Cytogenetic analyses revealed various karyotype presentations in our patients. A classical 45,X non mosaic karyotype was identified in 50% of the patients, which corresponds to findings of other authors (40-60%) [4-6]. However, the number of tissues and cells examined influenced detection of mosaicism. For example, when both peripheral lymphocyte and fibroblast cultures were evaluated, only 20.7% of karyotypes of 87 live born Turner syndrome patients were found to be 45,X [8]. We found unidentifiable marker chromosomes in 7.5% of the patients, which is much higher than previously reported (3%) [5]. Our molecular analyses did not identify any of the markers as originating from the Y chromosome, whereas others have found up to 50% of markers to have Y chromosomal origin [7]. The difference of Y-chromosome-positive patients in different studies is caused by the different sensitivity of the methods applied.

      Apparent association has been found between Y chromosome material (in sex-reversed females caused by deletion/mutation of the SRY gene or in Turner syndrome patients with Y chromosomal mosaicism) and an increased risk of appearance of gonadoblastoma in the dysgenetic gonad [11], which led to the hypothesis of a Y chromosomal locus (referred to as gonadoblastoma locus on the Y chromosome or GBY) that increases susceptibility to gonadoblastoma development [28]. Based on deletion mapping in phenotypic females with gonadoblastoma and partial Y chromosome, GBY was localized to a region near the centromere on either arm of the Y chromosome [28]. Detailed deletion mapping of the human Y chromosome in 10 patients with gonadoblastoma, six having a rearranged Y chromosome, further localized the gonadoblastoma critical region to a 1-2 Mb of Yp near the centromere [12].

      Pubertal virilization in some Turner syndrome patients represents an alarming sign of an undetected Y-chromo-some-positive cell line that increases the risk for development of gonadoblastoma. This raised the question of the diagnostic and therapeutic difficulties due to the small number of XY cells [21]. In this sense, detection of the SRY gene represents a valuable and sensitive method in detection of an unrecognized Y-chromosome-positive cell line and may alter the therapeutic approach.

      We detected the SRY gene in peripheral blood leucocytes of two patients with the mos 45,X/46XY karyotype, whereas all other patients were SRY negative. This low incidence (5%) of SRY-positive results in Turner syndrome patients agrees with the results of other studies [29,7,26]. One of these studies [26], cytogenetically detected two mosaics for a Y-chromosome-positive cell line in 41 patients examined, who were subsequently verified as SRY-gene positive (4.87%). More sensitive techniques have detected a higher percentage of SRY-gene positive patients (12 [5], 13.3 [30]). The sensitivity of SRY-PCR was increased through Southern blotting of the PCR products, a method that can detect one Y-chromosome bearing cell in 100,000 cells and found 33.3% of Turner syndrome patients to be SRY-positive [21].

      Epidemiological studies in Denmark have questioned the postulated high incidence of gonadoblastoma in Turner syndrome patients [31,32]. Nevertheless, because of the increased risk of gonadoblastoma in Turner syndrome patients with Y-chromosome material [11], the possibility of “low-level hidden” mosaicism for a Y-chromosome-positive cell line in the gonads, the variable age of expression [10], the high malignancy potential of gonado­blastoma and the necessity of timely referral for gonadec­tomy, analysis of SRY should be offered to all Turner syndrome patients.        

      We are aware that increased sensitivity of our technique can be obtained by using either a nested PCR, by transfer of the PCR products on a nylon membrane and hybridization with a labeled probe, or by adding additional probes for the Y chromosome. However, we aimed to establish a simple, easily reproducible, cost-effective and yet sufficiently sensitive method for SRY gene detection with a clinical applicability.