Severe phenotypes associated with inactive ring X chromosomes
Mental retardation and congenital malformations in individuals with small ring X chromosomes are often due to the functional disomy that results from failure of these chromosomes to undergo X inactivation. Such chromosomes either lack the XIST locus or do not express it. We have carried out genetic...
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Veröffentlicht in: | American journal of medical genetics 2000-07, Vol.93 (1), p.52-57 |
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Sprache: | eng |
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Zusammenfassung: | Mental retardation and congenital malformations in individuals with small ring X chromosomes are often due to the functional disomy that results from failure of these chromosomes to undergo X inactivation. Such chromosomes either lack the XIST locus or do not express it. We have carried out genetic analysis of the ring X chromosomes from two girls with a 45,X/46,X,r(X) karyotype, mental retardation, and a constellation of abnormalities characteristic of the severe phenotype due to X disomy. In each case the ring X chromosome included an intact XIST locus which was expressed; the breakpoints were distal to DXS128, and therefore outside the XIC region; transcription analysis of alleles at the androgen receptor locus confirmed that these were inactive chromosomes. The characteristics of the XIST RNA were similar to the wild‐type. Additional studies in cultured fibroblasts showed a second ring in a small percentage of the cells. The association of severe phenotype with an inactive X chromosome most likely reflects the presence of a second ring X chromosome which was active at least in some tissues during embryogenesis, but is no longer prominent in the tissues we analyzed. Am. J. Med. Genet. 93:52–57, 2000. |
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ISSN: | 0148-7299 1096-8628 |
DOI: | 10.1002/1096-8628(20000703)93:1<52::AID-AJMG9>3.0.CO;2-9 |