Molecular cytogenetic characterization of two Turner syndrome patients with mosaic ring X chromosome
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In the present study, we reported two cases of TS with mosaic ring X chromosome showing common clinical characteristics of TS like growth retardation and ovarian dysfunction. The purpose of the present study was to cytogenetically characterize both cases.
Whole blood culture and G-banding were performed for karyotyping the cases following standard protocol. Origin of the ring chromosome and degree of mosaicism were further determined by fluorescence in situ hybridization (FISH). Breakpoints and loss of genetic material in formation of different ring X chromosomes r (X) in cases were determined with the help of cytogenetic microarray.
Cases 1 and 2 with ring chromosome were cytogenetically characterized as 45, X /46Xr (X) (p22.11q21.32)  and 45, X /46, Xr (X) (p22.2q21.33) , respectively. Sizes of these ring X chromosomes were found to be ~75 and ~95 Mb in cases 1 and 2, respectively, using visual estimation as part of cytogenetic observation. In both cases, we observed breakpoints on Xq chromosome were within relatively narrow region between Xq21.33 and Xq22.1 compared to regions in previously reported cases associated with ovarian dysgenesis.
Our observation agrees with the fact that despite of large heterogeneity, severity of the cases with intact X-inactive specific transcript (XIST) is dependent on degree of mosaicism and extent of Xq deletion having crucial genes involved directly or indirectly in various physiological involving ovarian cyclicity.
KeywordsTurner syndrome Ovarian dysfunction Ring X chromosome Fluorescence in situ hybridization (FISH) Cytogenetic microarray
We thank the parents for giving consent to publish the data. We record words of gratitude to our teacher Professor Rajiva Raman for critical analysis and comments. We are thankful to anonymous reviewers for their suggestions in improving the manuscript. We are thankful to Centre for Genetic Disorders, BHU, for chromosomal analysis and innovative programme of UGC for hormonal assay experiment and Interdisciplinary School of Life Sciences, BHU, Varanasi, for cytogenetic microarrays. Banaras Hindu University, Varanasi, and Indian Council of Medical Research, New Delhi, are highly acknowledged for providing fellowship. This work forms part of the contribution of the Disease biology thrust area under DBT, New Delhi, sponsored by Interdisciplinary School of Life Sciences, BHU.
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