Hereditary nonpolyposis colorectal cancer (Lynch syndromes I and II): a common genotype linked to oncogenes?

Prevalence and spectrum of DNA mismatch repair gene variation in the general Chinese population

Background

Identifying genetic disease-susceptible individuals through population screening is considered as a promising approach for disease prevention. DNA mismatch repair (MMR) genes including MLH1, MSH2, MSH6 and PMS2 play essential roles in maintaining microsatellite stability through DNA mismatch repair, and pathogenic variation in MMR genes causes microsatellite instability and is the genetic predisposition for cancer as represented by the Lynch syndrome. While the prevalence and spectrum of MMR variation has been extensively studied in cancer, it remains largely elusive in the general population. Lack of the knowledge prevents effective prevention for MMR variation–caused cancer. In the current study, we addressed the issue by using the Chinese population as a model.

Methods

We performed extensive data mining to collect MMR variant data from 18 844 ethnic Chinese individuals and comprehensive analyses for the collected MMR variants to determine its prevalence, spectrum and features of the MMR data in the Chinese population.

Results

We identified 17 687 distinct MMR variants. We observed substantial differences of MMR variation between the general Chinese population and Chinese patients with cancer, identified highly Chinese-specific MMR variation through comparing MMR data between Chinese and non-Chinese populations, predicted the enrichment of deleterious variants in the unclassified Chinese-specific MMR variants, determined MMR pathogenic prevalence of 0.18% in the general Chinese population and determined that MMR variation in the general Chinese population is evolutionarily neutral.

Conclusion

Our study provides a comprehensive view of MMR variation in the general Chinese population, a resource for biological study of human MMR variation, and a reference for MMR-related cancer applications.

Multi-center real-world comparison of the fully automated Idylla™ microsatellite instability assay with routine molecular methods and immunohistochemistry on formalin-fixed paraffin-embedded tissue of colorectal cancer

Microsatellite instability (MSI) is present in 15–20% of primary colorectal cancers. MSI status is assessed to detect Lynch syndrome, guide adjuvant chemotherapy, determine prognosis, and use as a companion test for checkpoint blockade inhibitors. Traditionally, MSI status is determined by immunohistochemistry or molecular methods. The Idylla™ MSI Assay is a fully automated molecular method (including automated result interpretation), using seven novel MSI biomarkers (ACVR2A, BTBD7, DIDO1, MRE11, RYR3, SEC31A, SULF2) and not requiring matched normal tissue. In this real-world global study, 44 clinical centers performed Idylla™ testing on a total of 1301 archived colorectal cancer formalin-fixed, paraffin-embedded (FFPE) tissue sections and compared Idylla™ results against available results from routine diagnostic testing in those sites. MSI mutations detected with the Idylla™ MSI Assay were equally distributed over the seven biomarkers, and 84.48% of the MSI-high samples had ≥ 5 mutated biomarkers, while 98.25% of the microsatellite-stable samples had zero mutated biomarkers. The concordance level between the Idylla™ MSI Assay and immunohistochemistry was 96.39% (988/1025); 17/37 discordant samples were found to be concordant when a third method was used. Compared with routine molecular methods, the concordance level was 98.01% (789/805); third-method analysis found concordance for 8/16 discordant samples. The failure rate of the Idylla™ MSI Assay (0.23%; 3/1301) was lower than that of referenced immunohistochemistry (4.37%; 47/1075) or molecular assays (0.86%; 7/812). In conclusion, lower failure rates and high concordance levels were found between the Idylla™ MSI Assay and routine tests.

The Prospective Lynch Syndrome Database reports enable evidence-based personal precision health care

The aims of the Prospective Lynch Syndrome Database (PLSD) are to provide empirical prospectively observed data on the incidences of cancer in different organs, survival following cancer and the effects of interventions in carriers of pathogenic variants of the mismatch repair genes (path_MMR) categorized by age, gene and gender. Although PLSD is assumption-free, as with any study the ascertainment procedures used to identify the study cohort will introduce selection biases which have to be declared and considered in detail in order to provide robust and valid results. This paper provides a commentary on the methods used and considers how results from the PLSD reports should be interpreted. A number of the results from PLSD were novel and some in conflict with previous assumptions. Notably, colonoscopic surveillance did not prevent colo-rectal cancer, survival after colo-rectal, endometrial and ovarian cancer was good, no survival gain was observed with more frequent colonoscopy, new causes of cancer-related death were observed in survivors of first cancers due to later cancers in other organs, variants in the different MMR genes caused distinct multi-cancer syndromes characterized by different penetrance and phenotypes. The www.PLSD.eu website together with the InSiGHT database website (https://www.insight-group.org/variants/databases/) now facilitate evidence-based personalized precision health care for individual carriers at increased risk of cancer. The arguments are summarized in a final discussion on how to conceptualize current knowledge for the different practical purposes of treating cancers, genetic counselling and prevention, and for understanding /research on carcinogenetic mechanisms.

