Hereditary non-polyposis colorectal cancer (HNPCC): phenotype-genotype correlation between patients with and without identified mutation

Understanding familial risk of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease that is the result of an accumulation of sequential genetic alterations. These genetic alterations can either be inherited, such as pathogenic germline variants that are associated with an increased risk of cancer, or acquired, such as somatic mutations that occur during the lifetime of an individual. Understanding the genetic basis of inherited risk of PDAC is essential to advancing patient care and outcomes through improved clinical surveillance, early detection initiatives, and targeted therapies. In this review we discuss factors associated with an increased risk of PDAC, the prevalence of genetic variants associated with an increased risk in patients with PDAC, estimates of PDAC risk in carriers of pathogenic germline variants in genes associated with an increased risk of PDAC. The role of common variants in pancreatic cancer risk will also be discussed.

Familial Colorectal Cancer Type X

The genetic background is unknown for the 50-60% of the HNPCC families, who fulfill the Amsterdam criteria, but do not have a mutation in an MMR gene, and is referred to as FCCTX. This study reviews the clinical, morphological and molecular characteristics of FCCTX, and discusses the molecular genetic methods used to localize new FCCTX genes, along with an overview of the genes and chromosomal areas that possibly relate to FCCTX. FCCTX is a heterogeneous group, mainly comprising cases caused by single high-penetrance genes, or by multiple low-penetrance genes acting together, and sporadic CRC cases. FCCTX differs in clinical, morphological and molecular genetic characteristics compared to LS, including a later age of onset, distal location of tumours in the colon, lower risk of developing extracolonic tumours and a higher adenoma/carcinoma ratio, which indicates a slower progression to CRC. Certain characteristics are shared with sporadic CRC, e.g. similarities in gene expression and a high degree of CIN+, with significanly increased 20q gain in FCCTX. Other molecular characteristics of FCCTX include longer telomere length and hypomethylation of LINE-1, both being a possible explanation for CIN+. Some genes in FCCTX families (RPS20, BMPR1A, SEMA4A) have been identified by using a combination of linkage analysis and sequencing. Sequencing strategies and subsequent bioinformatics are improving fast. Exome sequencing and whole genome sequencing are currently the most promising tools. Finally, the involvement of CNV’s and regulatory sequences are widely unexplored and would be interesting for further investigation in FCCTX.

The analysis of a large Danish family supports the presence of a susceptibility locus for adenoma and colorectal cancer on chromosome 11q24

Hereditary colorectal cancer accounts for approximately 30% of all colorectal cancers, but currently only 5% of these families can be explained by highly penetrant, inherited mutations. In the remaining 25% it is not possible to perform a gene test to identify the family members who would benefit from prophylactic screening. Consequently, all family members are asked to follow a screening program. The purpose of this study was to localize a new gene which causes colorectal cancer. We performed a linkage analysis using data from a SNP6.0 chip in one large family with 12 affected family members. We extended the linkage analysis with microsatellites (STS) and single nucleotide polymorphisms (SNP's) and looked for the loss of heterozygosity in tumour tissue. Furthermore, we performed the exome sequencing of one family member and we sequenced candidate genes by use of direct sequencing. Major rearrangements were excluded after karyotyping. The linkage analysis with SNP6 data revealed three candidate areas, on chromosome 2, 6 and 11 respectively, with a LOD score close to two and no negative LOD scores. After extended linkage analysis, the area on chromosome 6 was excluded, leaving areas on chromosome 2 and chromosome 11 with the highest possible LOD scores of 2.6. Two other studies have identified 11q24 as a candidate area for colorectal cancer susceptibility and this area is supported by our results.

Outcome of genetic evaluation of patients with kidney cancer referred for suspected hereditary cancer syndromes

OBJECTIVE

To analyze patients with kidney cancer referred for evaluation at a high-volume genetics service at a comprehensive cancer center and identify factors associated with positive tests for hereditary cancer syndromes.

