Molecular characterization of tiny ring X chromosomes from females with functional X chromosome disomy and lack of cis X inactivation
- Johns Hopkins Univ., Baltimore, MD (United States); and others
Small ring X chromosomes were first described in mosaic karyotypes of females with the relatively benign phenotype of Turner syndrome. The presence of these rings in association with more severe phenotypes including mental retardation has raised the possibility that they lack sequences necessary for X chromosome inactivation center (XIC) essential for cis X-inactivation. The authors recently showed that ring X chromosomes ascertained because of the severe phenotype do not express XIST, a candidate for the relevant gene, and that they are in fact active chromosomes. They now report studies of the genetic content of 11 of these ring X chromosomes (9 associated with severe phenotypes). The results indicate that these chromosomes contain contiguous segments of DNA and have variable proximal and distal breakpoints and some include mainly long arm or mainly short arm sequences. As expected for ring chromosomes, they lack telomeric sequences. Many of the ring chromosomes lack the XIST locus, consistent with XIST being necessary for cis inactivation. However, the breakpoints in four ring chromosomes that have XIST sequences but do not express XIST suggest that other sequences within the XIC distal to XIST as it is now defined are also needed. 39 refs., 2 figs., 2 tabs.
- OSTI ID:
- 114901
- Journal Information:
- Genomics, Journal Name: Genomics Journal Issue: 1 Vol. 27; ISSN GNMCEP; ISSN 0888-7543
- Country of Publication:
- United States
- Language:
- English
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