Spectrum of sequence variation in the FANCG gene:: An International Fanconi Anemia Registry (IFAR) study

Fanconi anemia (FA) is a genetically heterogeneous autosomal recessive syndrome associated with chromosomal instability, hypersensitivity to DNA cross-linking agents, and predisposition to malignancy. The gene for FA complementation group G (FANCG) was the third FA gene to be cloned, and was found to be identical with human XRCC9, which maps to 9p13. The cDNA is predicted to encode a polypeptide of 622 amino acids, with no sequence similarities to any other known protein or motifs that could point to a molecular function for FANCG/XRCC9. We used single strand conformational polymorphism analysis (SSCP) to screen genomic DNA from a panel of 307 racially and ethnically diverse unrelated FA patients from the International Fanconi Anemia Registry (IFAR) for variants in FANCG. Twenty-seven abnormal SSCP patterns were found; 18 of these variants appear to be pathogenic mutations while nine are likely to be nonpathogenic polymorphisms. Direct sequencing of genomic DNA from seven FA-G probands with one mutant allele not detected in the SSCP study and three additional probands assigned to the FA-G complementation group by retroviral correction with FANCG resulted in the detection of nine additional pathogenic mutations and two common SNPs. Conditions for rapid screening for these mutations by DHPLC for use in a clinical laboratory setting were established. The most common FANCG mutations in the IFAR population were: IVS8-2A>G (seven Portuguese-Brazilian probands), IVS11+1G>C (seven French-Acadian probands), 1794_1803del10 (seven European probands), and IVS3+1G>C (five Korean or Japanese probands). Our data suggest that the Portuguese-Brazilian, French-Acadian, and Korean/Japanese mutations were likely to have been present in a founding member of each of these populations.