Genetic diagnosis strategy of hereditary non-polyposis colorectal cancer

Abstract

Aim: To study the characteristics of mismatch repair gene mutation of Chinese hereditary non-polyposis colorectal cancer (HNPCC) and hMLH1 gene promoter methylation, and to improve the screening strategy and explore the pertinent test methods.

Methods: A systematic analysis of 30 probands from HNPCC families in the north of China was performed by immunohistochemistry, microsatellite instability (MSI), gene mutation and methylation detection.

Results: High frequency microsatellite instability occurred in 25 probands (83.3%) of HNPCC family. Loss of hMLH1 and hMSH2 protein expression accounted for 88% of all microsatellite instability. Pathogenic mutation occurred in 14 samples and 3 novel mutational sites were discovered. Deletion of exons 1-6, 1-7 and 8 of hMSH2 was detected in 3 samples and no large fragment deletion was found in hMLH1. Of the 30 probands, hMLH1 gene promoter methylation occurred in 3 probands. The rate of gene micromutation detection combined with large fragment deletion detection was 46.7%-56.7%. The rate of the two methods in combination with methylation detection was 63.3%.

Conclusion: Scientific and rational detection strategy can improve the detection rate of HNPCC. Based on traditional molecular genetics and combined with epigenetics, multiple detection methods can accurately diagnose HNPCC.

Figure 1

Large fragment deletion results with MLPA technique. A indicates peak graph of fluorescence intensity of proband PCR products. B indicates peak graph of fluorescence intensity of control PCR products. ↓ indicates large fragment deletion in exon.

Figure 2

Electropherogram of hMLH1 gene promoter methylation detection. M: Methylation; U: Non-methylation; H: Family number. H8 manifests partial methylation. H6 and H28 manifest exhaustive methylation.