我们在临床上观察到遗传性非息肉病性结直肠癌（HNPCC）患者的结直肠癌发生情况存在较大个体差异，即便在携带相同致病基因突变的患者中，发病年龄也存在很大差别，甚至有的突变携带者不发生结直肠癌。这种表型差异除了与遗传因素有关外，和肠道微生物群也可能有关系。本研究将通过宏基因组测序技术，比较HNPCC家系中，携带相同种系基因突变、但结直肠癌发病表型不同患者的肠道微生物群多样性差异，以及HNPCC患者与同一家系中正常人的肠道微生物群多样性差异，以找到可能影响HNPCC发病的肠道微生物种属。并明确这些微生物对HNPCC发生的保护或致病作用的具体机制。本研究对明确肠道微生物在结直肠癌发生中的作用有重大意义。

We found the tumorigenesis of hereditary nonpolyposis colorectal cancer (HNPCC) was different between various patients. Even among patients with same mutations, the age of onset was varied. And some mutation carriers were clear of colorectal cancer. This variance of phenotype should have matter with intestinal microbiota as well as genetic factors. Therefore, in this study we will compare the intestinal microbiota in HNPCC patients with various colorectal phenotypes through metagenomic sequencing. We hope to find some gut microbes which contribute to tumorigenesis of HNPCC, and the underlying mechanism of microbes preventing or promoting HNPCC. This study is important in discovering the role of microbes in colorectal carcinogenesis, and the potential chemoprevetion methods of CRC.