A novel heterozygous germline deletion in MSH2 gene in a five generation Chinese family with Lynch syndrome

Correlation of MSH2 exonic deletions and protein downregulation with breast cancer biomarkers and outcome in Pakistani women/patients

Mismatch repair (MMR) pathway is one of the underlying mechanisms of predisposition to breast cancer (BC). The present study explored the association of MSH2 exonic deletions, respective survival analysis, protein structure prediction, transcription profiling, and expression analysis with BC risk. Genotyping analysis of 493 BC cases and 387 controls confirmed the association of two MSH2 exonic deletions, i.e., exon 3 (OR:6.4, CI = 3.4-12.1) and 9 (OR:7.8, CI = 4.1-14.8) with BC risk. In order to confirm the phenotypic-genotypic relationship, we have performed MSH2 transcriptomic (p < 0.05) and protein expression analysis (OR:30, CI = 4-230) which further confirmed its downregulation/loss in BC biopsy samples highlighting potential role in the onset of breast carcinogenesis. Additionally, we have presented that MSH2 mutations can alter the expression profile of other BC associated biomarkers like ER, PR, CK-7, GATA-3, and E-cadherin. Subsequently, the effect of exonic deletions on secondary structure of protein has shown missing of beta and alpha helices in their protein products via in-silico analysis. However, loss of exon 3 results in the altered core protein structure leading to dysfunction protein, possible cause of BC development. No association of MSH2 exonic deletions with survival statistics was observed conceivably due to the shorter follow-up time. Thus, our results at genetic, transcriptomic, and proteomic levels confirmed the downregulated MSH2, emphasizing its potential contribution in MMR mechanisms for breast tumorigenesis. In conclusion, MSH2 deficiency may cause breast cancer development and progression.

A Novel Splice-Site Mutation in MSH2 Is Associated With the Development of Lynch Syndrome

Lynch syndrome (LS) is an inherited autosomal dominant disorder caused by germline mutations of mismatch repair (MMR) genes, including MSH2, MSH6, PMS2, and MLH1. This study aimed to analyze the molecular defects and clinical manifestations of an affected family and propose appropriate individual prevention strategies for all mutation carriers. A novel splicing mutation (c.1661+2 T>G) was identified in the MSH2 gene, which was found to co-segregate among affected family members by Whole exome sequencing (WES). RT-PCR analysis confirmed that c.1661+2 T>G could produce 3 transcripts, including 1 normal transcript and 2 aberrant transcripts. The 2 aberrant transcripts resulted in premature termination at the 6th nucleotide codon of MSH2 exon 11, so that the predicted products of the mutant MSH2 mRNAs were truncated proteins of 505 amino acids (with all of exon 10 deleted) and 528 amino acids (with a deletion of 82-nucleotides in exon 10), resulting in the loss of the interaction domain, the ATP domain and post-translationally modified residues. Quantitative RT-PCR (qRT-PCR) analysis showed that MSH2 mRNA levels in all patients were reduced to only 1/4 of the control levels. Our study reveals that a novel splicing mutation (c.1661+2 T>G) in the MSH2 gene causes LS and reaffirms the importance of genetic testing for LS.

A Hereditable Mutation of MSH2 Gene Associated with Lynch Syndrome in a Five Generation Chinese Family

Purpose

In order to clarify which variants of the MMR gene could provide current "healthy" members in affected families a more accurate risk assessment or predictive testing.

Patients and Methods

One family, which meets the criteria according to both Amsterdam I/II and Bethesda guidelines, is reported in this study. The proband and some relatives of the patient have been investigated for whole genome sequencing, microsatellite instability, immunohistochemical MMR protein staining and verified by Sanger sequencing.

Results

A heterozygous insertion of uncertain significance (c.420dup, p.Met141Tyrfs) in MSH2 gene was found in proband (III-16) and part of His relatives. The variant was associated with a lack of expression of MSH2 protein (MMR deficient) and high microsatellite instability analysis (MSI) status in tumor tissues of LS patients. In addition, we found that the variant could affect the expression of MSH2 and the response to chemotherapy drugs in vitro.

Conclusion

We identified an insertion mutation (rs1114167810, c.420dup, p.Met141Tyrfs) in MSH2 in LS using whole genome-wide sequencing (WGS). We further confirmed that this mutation plays an important role in LS patients of this pedigree based on in vivo and vitro study.

Advances in Identification of Susceptibility Gene Defects of Hereditary Colorectal Cancer

Colorectal cancer (CRC) is a common malignant tumor of the digestive system worldwide, associated with hereditary genetic features. CRC with a Mendelian genetic predisposition accounts for approximately 5-10% of total CRC cases, mainly caused by a single germline mutation of a CRC susceptibility gene. The main subtypes of hereditary CRC are hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). With the rapid development of genetic testing methods, especially next-generation sequencing technology, multiple genes have now been confirmed to be pathogenic, including DNA repair or DNA mismatch repair genes such as APC, MLH1, and MSH2. Since familial CRC patients have poor clinical outcomes, timely clinical diagnosis and mutation screening of susceptibility genes will aid clinicians in establishing appropriate risk assessment and treatment interventions at a personal level. Here, we systematically summarize the susceptibility genes identified to date and the potential pathogenic mechanism of HNPCC and FAP development. Moreover, clinical recommendations for susceptibility gene screening, diagnosis, and treatment of HNPCC and FAP are discussed.

A Novel MLH1 Initiation Codon Mutation (c.3G>T) in a Large Chinese Lynch Syndrome Family with Different Onset Age and mRNA Expression Level

Lynch syndrome is a genetically and clinically heterogeneous disorder; it is caused by a germline mutation in DNA mismatch repair (MMR) genes. Individuals with a heterozygous mutation in MLH1 have an increased risk for developing colorectal cancer. Here we described a 5-generation Chinese Lynch syndrome family with different severity and onset age. A novel heterozygous germline mutation (c.3G>T, p.Met1Ile) in MLH1 gene was discovered by next generation sequencing. Our study also revealed by qPCR that the MLH1 mRNA expression in peripheral blood of patients in this family was remarkably lower than that of the unaffected carriers and non-carriers. The research results indicated that the mRNA expression level may provide predictive suggestions of treatment and management for carriers with the initiation codon mutation of MLH1 in this family. Further studies are undertaken in this family as well as other families with Lynch syndrome to interrogate the exact reasons affecting the MLH1 mRNA expression level and whether mRNA expression in peripheral blood could be a significant factor for early diagnosis and surveillance of Lynch syndrome.

Up-regulation of MSH6 is associated with temozolomide resistance in human glioblastoma

The impact of DNA mismatch repair (MMR) on resistance to temozolomide (TMZ) therapy in patients with glioblastoma (GBM) is recently reported but the mechanisms are not understood. We aim to analyze the correlation between MMR function and the acquired TMZ resistance in GBM using both relevant clinical samples and TMZ resistant cells. First we found increased expression of MSH6, one of key components of MMR, in recurrent GBM patients' samples who underwent TMZ chemotherapy, comparing with those matched samples collected at the time of diagnosis. Using the cellular models of acquired resistance to TMZ, we further confirmed the up-regulation of MSH6 in TMZ resistant cells. Moreover, a TCGA dataset contains a large cohort of GBM clinical samples with or without TMZ treatment reinforced the increased expression of MSH6 and other MMR genes after long-term TMZ chemotherapy, which may resulted in MMR dysfunction and acquired TMZ resistance. Our results suggest that increased expression of MSH6, or other MMR, may be a new mechanism contributing to the acquired resistance during TMZ therapy; and may serve as an indicator to the resistance in GBM.