Detection of hMSH2 and hMLH1 mutations in Chinese hereditary non-polyposis colorectal cancer kindreds

AIM： To establish and validate the mutation testing for identification and characterization of hereditary non-polyposis colorectal cancer （HNPCC） in suspected Chinese patients. METHODS： Five independent Chinese kindreds with HNPCC fulfilling the classical Amsterdam criteria were collected. Genomic DNA was extracted after informed consent was obtained. The coding region of hMSH2 and hMLH1 genes was detected by polymerase chain reaction （PCR） and denaturing high-performance liquid chromatography （DHPLC）. Mutations identified in the proband by DHPLC were directly sequenced using a 377 DNA sequencer, analyzed with a basic local alignment tool （BLAST）, and tested in the corresponding family members by direct DNA sequencing. RESULTS： Mutations were identified in two Chinese HNPCC kindreds. One was the missense mutation of hMSH2 c.1808A→G resulting in Asp 603 Gly identified in the proband of the fifth HNPCC （HNPCCS） kindred. In the HNP5 kindred, three family members were found to have this mutation and two of them had colorectal cancer. The other mutation of hMLH1 c.1882A→G was identified in the HNP2 kindred＇s proband, which might be the nonsense mutation analyzed by BLAST. CONCLUSION： Pedigree investigation and mutation testing of hMSH2 and hMLH1 are the practical methods to identify high-risk HNPCC patients in China.

YVDD Mutation of Hepatitis B Virus, a Dominant Lamivudine-Resistant Type in Guangzhou, South China

The epidemiological effects of native and mutated YMDD motif in the HBV genome under the selective pressure of lamivudine were investigated. YMDD wild and mutation motif in HBV genome were detected by flow through reverse dot blots （PT-RDB） with KaiPuTM DNA HybriMax Rapid Hybridization Machine based on the principle of ＂Flow-through hybridization＂ and by the traditional Reverse Dot Blot assay. Sera from 1 021 suspected lamivudine-resistant chronic HBV carriers after more than 8 months of lamivudine therapy and the corresponding archived sera were collected and assayed. We found 35.94% were single type infections with 8.03% YMDD, 7.93% YIDD and 19.98% YVDD. It was also found that 64.06% were mixed infections including 1.96% YMDD and YIDD, 51.62% YMDD and YVDD, 1.96% YIDD and YVDD, 8.52% YMDD, YIDD and YVDD. The levels of infections containing YVDD motif reached 82.08%. The pretreatment infectious status were： YMDD single infection was 36.93%; YIDD single infection was 6.07%; YVDD single infection was 17.04%; YMDD and YIDD mixed infection was 0.97%; YMDD and YVDD mixed infection was 33.99%; YIDD and YVDD mixed infection was 0.98%; YMDD, YIDD and YVDD mixed infection was 4.02%. Infections containing YVDD motif were only 56.03%. The 34.32% mutation rate of YMDD motif to YVDD was significantly higher than the 10.97% of YMDD to YIDD （U=10.98, P〈0.05）, as estimated by Mann-Whitney U-test for non-parametric data. HBV containing YVDD motif might have an evolutionary ascendancy and become the dominant type under the selective pressure of lamivudine.