A Novel Frequent BRCA1 Allele in Chinese Patients with Breast Cancer

The whole length of exon 11 of BRCA1 was sequenced （total 3427 bp） in 59 patients and 10 healthy female blood donors. To allow a rapid determination of the different BRCA1 alleles, a sequence-specific primer PCR method （PCR-SSP） was established and was applied to 57 additional female donors. Finally, the full-length coding region of BRCA1 was analyzed through reversed-transcriptase PCR （RT-PCR） and cDNA sequencing （total 5554 bp） in one donor with wild-type allele and 2 patients with one or two mutated alleles. By genomic DNA sequencing, 5 homozygous polymorphisms were observed in 18 patients： 2201C〉T, 2430T〉C, 2731C〉T, 3232A〉G and 3667A〉G All of them were previously observed in Caucasians, Malay and Chinese, but for the first time the mutations were found in one allele （GenBank AY304547）. Twenty-six patients and 4 donors were heterozygous at these 5 nucleotide positions. The remaining 15 patients and 6 donors showed a sequence identical with the standard BRCA1 gene. Combined the PCR-SSP results and in a summary, 6 of 67 （9.0 %） healthy individuals were homozygous for the mutated allele, whereas 18 of 59 （30.5 %） breast cancer patients were homozygous. A Chi-square test showed a significant correlation between homozygous mutated BRCA1 allele and breast cancer. The cDNA sequencing showed that 2 additional mutations, 4427T〉C in exon 13 and 4956A〉G in exon 16, were found. A new BRCA1 allele, which is BRCA1-2201T/2430C/2731T/3232G/3667G/4427C/4956G （GenBank AY751490）, was found in Chinese. And the homozygote of this mutated allele may implicate a disease-association in Chinese.