Background. According to the literature approximately 50% of patients with Turner’s syndrome have karyotype 45,X in every cell, the rest have two or more cell lines with mosaics of sex chromosomes. New methods have shown that the mosaicism is probably more frequent than expected from classical cytogenetics examinations. The aim of this study was to detect numerical changes of sex chromosomes in mitoses and interphase nuclei of cultivated peripheral lymphocytes of patients with Turner’s syndrome by means of FISH, to compare the sensitivity of classical and molecular-cytogenetic methods and to estimate the values obtained in 10 control healthy females with karyotype 46,XX. Methods and Results. 18 females with Turner’s syndrome were examined. Karyotype 45,X was found by classical cytogenetics in all cells of 9 females. The 9 remaining patients had sex chromosome mosaicism of two or more clones. In all patients FISH confirmed the results of classical cytogenetic methods and in 6 patients (30%) it revealed other clones previously not detected. Conclusions. Higher sensitivity of FISH enables more precise detection of mosaicism of cell lines than classical cytogenetics and this technique is more suitable for examinations of patients with Turner’ syndrome.

        Key words: Turner’s syndrome, FISH, X chromosome, interphase cell.