METHODS

A retrospective review of patients referred to the Clinical Genetics Service at Memorial Sloan-Kettering Cancer Center was performed, and patients with a personal history of kidney cancer were identified. Patient and disease characteristics were reviewed. In all, 4 variables including age at diagnosis of kidney tumor, presence of syndromic manifestations, family history of kidney cancer, and number of primary malignancies were evaluated for association with positive test results in 2 groups: patients tested for renal cell carcinoma syndromes and Lynch syndrome. Guidance for genetic testing strategy in patients with kidney cancer is provided.

RESULTS

Between 1999 and 2012, 120 patients with a history of kidney cancer were evaluated by the Clinical Genetics Service. The mean age at kidney cancer diagnosis was 52 years (interquartile range: 42-63), with 57% being women. A family history of kidney cancer was reported by 39 patients (33%). Time between diagnosis of first cancer and genetic consultation was <1 year in 54%, 2 to 5 years in 23%, and>5 years in the remaining 23%. Overall, 95 patients were tested for genetic abnormalities with 27 (28%) testing positive. Testing for renal cell carcinoma (RCC)-related syndromes was performed on 43 patients, with 13 testing positive (30%). Lynch syndrome testing was positive in 9 patients (32%) after 28 were tested. In RCC-associated syndromes, young age of diagnosis was associated with positive test results. Conversely, syndromic manifestations and increasing number of primary malignancies were associated with positive Lynch testing.

CONCLUSIONS

The discovery of inherited kidney cancer syndromes has provided a unique opportunity to identify patients at increased risk for cancer. Factors associated with positive genetic testing are unique to different syndromes. These data suggest that in kidney cancer patients evaluated for hereditary cancer syndromes, young age is associated with diagnosis of RCC syndromes, whereas syndromic manifestations and multiple primaries are found in Lynch syndrome. These results, along with clinical awareness, may be useful for practicing urologists to select patients with kidney cancer to refer for genetic counseling.

Functional examination of MLH1, MSH2, and MSH6 intronic mutations identified in Danish colorectal cancer patients

Background

Germ-line mutations in the DNA mismatch repair genes MLH1, MSH2, and MSH6 predispose to the development of colorectal cancer (Lynch syndrome or hereditary nonpolyposis colorectal cancer). These mutations include disease-causing frame-shift, nonsense, and splicing mutations as well as large genomic rearrangements. However, a large number of mutations, including missense, silent, and intronic variants, are classified as variants of unknown clinical significance.

Methods

Intronic MLH1, MSH2, or MSH6 variants were investigated using in silico prediction tools and mini-gene assay to asses the effect on splicing.

Results

We describe in silico and in vitro characterization of nine intronic MLH1, MSH2, or MSH6 mutations identified in Danish colorectal cancer patients, of which four mutations are novel. The analysis revealed aberrant splicing of five mutations (MLH1 c.588 + 5G > A, MLH1 c.677 + 3A > T, MLH1 c.1732-2A > T, MSH2 c.1276 + 1G > T, and MSH2 c.1662-2A > C), while four mutations had no effect on splicing compared to wild type (MLH1 c.117-34A > T, MLH1 c.1039-8 T > A, MSH2 c.2459-18delT, and MSH6 c.3439-16C > T).

Conclusions

In conclusion, we classify five MLH1/MSH2 mutations as pathogenic, whereas four MLH1/MSH2/MSH6 mutations are classified as neutral. This study supports the notion that in silico prediction tools and mini-gene assays are important for the classification of intronic variants, and thereby crucial for the genetic counseling of patients and their family members.

