Common Fragile Site FRA11G and Rare Fragile Site FRA11B at 11q23.3 Encompass Distinct Genomic Regions

Fragile sites are specific genomic loci that are particularly prone to chromosomal breakage. Based on their incidence in the human population, they are divided into rare fragile sites occurring in less than 5% of all individuals and common fragile sites being a constitutional feature of the genome of probably all individuals. In this study, cloning of unstable DNA sequences, which have been previously genetically tagged with a marker gene, was the basis for defining the genomic localization of the common fragile site FRA11G at 11q23.3. Mapping of the fragile site with six-color fluorescence in situ hybridization (FISH) resulted in the precise genomic localization of FRA11G to a 4.5 Mb region. The chromosomal subband 11q23.3 harbors both the common fragile site FRA11G and the rare fragile site FRA11B. Here, we show that FRA11G maps 0.8 Mb proximal to the genomic region previously defined to be affected by expression of FRA11B; thus, the common and the rare fragile sites at 11q23.3 encompass distinct genomic regions. The region of FRA11G is known to be involved in somatic and germline recurrent aberrations, and it is conceivable that genetic damage resulting from this fragile site might contribute to clinical phenotypes.