History, genetics, and strategies for cancer prevention in Lynch syndrome

Colorectal cancer (CRC) is the most common gastrointestinal malignancy and the third cause of cancer death in men and women in the United States. The majority of CRC cases diagnosed annually are due to sporadic events, but up to 6% are attributed to known monogenic disorders that confer a markedly increased risk for the development of CRC and multiple extracolonic malignancies. Lynch syndrome is the most common inherited CRC syndrome and is associated with mutations in DNA mismatch repair genes, mainly MLH1 and MSH2 but also MSH6, PMS2, and EPCAM. Although the risk of CRC and endometrial cancer may approach near 75% and 50%, respectively, in gene mutation carriers, the identification of these individuals and at-risk family members through predictive genetic testing provides opportunities for cancer prevention including specialized cancer screening, intensified surveillance, and/or prophylactic surgeries. This article will provide a review of the major advances in risk assessment, molecular genetics, DNA mutational analyses, and cancer prevention and management made since Lynch syndrome was first described 100 years ago.

Hereditary nonpolyposis colorectal cancer (HNPCC)/Lynch syndrome

BACKGROUND

Hereditary nonpolyposis colorectal cancer HNPCC, Lynch syndrome) is a genetic disease of autosomal dominant inheritance. It is caused by a mutation in one of four genes of the DNA mismatch repair system and confers a markedly increased risk for various types of cancer, particularly of the colon and the endometrium. Its prevalence in the general population is about 1 in 500, and it causes about 2% to 3% of all colorectal cancers. Lynch syndrome is diagnosed in two steps: If it is suspected (because a patient develops cancer at an unusually young age or because of familial clustering), the tumor tissue is analyzed for evidence of deficient mismatch repair (microsatellite instability, loss of mismatch repair protein expression). If such evidence is found, a genetic mutation is sought. The identification of a pathogenic mutation confirms the diagnosis in the patient and enables predictive testing of other family members. Diagnostic evaluations for Lynch syndrome should be carried out with appropriate genetic counseling.

METHOD

Selective literature review.

RESULTS

Prospective cohort studies from Germany, Finland and the Netherlands have shown that colorectal cancers detected by systematic colonoscopic surveillance tend to be at an earlier stage than those that are discovered after the patients present with symptoms. The Finnish study also showed an overall reduction in cancer risk from colonoscopic polypectomy at regular intervals.

CONCLUSION

The studies conducted so far have not yet clearly documented the putative benefit of an individualized, risk-adapted surveillance strategy. Until this is done, patients with Lynch syndrome and healthy carriers of causative mutations should be monitored with annual colonoscopy and (for women) annual gynecological examination.

Genome dynamics in major bacterial pathogens

Pathogenic bacteria continuously encounter multiple forms of stress in their hostile environments, which leads to DNA damage. With the new insight into biology offered by genome sequences, the elucidation of the gene content encoding proteins provides clues toward understanding the microbial lifestyle related to habitat and niche. Campylobacter jejuni, Haemophilus influenzae, Helicobacter pylori, Mycobacterium tuberculosis, the pathogenic Neisseria, Streptococcus pneumoniae, Streptococcus pyogenes and Staphylococcus aureus are major human pathogens causing detrimental morbidity and mortality at a global scale. An algorithm for the clustering of orthologs was established in order to identify whether orthologs of selected genes were present or absent in the genomes of the pathogenic bacteria under study. Based on the known genes for the various functions and their orthologs in selected pathogenic bacteria, an overview of the presence of the different types of genes was created. In this context, we focus on selected processes enabling genome dynamics in these particular pathogens, namely DNA repair, recombination and horizontal gene transfer. An understanding of the precise molecular functions of the enzymes participating in DNA metabolism and their importance in the maintenance of bacterial genome integrity has also, in recent years, indicated a future role for these enzymes as targets for therapeutic intervention.

Evolution of the nomenclature for the hereditary colorectal cancer syndromes

The hereditary forms of colorectal cancer have been given many names historically as the manifestations have been gradually understood. Lynch syndrome has had several names, most prominently 'Hereditary Nonpolyposis Colorectal Cancer' or HNPCC. Clarification of the genetic basis and full phenotypic expression of this disease mandates a more clinically useful name that clarifies the consideration of non-colonic cancers in a family history, and unifies the diagnosis around the germline mutation in a DNA mismatch repair (MMR) gene. The term 'Lynch syndrome' is proposed for the autosomal dominant disease caused by a germline mutation in a DNA MMR gene.

Colorectal cancer and the relationship between genes and the environment

Colorectal cancer (CRC) is a significant cause of morbidity and mortality in developed countries, with both genetic and environmental factors contributing to the etiology and progression of the disease. Several risk factors have been identified, including positive family history, red meat intake, smoking, and alcohol intake. Protective factors include vegetables, calcium, hormone replacement therapy, folate, nonsteroidal anti-inflammatory drugs, and physical activity. The interaction between these environmental factors, in particular diet and genes, is an area of growing interest. Currently, oncogenes, tumor suppressor genes, and mismatch repair genes are believed to play an essential role in colorectal carcinogenesis. When considering the genetics of CRC, only 10% of cases are inherited and only 2-6% can be ascribed to the highly penetrant genes, such as APC, hMLH and hMSH2. Lower penetrance genes combined with a Western-style diet contribute to the majority of sporadic CRCs. The purpose of this article is to give a brief overview of the epidemiologic studies that have been conducted and present the major findings. Here, we examine the molecular events in CRC, with particular focus on the interaction between genes and environment, and review the most current research in this area.