Criteria and prediction models for mismatch repair gene mutations: a review

One of the strongest predictors of colorectal cancer risk is carrying a germline mutation in a DNA mismatch repair (MMR) gene. Once identified, mutation carriers can be recommended for intensive screening that will substantially reduce their high colorectal cancer risk. Conversely, the relatives of carriers identified as non-carriers can be relieved of the burden of intensive screening. Criteria and prediction models that identify likely mutation carriers are needed for cost-effective, targeted, germline testing for MMR gene mutation. We reviewed 12 criteria/guidelines and 8 prediction models (Leiden, Amsterdam-plus, Amsterdam-alternative, MMRpro, PREMM1,2,6, MMRpredict, Associazione Italiana per lo studio della Familiarità ed Ereditarietà dei tumori Gastrointestinali (AIFEG) and the Myriad Genetics Prevalence table) for identifying mutation carriers. While criteria are only used to identify individuals with colorectal cancer (yes/no for screening followed by germline testing), all prediction models except MMRpredict and Myriad tables can predict the probability of carrying mutations for individuals with or without colorectal cancer. We conducted a meta-analysis of the discrimination performance of 17 studies that validated the prediction models. The pooled estimate for the area under curve was 0.80 (95% CI 0.72 to 0.88) for MMRpro, 0.81 (95% CI 0.73 to 0.88) for MMRpredict, 0.84 (95% CI 0.81 to 0.88) for PREMM, and 0.85 (95% CI 0.78 to 0.91) for Leiden model. Given the high degree of overlap in the CIs, we cannot state that one model has a higher discrimination than any of the others. Overall, the existing statistical models have been shown to be sensitive and specific (at a 5% cut-off) in predicting MMR gene mutation carriers. Future models may need to: provide prediction of PMS2 mutations, take into account a wider range of Lynch syndrome-associated cancers when assessing family history, and be applicable to all people irrespective of any cancer diagnosis.

Lynch or not Lynch? Is that always a question?

The familial cancer syndrome referred to as Lynch I and II was renamed hereditary nonpolyposis colorectal cancer (HNPCC) only to revert later to Lynch syndrome (LS). LS is the most frequent human predisposition for the development of colorectal cancer (CRC), and probably also for endometrial and gastric cancers, although it has yet to acquire a consensus name. Its estimated prevalence ranges widely from 2% to 7% of all CRCs due to the fact that tumors from patients with LS are difficult to recognize at both the clinical and molecular level. This review is based on two assumptions. First, all LS patients inherit a predisposition to develop CRC (without polyposis) and/or other tumors from the Lynch spectrum. Second, all LS patients have a germline defect in one of the DNA mismatch repair (MMR) genes. When a somatic second hit inactivates the relevant MMR gene, the consequence is instability of DNA repeat sequences such as microsatellites and the tumors are referred to as having the microsatellite instability (MSI) phenotype. However, some of the inherited predisposition to develop CRC without concurrent polyposis, termed HNPCC, is found in non-LS patients, while not all MSI tumors are from LS cases. LS tumors are therefore at the junction of inherited and MSI cases. We describe here the defining characteristics of LS tumors that differentiate them from inherited non-MSI tumors and from non-inherited MSI tumors.

A putative Lynch syndrome family carrying MSH2 and MSH6 variants of uncertain significance-functional analysis reveals the pathogenic one

Inherited pathogenic mutations in the mismatch repair (MMR) genes, MSH2, MLH1, MSH6, and PMS2 predispose to Lynch syndrome (LS). However, the finding of a variant or variants of uncertain significance (VUS) in affected family members complicates the risk assessment. Here, we describe a putative LS family carrying VUS in both MSH2 (c.2768T>A, p.Val923Glu) and MSH6 (c.3563G>A, p.Ser1188Asn). Two colorectal cancer (CRC) patients were studied for mutations and identified as carriers of both variants. In spite of a relatively high mean age of cancer onset (59.5 years) in the family, many CRC patients and the tumor pathological data suggested that the missense variation in MSH2, the more common susceptibility gene in LS, would be the predisposing alteration. However, MSH2 VUS was surprisingly found to be MMR proficient in an in vitro MMR assay and a tolerant alteration in silico. By supplying evidence that instead of MSH2 p.Val923Glu the MSH6 p.Ser1188Asn variant is completely MMR-deficient, the present study confirms the previous findings, and suggests that MSH6 (c.3563G>A, p.Ser1188Asn) is the pathogenic mutation in the family. Moreover, our results strongly support the strategy to functionally assess all identified VUS before predictive gene testing and genetic counseling are offered to a family.

