as Swyer's syndrome. A normally developed five-year-old female river buffalo with reproductive problems, had prominent withers, as in males, a horn base with a circumference of 38 0 cm (26 to 28 cm in normal females), a pubic bone shorter than normal, a normal vagina, a normal vestibule, and a normal clitoris. The buffalo was slaughtered due to its infertility. Subsequent anatomical observation of the reproductive organs revealed slight hypoplasia of derivative Muller's ducts, small cervix uteri, very small gonads with ovary structure, a slight hydrosalpingitis, and a well-developed uteri interhorn ligament. Peripheral blood cultures were performed using two experiments. Cells were left untreated or treated with 5-bromo-2'-deoxyuridine (B3rdU) and bisbenzimize dye (33258; Hoechst) (15 pg/ml each) six hours before harvesting to obtain normal chromosome preparations and chromosomes with R-banded patterns, respectively. Slides obtained from norm3al cultures were treated for CBA-banding as described by Sumner (1972), and acridine orange staining. Slides treated with BrdU were stained with Giemsa to obtain R13(;-banding. River buLtffalo chromosome identification followed the standard karyotype. Two hundred cells were examined from the tvo cultures, and all showed a male constitution (2n=50,XY), as demonstrated by both CBA-banding and RBG-banding techniques. Despite external female sex structures (normal vagina, vestibule and clitoris), both the horns (larger than in normal females) and withers (prominent as in males) suggested the action of Y-specific genes affecting the body conformation. However, the absence of testicles caused the lack of Mullerian regression factor production and this justifies the development of Mullerian duct derivatives, even when the Y chromosome was present. This study demonstrates that both breeders and veterinary practitioners should be alert during animal breeding to avoid such problems as retaining females which never produce calves (or milk) on a farm. The female river buffalo in this study showed some clear male features (horns and withers) which should have suggested earlier cytogenetic investigation.