A Rare Case of Mosaic Ring Turner Syndrome with Horseshoe Kidney

Rearranged X chromosomes in Turner syndrome (TS) generally present with a mild phenotype, but in cases of ring X chromosomes, the incidence of intellectual disability and other congenital abnormalities can be significantly higher depending on the size of the ring and the involvement of X-inactive specific transcript (XIST) region. Here, we report a 17-year-old female who was referred for a cytogenetic analysis because of primary amenorrhoea. The patient, of normal intelligence, had been found to have traits of TS, especially short stature and some rare findings such as horseshoe kidney and short fourth toe. Cytogenetic analysis showed a mosaic 45, X/46, X and r(X) karyotype. Fluorescence in situ hybridisation analysis using sex chromosome probes permitted us to identify the marker as a ring X chromosome, detected in 30% of cells. The r(X) might include the XIST locus, which would have caused X-inactivation of this abnormal ring chromosome leading to mild phenotype in our patient but with atypical features present in the form of horseshoe kidney and short fourth toe.