Familial colorectal cancer: eleven years of data from a registry program in Switzerland

Deleterious germ-line variants involving the DNA mismatch repair (MMR) genes have been identified as the cause of the hereditary nonpolyposis colorectal cancer syndrome known as the Lynch syndrome, but in numerous familial clusters of colon cancer, the cause remains obscure. We analyzed data for 235 German-speaking Swiss families with nonpolyposis forms of colorectal cancer (one of the largest and most ethnically homogeneous cohorts of its kind) to identify the phenotypic features of forms that cannot be explained by MMR deficiency. Based on the results of microsatellite instability analysis and immunostaining of proband tumor samples, the kindreds were classified as MMR-proficient (n = 134, 57%) or MMR-deficient (n = 101, 43%). In 81 of the latter kindreds, deleterious germ-line MMR-gene variants have already been found (62 different variants, including 13 that have not been previously reported), confirming the diagnosis of Lynch syndrome. Compared with MMR-deficient kindreds, the 134 who were MMR proficient were less likely to meet the Amsterdam Criteria II regarding autosomal dominant transmission. They also had primary cancers with later onset and colon-segment distribution patterns resembling those of sporadic colorectal cancers, and they had lower frequencies of metachronous colorectal cancers and extracolonic cancers in general. Although the predisposition to colorectal cancer in these kindreds is probably etiologically heterogeneous, we were unable to identify distinct phenotypic subgroups solely on the basis of the clinical data collected in this study. Further insight, however, is expected to emerge from the molecular characterization of their tumors.

Spectrum of MLH1 and MSH2 mutations in Chilean families with suspected Lynch syndrome

PURPOSE

Lynch syndrome is the most common inherited syndrome of colorectal cancer, caused principally by germline mutations in MLH1 and MSH2. We report our experience with genetic screening in the diagnosis of Lynch syndrome in Chile, a country previously underserved in the capacity to diagnose hereditary colorectal cancer.

METHODS

Families from our Familial Colorectal Cancer Registry were selected for this study if they fulfilled either Amsterdam I/II or Bethesda criteria for classification of Lynch syndrome. Analysis of colorectal tumors from probands included a microsatellite instability study and immunohistochemical evaluation for MLH1 and MSH2. Screening of germline mutations was performed by single-strand conformation polymorphism analysis and DNA sequencing.

RESULTS

A total of 21 families were evaluated, 14 meeting Amsterdam criteria and 7 meeting Bethesda criteria. Tumors in 20 families (95%) showed microsatellite instability (19 high and 1 low) and 9 of these 20 families (45%) harbored a germline mutation (7 of 13 Amsterdam and 2 of 7 Bethesda families). Of the 9 mutations identified, 6 were in MLH1 and 3 in MSH2. Two of the mutations were novel, 3 were previously found in 1 to 2 European populations, and 4 were previously found in various ethnic populations worldwide. Only 2 mutations were previously found in another Latin American population (Colombia). In our probands, colorectal cancer was located mainly (57%) in the right or transverse colon. Pedigree information from 104 family affected members of 21 studied families showed endometrial cancer to be the most frequent primary extracolonic tumor, accounting for 15.1% of total cases, followed by stomach (13.2%) and breast cancer (11.3%). Analysis of mitochondrial DNA haplotypes showed a strong Amerindian genetic component in 15 (71.4%) of the 21 families analyzed.

