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PubMed · 10222796

[FRAXE mental retardation].

T Yamagata
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Abstract

The folate sensitive fragile site FRAXE is located in Xq28, 600 kb distal to the fragile X syndrome (FRAXA) fragile site. An unstable GCC triplet repeat responsible for FRAXE exists in the 5' untranslated region of FMR2 gene. Normal alleles range from 10-35 repeats and more frequently 15-20 GCCs. An expanded GCC repeat over 200 is methylated, inactivates FMR2, and results in FRAXE mental retardation. Affected individuals show mild mental retardation and/or autistic symptoms FMR2 is a large gene consisting of 21 exons spanning about 600 kb. FMR2 mRNA is about 9.5 kb and is expressed in the brain(especially in the hippocampus and the amygdala) in adults and also in placenta. The FMR2 protein is 1311 amino acids, contains nuclear localization signals, and is a putative transcription factor.

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Chromosome Fragile SitesChromosome FragilityFragile X SyndromeHumansNuclear ProteinsProteinsTrans-ActivatorsTrinucleotide RepeatsEnglish AbstractJournal ArticleReview

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T Yamagata. 1999. [FRAXE mental retardation].. https://pubmed.ncbi.nlm.nih.gov/10222796/

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Common fragile sites as targets for chromosome rearrangements.

Common fragile sites are large chromosomal regions that preferentially exhibit gaps or breaks after DNA synthesis is partially perturbed. Fragile site instability in cultured cells is well documented and includes gaps and breaks on metaphase chromosomes, translocation and deletions breakpoints, and sister chromosome exchanges. In recent years, much has been learned about the genomic structure at fragile sites and the cellular mechanisms that monitor their stability. The study of fragile sites has merged with that of cell cycle checkpoints and DNA repair, with multiple proteins from these pathways implicated in fragile site stability, including ATR, BRCA1, CHK1, and RAD51. Since their discovery, fragile sites have been implicated in constitutional and cancer chromosome rearrangements in vivo and recent studies suggest that common fragile sites may serve as markers of chromosome damage caused by replication stress during early tumorigenesis. Here we review the relationship of fragile sites to chromosome rearrangements, particularly in tumor cells, and discuss the mechanisms that may be involved.

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