The Study Of BRCA1, BRCA2 And DBC2 Gene Mutation In The Early Onset And Non-familial Breast Cancer Patients From East China

【Backgroud】Breast cancer is a common malignancy among women which threat to their health seriously.The study of susceptibility gene of breast cancer has been one of the hot and BRCA1 and BRCA2 are most important genes among them. As a tumor suppressor gene which is related to sporadic breast cancer,DBC2 was found lost in about 60% breast cancer patients.As a tumor suppressor gene which was found in familial breast cancer earliest, BRCA1 is located in human chromosome No.17 from the 22 coding exons and two non-coding exon (exon 1 and 4) constitute a total distance of about 100kb, encoding a 1863 amino acid protein composed of multifunctional area. And the whole genome DNA of BRCA2 is about 70kb, which contains the coding region 10987bp. BRCA2 gene mapping in the 13q12-13, contains 27 exons, encoding 3418 amino acids. DBC2 is also a tumor suppressor gene which located at human chromosome 8p21 and its total length is about 20.5Kbp. DBC2 is also named Rhobtb2.Studies have proved that breast cancer is a genetic predisposition disease in which 5-10% from family genetic, and 90-95% for sporadic breast cancer. The mutation of it's susceptibility gene BRCA1 and BRCA2 have a highly relevant with the tumorigenesis of breast cancer. Once a patients have this mutant gene, all offspring of her family members have the 50% chance for carrying it. If a 40-year-old womon carries a mutant BRCA1, she may have the 20% chance of occurrece of breast cancer. DBC2 is an atypical Rho GTPase its common function is to prevent the proliferation of abnormal cells which is related to the developing of tumor. The growth of breast cell line can be inhibited when DBC2 gene is inducted into it, while the growth of tumor cell can't be restricted when DBC2 gene has natural mutation in the breast cancer,suggesting that DBC2 gene may play an important role as an gene impressor in breast cancer.Currently, early-onset breast cancer has become more and more common, especially in China. The age of incidence of breast cancer is 10-15 years earlier than that in Western country. In our research, we study the gene polymorphism of BRCA1/2, DBC2 in East China early-onset non-familial breast cancer patients and healthy population.【objective】In our research,we study the gene polymorphism of BRCA1, BRCA2, DBC2 in East China early-onset non-familial breast cancer patients and healthy population.【method】The object comes from 45 example precocity non-familial breast cancer in East China, who were diagnosed before the age of 40 years were analyzed, carries on the circumference blood genome team DNA extraction with 30 example normal people. After PCR amplification was carried out in the 5th exon of DBC2, the 11th,24th exon of BRCA1,the 11th exon of BRCA2. The PCR production was be sequenced. All have been done to analyze the relationship between the gene mutation and breast cancer.【result】(1) There is a novel missense mutation A>G we have detected,located in the 11th exon of BRCA1 in one cases out of 45 early onset and sporadic breast cancer cases. There is 12 cases carried heterozygosis and 1 case carried homozygote mutation. The genotype distributions of the control group and breast cancer group were in the Hardy-Weinberg equilibrium, with a representative group. Three cases of Group AA genotype frequencies were 32 cases of type, GA 12 cases, GG 1 cases; but in the control group of three AA genotype frequencies were 30 cases of type. The difference was not significan(tP>0.05)between the two groups; G allele was significantly higher than in the case. It was not the difference significant with statistically(P>0.05).(2) There is a novel missense mutation +7776C>T(P.Leu288Phe) we have detected,located in the 5th exon of DBC2 in 8 cases out of 45 early onset and sporadic breast cancer cases. The mutation rate is 17.78%,but there is no mutation in the control group. After Fisher's exact test, we conclude that the mutation rate of 5th exon in cases is higher than control groups(one-sided p value is 0.0186,two-sided p value is 0.0371). (3) We have not found any SNP site of the 24th exon of BRCA1,the 11th exon of BRCA2 in both groups, there is no variability of mutation rate between two groups.【conclusion】(1) The novel mutation rate of 3142A>G in 11th exon of BRCA1 gene is lower in breast caner cases than the control groups. It is the homozygous mutation. Others are heterozygous mutations in 12 cases. It may be the special mutation site in the early onset and sporadic breast cancer patients of China. And may contribute to the predisposition for the early onset and sporadic breast cancer and be a mutation site of high risk gene of breast cancer in the early onset and sporadic breast cancer in China.Thus,we could build a platform to screen the susceptible population of breast cancer patients,which would benefit to some aspects of society and economy. A further study would be needed to confirm the results.The study on the function of the mutation site and the screen to the first degree relative of patient who has the positive mutation will be continued.(2) The novel mutation rate of +7776C>T in 5th exon of DBC2 gene is higher in breast caner cases than the control groups.(3) By comparing the characterictics of patients with the mutation in the 5th exon of DBC2 with that who have not, we found that there are no variability in age of onse(tP>0.05), rate of positive ER(two-sided p value is 0.2693) ,PR(two-sided p value is 1.0868),Her-2(two-sided p value is 1.0888).