CONCLUSION

The study of Lynch syndrome in families of different ethnic origins contributes to the definition of genetic and clinical differences among populations. Wide distribution in other ethnic populations strongly suggests varying origins of 4 the mutations found. Although cancer phenotype was consistent with those from other Latin American populations, only 2 of 9 mutations were shared with other South American populations and 2 novel mutations were found. The Chilean population is considered to be an admixture of Amerindian and European-mainly Spanish-populations, producing an ethnic group with significant genetic differences from populations previously studied.

The hMSH2 and hMLH1 genes in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common inherited colorectal cancer predisposing condition. HNPCC is an important problem for the surgeon because up to 60% of carriers of mismatch repair (MMR) gene mutations develop colorectal cancer (CRC), commonly before age 50 years. When CRC is diagnosed, the surgeon is in the ideal position to order appropriate tumor testing for microsatellite instability or immunohistochemical stains for loss of MMR gene associated protein, if this has not already been done. This article reviews the history of HNPCC, its clinical features, gene discovery, development of clinical genetic workup, and clinical surveillance, with an emphasis on the two major HNPCC genes, hMSH2 and hMLH1. It is not always possible to discuss these specific genes without commenting on the broader problem of HNPCC diagnosis and management.

Familial colorectal cancer type X: the other half of hereditary nonpolyposis colon cancer syndrome

Establishing the Amsterdam criteria, based on pedigrees, was essential for defining hereditary nonpolyposis colorectal cancer (HNPCC) syndrome in such a way that the underlying genetic cause could be identified. It is now known that about half of families that fulfill the original Amsterdam criteria have a hereditary DNA mismatch repair (MMR) gene mutation. These families may be said to have Lynch syndrome. The other half of families with HNPCC has no evidence of DNA MMR deficiency, and studies show that these families are different from families with Lynch syndrome. Familial colorectal cancer type X is the name used to refer to the "other half of HNPCC".

Functional characterization of rare missense mutations in MLH1 and MSH2 identified in Danish colorectal cancer patients

Recently, we have performed a population based study to analyse the frequency of colorectal cancer related MLH1 and MSH2 missense mutations in the Danish population. Half of the analyzed mutations were rare and most likely only present in the families where they were identified originally. Some of the missense mutations were located in conserved regions in the MLH1 and MSH2 proteins indicating a relation to disease development. In the present study, we functionally characterized 10 rare missense mutations in MLH1 and MSH2 identified in 13 Danish CRC families. To elucidate the pathogenicity of the missense mutations, we carried out in vitro functional analyses. The missense mutations were analyzed for their effect on protein expression and repair efficiency. The results of the functional analysis were correlated with clinical data on the families carrying these mutations. Eight missense mutations resulted in proteins with expression and repair efficiency similar to the wild type. One missense mutation (MSH2 p.Met688Val) caused reduced protein expression and one (MSH2 p.Leu187Arg) caused both reduced protein expression and repair deficiency. The MSH2 p.Leu187Arg mutation was found in an Amsterdam II family presenting with high microsatellite instability and loss of MSH2 and MSH6 proteins in tumours. In conclusion, only 1/10 missense mutations displayed repair deficiency and could be classified as pathogenic. No final conclusion can be drawn on the MSH2 p.Met688Val mutation, which caused reduced protein expression. Although, no deficiencies have been identified in the proteins harbouring the other missense mutations, pathogenicity of these variants cannot be unambiguously excluded.

Hereditary colorectal cancer: MYH-associated polyposis and other newly identified disorders

Historically, discussions of familial adenomatous polyposis and hereditary non-polyposis colon cancer have dominated lectures and writings on hereditary predisposition to colorectal cancer. In the last decade, the subject has grown well beyond the two entities. In this paper, five topics relevant to genetic risk assessment for colorectal cancer are reviewed. These include the autosomal recessive MYH-associated polyposis, hyperplastic polyposis and serrated pathway syndrome, the association of autosomal dominant juvenile polyposis with hereditary hemorrhagic telangiectasia, familial colorectal cancer type X, and the syndrome of biallelic DNA mismatch repair gene mutations. Knowledge of these entities may assist clinicians to recognize and manage cases that do not fit into the more common syndromes of colorectal cancer predisposition.

