Y-Chromosome Detection in Turner Syndrome

Abstract

Introduction: Turner syndrome (TS) is a chromosomal disorder characterized by the presence of a single normal X chromosome in women. The incidence of this disease is approximately 1 in 2500 live female births being the unique monosomy compatible with life. A 45,X karyotype is observed in ~1-2% of conceptuses, 10% of miscarriages and 1% of stillbirths. More than 99% of 45,X conceptuses result in spontaneous loss, usually before 28 weeks. In TS, 95- 98% of women are infertile. This is due to accelerated loss of oocytes from the ovaries after the 18th week of fetal life or over the first few postnatal months or years. Spontaneous pregnancies have been reported, especially in women with TS mosaicism, but also in women with non-mosaic TS. Additionally to the X chromosome monosomy, other cell lines could co-exist, containing two or more X chromosomes, even containing structural abnormalities and also cell lines containing the Y chromosome or part of it. The presence of Y chromosome in patients with TS represents an increased risk (15-30%) of developing gonadoblastoma, a neoplasia composed of germ cells and sex cord elements with a good prognosis if detected early in life. It has been suggested that a locus (GBY) predisposing to the development of this tumor is located in the pericentromeric region of Yp. The aim of this study was to determine the presence of different genes mapped on Y chromosome in Turner syndrome patients and develop a molecular test for detection of Y chromosome sequences, not detected by conventional cytogenetic techniques. Material and Methods: DNA Samples from 107 TS patients, including 83 samples of peripheral blood, 5 of amniotic fluid and 19 miscarriages samples. Peripheral blood lymphocytes and fibroblasts were cultured using conventional methods to perform a karyotype. DNA was extracted from cells fixated in methanol:acid acetic and analyzed by polymerase chain reaction (PCR) technique. This technique was used to analyze the presence of genes mapped on Y chromosome, two mapped on the short arm (SRY and TSPY) and two on the long arm (DDX3Y and HSFY1). Results: From a total of 83 samples of peripheral blood, 8 patients exhibited karyotype 45,X, 75 exhibited mosaic cell lines and 9 has structural abnormalities of the X chromosome. From the 19 samples of miscarriages samples, 17 patients has karyotype 45,X, 1 exhibited a mosaic cell line and 1 exhibited mosaic cell line and abnormalities of the X chromosome. All 5 samples of amniotic fluid presented karyotype 45,X. The PCR technique revealed the existence of hidden mosaics not detected by cytogenetic analysis. From 107 cases analyzed, 9 cases could not be amplified due to bad DNA quality. In the remaining 98 samples, SRY sequence was detected in 3,06% (3/98), TSPY in 2,04% (2/98), DDX3Y in 1,02% (1/98). A frequency of 4,8% (4/98) of samples with Y chromosome material present in minority cell line was detected using the PCR technique. Conclusions: Detection of Y chromosome mosaicism is clinically important, due to the increased risk of tumor formation, especially gonadoblastoma in TS patients with normal, structurally abnormal, or hidden Y chromosome. The prophylactic gonadectomy is the procedure of choice to exclude gonadal malignancy in TS patients carrying Y chromosome sequences. This type of analysis should be a complementary diagnostic method contributing to a more accurate clinical diagnosis. Oocyte donation is an option in the treatment of fertility in TS. Pregnancy rates of TS subjects have been similar to those among other women in oocyte donation programmes. One treatment option in the future might be cryopreservation of ovarian tissue at a young age and later re-implantation or maturation of ovarian follicles in vitro.