Clinicopathological and molecular genetic analysis of 4 typical Chinese HNPCC families

Abstract

Aim: To study the clinicopathological and molecular genetic characteristics of typical Chinese hereditary nonpolyposis cotorectal cancer (HNPCC) families.

Methods: Four typical Chinese HNPCC families were analyzed using microdissection, microsatellite instability analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes.

Results: All five tumor tissues of 4 probands from the 4 typical Chinese HNPCC families showed microsatellite instability at more than two loci (MSI-H or RER+ phenotype). Three out of the 4 cases lost hMSH2 protein expression and the other case showed no hMLH1 protein expression. Three pathological germline mutations (2 in hMSH2 and 1 in hMLH1), which had not been reported previously, were identified. The same mutations were also found in other affected members of two HNPCC families,respectively.

Conclusion: Typical Chinese HNPCC families showed relatively frequent germline mutation of mismatch repair genes. High-level microsatellite instability and loss of expression of mismatch repair genes correlated closely with germline mutation of mismatch repair genes. Microsatellite instability analysis and immunostaining of mismatch repair gene might serve as effective screening methods before direct DNA sequencing. It is necessary to establish clinical criteria and molecular diagnostic strategies more suitable for Chinese HNPCC families.

Figure 1

Four typical Chinese HNPCC pedigrees.

Figure 2

MSI status of H2 proband. Microsatellite analysis of H2 proband with five microsatellite markers, MSI in 4/5 loci.

Figure 3

Immunohistochemical staining. No hMSH2 protein expression in adenoma and carcinoma areas of H11 proband tumor section, infiltrating lymphocytes as well as normal colonic crypt epithelium next to the tumor showed nuclear staining of the hMSH2 protein. × 100

Figure 4

Immunohistochemical staining. A: No hMLH1 protein expression in carcinoma area of H9 proband tumor section. × 400 B: Infiltrating lymphocytes as well as normal colonic crypt epithelium next to the tumor showed nuclear staining of the hMLH1 protein. × 200

Figure 5

C-T transition (CGA-TGA) at codon 680 in ex on 13 of hMSH2 gene in H2 proband, resulting in a stop codon.

Figure 6

A 24 bp deletion at codon 305 in exon 11 of hMLH1 gene in H9 proband.

Figure 7

A 1 bp insertion at codon 206 in exon 3 of hMSH2 gene in H27 proband, resulting in a stop codon 73 bp downstream of the mutation.