Genomic instability and carcinogenesis: an update

Cancers arise as a result of stepwise accumulation of mutations which may occur at the nucleotide level and/or the gross chromosomal level. Many cancers particularly those of the colon display a form of genomic instability which may facilitate and speed up tumor initiation and development. In few instances, a "mutator mutation" has been clearly implicated in driving the accumulation of other carcinogenic mutations. For example, the post-replicative DNA mismatch repair deficiency results in dramatic increase in insertion/deletion mutations giving rise to the microsatellite instability (MSI) phenotype and may predispose to a spectrum of tumours when it occurs in the germline. Although many sporadic cancers show multiple mutations suggesting unstable genome, the role of this instability in carcinogenesis, as opposed to the power of natural selection, has been a matter of controversy. This review gives an update of the latest data on these issues particularly recent data from genome-wide, high throughput techniques as well as mathematical modelling. Throughout this review, reference will be made to the relevance of genomic instability to the pathogenesis of colorectal carcinoma particularly its hereditary and familial subsets.

Major contribution from recurrent alterations and MSH6 mutations in the Danish Lynch syndrome population

An increasing number of mismatch-repair (MMR) gene mutations have been identified in hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome. This study presents the population-based Danish MMR gene mutation profile, which contains 138 different MMR gene alterations. Among these, 88 mutations in 164 families are considered pathogenic and an additional 50 variants from 76 families are considered to represent variants of unknown pathogenicity. The different MMR genes contribute to 40% (MSH2), 29% (MLH1), and 22% (MSH6) of the mutations and the Danish population thus shows a considerably higher frequency of MSH6 mutations than previously described. Although 69/88 (78%) pathogenic mutations were present in a single family, previously recognized recurrent/founder mutations were causative in 75/137 (55%) MLH1/MSH2 mutant families. In addition, the Danish MLH1 founder mutation c.1667+2_1667_+8TAAATCAdelinsATTT was identified in 14/58 (24%) MLH1 mutant families. The Danish Lynch syndrome population thus demonstrates that MSH6 mutations and recurrent/founder mutations have a larger contribution than previously recognized, which implies that the MSH6 gene should be included in routine diagnostics and suggests that directed analysis of recurrent/founder mutations may be feasible e.g. in families were diagnostic material is restricted to archival tissue.

The association between genetic variants in hMLH1 and hMSH2 and the development of sporadic colorectal cancer in the Danish population

BACKGROUND

Mutations in the mismatch repair genes hMLH1 and hMSH2 predispose to hereditary non-polyposis colorectal cancer (HNPCC). Genetic screening of more than 350 Danish patients with colorectal cancer (CRC) has led to the identification of several new genetic variants (e.g. missense, silent and non-coding) in hMLH1 and hMSH2. The aim of the present study was to investigate the frequency of these variants in hMLH1 and hMSH2 in Danish patients with sporadic colorectal cancer and in the healthy background population. The purpose was to reveal if any of the common variants lead to increased susceptibility to colorectal cancer.

METHODS

Associations between genetic variants in hMLH1 and hMSH2 and sporadic colorectal cancer were evaluated using a case-cohort design. The genotyping was performed on DNA isolated from blood from the 380 cases with sporadic colorectal cancer and a sub-cohort of 770 individuals. The DNA samples were analyzed using Single Base Extension (SBE) Tag-arrays. A Bonferroni corrected Fisher exact test was used to test for association between the genotypes of each variant and colorectal cancer. Linkage disequilibrium (LD) was investigated using HaploView (v3.31).

