Cloning and characterization of an unstable CGG repeat related to a fragile site in Xq28: A FRAXF candidate
- Baylor College of Medicine, Houston, TX (United States); and others
Three folate-sensitive fragile sites have been identified in distal Xq, and have been termed FRAXA, FRAXE and FRAXF. The former two have been characterized at the molecular level and found to contain expanded stretches of CGG repeats within hypermethylated CpG islands. We have isolated a cosmid clone that likely represents FRAXF. Somatic cell hybrid analysis maps the cosmid to Xq28 between IDS and GABRA3, the region to which FRAXF has been localized. A 5kb EcoRI fragment of the cosmid detects a fragment increased by 900 base pairs in a mentally retarded male exhibiting 28% fragile site expression. By DNA analysis this patient demonstrates normal alleles at both FRAXA and FRAXE. The proband`s DNA at this locus is methylated at three sites (SacII, EagI, and BssHII) within the CpG island. Additional normal and retarded family members were tested both for fragile site expression and for expansion and methylation at this locus; the expansion and methylation are found only in individuals expressing the fragile site, suggesting that this clone does represent the fragile site. Inheritance of the fragile site does not show a direct correlation with the mental impairment in this pedigree. The site of variation was localized to within 300 base pairs. By sequence analysis, the plasmid subclone contains (CGG){sub 8}. PCR primers were designed to amplify across the repeat. Expanded alleles amplify poorly or not at all, which is consistent with difficulties observed with FRAXA. Alleles in the normal population vary from 6 to 29 repeats. Fluorescence in situ hybridization studies are currently under way to demonstrate unequivocally that this clone spans the fragile site in the patient mentioned above. Efforts to define the gene content of the region are under way, in order to determine the potential involvement of this repeat in regulation of genes in its vicinity.
- OSTI ID:
- 133305
- Report Number(s):
- CONF-941009--
- Journal Information:
- American Journal of Human Genetics, Journal Name: American Journal of Human Genetics Journal Issue: Suppl.3 Vol. 55; ISSN AJHGAG; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
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