Small marker X chromosomes lack the X inactivation center: Implications for karyotype/phenotype correlations
- Western Reserve Univ., Cleveland, OH (United States)
- Queen's Univ. and Kingston General Hospital, Ontario (Canada)
- Univ. of Pittsburgh, PA (United States)
The abnormal phenotype and/or mental retardation seen in persons with small marker X (mar(X)) chromsomes has been hypothesized to be due to the loss of the X inactivation center (XIC) at Xq31.2, resulting in two active copies of genes in the pericentromeric region. In order to define precisely the DNA content of mar(X) chromosomes and to correlate phenotype with karyotype, the authors studied small mar(X) chromosomes, using FISH with probes in the juxtacentromeric region. One of the probes was a 40-kb genomic cosmid for the XIST gene, which maps to the smallest interval known to contain the XIC and is though to be involved in X inactivation. The findings reveal that small mar(X) chromosomes do not include the XIC and therefore cannot be subject to X inactivation, supporting the premise that abnormal dosage of expressed genes in the pericentromeric region of the X generates the aberrant phenotype seen in patients with small mar(X) chromosomes. 54 refs., 4 figs., 2 tabs.
- OSTI ID:
- 7061994
- Journal Information:
- American Journal of Human Genetics; (United States), Vol. 55:1; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
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