RESULTS

Heterozygous and homozygous changes were detected in 13 of 35 analyzed variants. Two variants showed a borderline association with colorectal cancer, whereas the remaining variants demonstrated no association. Furthermore, the genomic regions covering hMLH1 and hMSH2 displayed high linkage disequilibrium in the Danish population. Twenty-two variants were neither detected in the cases with sporadic colorectal cancer nor in the sub-cohort. Some of these rare variants have been classified either as pathogenic mutations or as neutral variants in other populations and some are unclassified Danish variants.

CONCLUSION

None of the variants in hMLH1 and hMSH2 analyzed in the present study were highly associated with colorectal cancer in the Danish population. High linkage disequilibrium in the genomic regions covering hMLH1 and hMSH2, indicate that common genetic variants in the two genes in general are not involved in the development of sporadic colorectal cancer. Nevertheless, some of the rare unclassified variants in hMLH1 and hMSH2 might be involved in the development of colorectal cancer in the families where they were originally identified.

Mismatch repair protein expression in Amsterdam II criteria-positive patients in Taiwan

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) is characterized genetically by germline mutations in DNA mismatch repair (MMR) genes. Immunohistochemistry (IHC) has high sensitivity and specificity for identifying MMR-deficient tumours. This study investigated the clinical presentations and frequency of HNPCC in Taiwan by combined Amsterdam II criteria (AC-II) and IHC.

METHODS

In 1995-2003, 7108 patients with primary colorectal cancer registered in Chang Gung Memorial Hospital's Colorectal Cancer Registry were screened using AC-II. Tumour specimens were analysed for MMR protein expression by IHC, and relevant clinicopathological details were documented.

RESULTS

Some 83 patients fulfilled the AC-II. Clinicopathologically, 43 patients (52 per cent) had proximal tumours, ten (12 per cent) had poorly differentiated cancers, 17 (20 per cent) had mucinous adenocarcinoma and 51 (61 per cent) had stage I-II tumours. Seventeen patients developed second primary colonic and extracolonic cancers over a mean 7.2-year follow-up. Immunohistochemically, 58 patients were MMR protein deficient. They had a significantly earlier age of onset (P < 0.001), more proximal tumour location (P = 0.002), less advanced tumour stage (P = 0.008) and more second primary cancers (P = 0.017) compared with MMR-competent patients.

CONCLUSION

These data show significant differences in clinical features between MMR protein-deficient and MMR competent subgroups.

Functional characterization of pathogenic human MSH2 missense mutations in Saccharomyces cerevisiae

Hereditary nonpolyposis colorectal cancer (HNPCC) is associated with defects in DNA mismatch repair. Mutations in either hMSH2 or hMLH1 underlie the majority of HNPCC cases. Approximately 25% of annotated hMSH2 disease alleles are missense mutations, resulting in a single change out of 934 amino acids. We engineered 54 missense mutations in the cognate positions in yeast MSH2 and tested for function. Of the human alleles, 55% conferred strong defects, 8% displayed intermediate defects, and 38% showed no defects in mismatch repair assays. Fifty percent of the defective alleles resulted in decreased steady-state levels of the variant Msh2 protein, and 49% of the Msh2 variants lost crucial protein-protein interactions. Finally, nine positions are predicted to influence the mismatch recognition complex ATPase activity. In summary, the missense mutations leading to loss of mismatch repair defined important structure-function relationships and the molecular analysis revealed the nature of the deficiency for Msh2 variants expressed in the tumors. Of medical relevance are 15 human alleles annotated as pathogenic in public databases that conferred no obvious defects in mismatch repair assays. This analysis underscores the importance of functional characterization of missense alleles to ensure that they are the causative factor for disease.

Novel MLH1 frameshift mutation in an extended hereditary nonpolyposis colorectal cancer family

AIM

To present novel frameshift mutation c.31delC [p.L11X] in the MLH1 gene identified in an extended Bulgarian hereditary non-polyposis colorectal cancer (HNPCC) family and to analyze the molecular and clinical findings within the pedigree concerning the proposal of adequate individual prophylactic strategy for all mutation carriers.

