微小RNA(miRNA)通过与靶基因3’UTR结合对基因转录进行调控，在结直肠癌的发生中起到重要作用。现有研究表明miRNA介导的碱基切除修复(Base excision repair, BER)基因表达异常与结直肠癌发生密切相关，而BER基因3’UTR的单核苷酸多态性变异与结直肠癌的关联研究较少且缺乏后续功能论证。本课题拟采用候选基因为基础的关联研究策略，利用生物信息学方法筛选出BER通路基因（OGG1，XRCC1，UNG，SMUG1，MBD4，TDG和MUTYH等）3’UTR的潜在功能性SNP，采用病例对照研究设计并进行大样本基因分型，从单位点及单体型分析探讨SNP与结直肠癌易感性的关系，并在此基础上通过荧光素酶报告基因实验和实时定量PCR等技术，探讨此类SNP对结直肠癌发生的作用。所识别的遗传变异对于筛查个体罹患结直肠癌的风险和人群预防有重要意义。

MicroRNA (miRNA) plays a significant role in gene expression through binding to 3'UTR of target genes, and it participates in colorectal cancer occurrence and development. It is suggested that miRNAs mediated abnormal gene expression of base excision repair parthway is associated with colorectal cancer. Since the studies which exploring the association between SNP located in binding site of base excision repair gene and colorectal cancer are usually rare and lack of follow-up function evidences, the real effects of miRNA are expected to be illuminated in colorectal cancer occurrence. In the present study, we intends to use the candidate genes research strategy. Firstly we will select candidate potential functional SNPs located on miRNA binding sites of base excision repair genes (OGG1, XRCC1, UNG, SMUG1, MBD4, TDG and MUTYH etc.) through bioinformatics approach, then we will employ the case-control study design and genetic typing in a huge population to explore the association between the selected SNPs and colorectal cancer susceptibility from unit point to haplotype analysis, finally we will take advantage of molecular biological technique included luciferase reporter gene test and real-time quantitative PCR technology to investigate the real functional roles of these SNPs. The identification of the genetic variation has important significance in screening and preventing the high risk individuals suffering from colorectal cancer.