Abstract
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.
Original language | English (US) |
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Pages (from-to) | 52-57 |
Number of pages | 6 |
Journal | American journal of medical genetics |
Volume | 93 |
Issue number | 1 |
DOIs | |
State | Published - Jul 3 2000 |
Keywords
- Inactive r(X)
- Mental retardation
- Parental origin of ring X chromosomes
- Ring X chromosome
- Severe phenotype
- Turner syndrome
- XIST
ASJC Scopus subject areas
- Genetics(clinical)