Novel aphidicolin-inducible common fragile site FRA9G maps to 9p22.2, within the C9orf39 gene.

Common fragile sites represent a component of normal chromosome structure that form gaps and breaks on metaphase chromosomes after partial inhibition of DNA synthesis. In humans, cytogenetic locations of 89 common fragile sites are listed in the Genome Database; however, the exact number of fragile sites remains unknown. The application of high resolution mapping approaches continues to reveal new common fragile sites in the human genome. Here, we identified a novel aphidicolin-inducible common fragile site FRA9G, which maps to chromosomal band 9p22.2. We have characterized the structure of the fragile DNA sequence that extends over a genomic region of approximately 300 kb within the C9orf39 (chromosome 9 open reading frame 39) gene. Analysis of incidence in healthy individuals showed that FRA9G is commonly expressed in the population. Heterozygous BRCA2 mutation carriers exhibit an almost sevenfold increase of FRA9G expression compared to an unrelated control population group. Identification of a novel aphidicolin-inducible common fragile site at 9p22 may have implications for understanding the mechanism of genetic instability in tumorigenesis and other genetic disorders.