The Detection Of Large Gene Rearrangements In HNPCC And The Data Analysis Of Related MMR Genes

Hereditary Non-polyposis Colorectal Cancer (HNPCC) is an autosomal dominant inheritance syndrome. It is the most common hereditary variant of colorectal cancer (CRC), which accounts for 2-5% CRCs. Compared with the sporadic colorectal cancer (SCRC) and the familiar adenomatous polyposis (FAP), HNPCC has significant differences in the mechanism of disease, clinical features, and the therapeutically plans. So it is important to classify HNPCC from colorectal cancer. There have been several clinical criteria of identifying HNPCC, but the only way to confirm HNPCC is to detect the defects of MMR (Mismatch Repair) genes. The MMR genes related to HNPCC include MLH1, MSH, MSH6, PMS2, PMS1 and MLH3 gene. About 90% of the mutations take place in MLH1 and MSH2 genes. However, most studies are focused on the small mutations of MMR genes. In this circumstance, large gene deletion or duplication is missing in the results of most researches. Indeed, the large gene deletion or duplication takes up about 17% in all the defects that causes HNPCC in MLH1 and NSH2 genes.And some reported data shows the percentages of large gene deletion in different countries are different from each other.Meanwhile, as the importance of MMR genes in HNPCC and the increasing reported mutation data, many databases have been built to provide a stage for researchers to get share information. Among all the databases, the InSiGHT database is the most influential one. The International Society of Gastrointestinal Hereditary Tumors (InSiGHT) set up a database about the mutations which are associated with HNPCC (http://www.insight-group.org/mutations/). The database has collected a large number of mutation data,and iswidely used by the researchers all over the world. Till March 2014, the database has collected information of 10 genes that are related to colorectal and gastric cancer. There are in total 12628 data items of the 6 HNPCC related genes, take up 48% of the total number. The number of data items for MLH1, MLH3, MSH2, MSH6, PMS1 and PMS2 are 6491,148,5016,1506,1 and 520 respectively.Our study would make further research on HNPCC from two aspects. On one hand, as the studies of large gene deletion are relatively few in China, we obtained our 60 patients and 3 control samples from Shanghai Cancer Hospital and extracted the DNA. We used the MLPA (Multiplex ligation-dependent probe amplification) method to detect large gene deletion, and the results show:10 patients in 60 have got large gene deletion,3 (5%) in gene MLH1 and 7 (11.7%) in MSH2. The 16th exon in MLH1 and the 9th and third exons in MSH2 have higher frequency of large gene deletion. By comparing with previous data and clinical data, the patients are generally younger, and the family information and clinical criteria are not enough to diagnose HNPCC. The molecular detection is needed. Yet there is no overlap between patients with large gene deletion and spot mutation, which means in molecular detection we need to add the detection of large gene deletion.On the other hand, the InSiGHT database has cumulated large number of mutations, but few studies have focused on the statistical analysis of the reported data. Our lab has made statistical analysis on gene MLH1 and MSH2,but still remains some MMR genes, such as MSH6, PMS2 and MLH3, which are also important especially from statistical aspect. In this study, we collected all the related literatures and extracted the useful information to build a database and make further analysis. Our results show:each gene of MSH6, PMS2 and MLH3 has its own hot spots and exons, which we might pay special attention to when processing the clinical detection and diagnosis. And although Asian population takes up the minority of the total patients, there are still some important hot spots and exons, such as exon 5 in MSH6 and the mutation spots c.691A>C, c.2896T>C and C.2825C>T in MLH3, that are different from the total sample and need to pay special attention to. For the patients with mutations of MSH6, many of them get more than one attack and have a relatively later age (around 50). And it is worth mentioning that most women (51.3%) got both colorectal cancer and endometrial cancer, which implies that when diagnosing colorectal cancer, it is necessary for women to detect the female reproductive systems such as the uterus and ovary.