METHODS

The pedigree of the family consists of 42 members in four generations. Search for mutations in the MLH1 and hMSH2 genes was performed in the proband. After PCR amplification of all exons including flanking intronic regions, amplicons were directly sequenced.

RESULTS

The mutation was found in nine from the thirteen pedigree members who signed informed consent to participate in the study. In three adenocarcinomas, microsatellite instability and lack of the MLH1 protein expression were detected. The only one tubulovillous adenoma analyzed was microsatellite stable and the MLH1 protein showed an intact staining.

CONCLUSION

The newly described mutation c.31delC is HNPCC causative. Besides the typical clinical features of the syndrome, we found a specific pathologic manifestation such as moderate to high differentiated adenocarcinomas of the colon. One of the mutation carriers developed a benign giant cell soft tissue tumor. The primary tumor localizations were frequently extracolonic and detailed yearly gastrointestinal and gynecological examinations have been proposed to the mutation carriers. We emphasize the importance of including the HNPCC genetic counseling and testing as well in the following surveillance of all patients at risk in the services covered by the health insurance in Bulgaria.

Genotype-phenotype comparison of German MLH1 and MSH2 mutation carriers clinically affected with Lynch syndrome: a report by the German HNPCC Consortium

PURPOSE

Lynch syndrome is linked to germline mutations in mismatch repair genes. We analyzed the genotype-phenotype correlations in the largest cohort so far reported.

PATIENTS AND METHODS

Following standard algorithms, we identified 281 of 574 unrelated families with deleterious germline mutations in MLH1 (n = 124) or MSH2 (n = 157). A total of 988 patients with 1,381 cancers were included in this analysis.

RESULTS

We identified 181 and 259 individuals with proven or obligatory and 254 and 294 with assumed MLH1 and MSH2 mutations, respectively. Age at diagnosis was younger both in regard to first cancer (40 v 43 years; P < .009) and to first colorectal cancer (CRC; 41 v 44 years; P = .004) in MLH1 (n = 435) versus MSH2 (n = 553) mutation carriers. In both groups, rectal cancers were remarkably frequent, and the time span between first and second CRC was smaller if the first primary occurred left sided. Gastric cancer was the third most frequent malignancy occurring without a similarly affected relative in most cases. All prostate cancers occurred in MSH2 mutation carriers.

CONCLUSION

The proportion of rectal cancers and shorter time span to metachronous cancers indicates the need for a defined treatment strategy for primary rectal cancers in hereditary nonpolyposis colorectal cancer patients. Male MLH1 mutation carriers require earlier colonoscopy beginning at age 20 years. We propose regular gastric surveillance starting at age 35 years, regardless of the familial occurrence of this cancer. The association of prostate cancer with MSH2 mutations should be taken into consideration both for clinical and genetic counseling practice.

The genetics of HNPCC: application to diagnosis and screening

Hereditary nonpolyposis colorectal cancer syndrome (HNPCC; Lynch Syndrome) is the most common form of hereditary colorectal cancers. Predisposed individuals have increased lifetime risk of developing colorectal, endometrial and other cancers. The syndrome is primarily due to heterozygous germline mutations in one of the mismatch repair genes; mainly MLH1, MSH2, MSH6 and PMS2. The resulting mismatch repair deficiency leads to microsatellite instability which is the hallmark of tumors arising within this syndrome, as well as a variable proportion of sporadic tumors. Diagnostic guidelines and criteria for molecular testing of suspected families have been proposed and are continuously updated. However, not all families fulfilling these criteria show mutations in mismatch repair genes and/or microsatellite instability implicating other, as yet unknown, carcinogenic mechanisms and predisposition genes. This subset of tumors is the focus of current clinical and molecular research. This review addresses recent advances in the field of HNPCC research and their applications in the management of affected individuals and families.

Assessing the pathogenicity of MLH1 missense mutations in patients with suspected hereditary nonpolyposis colorectal cancer: correlation with clinical, genetic and functional features

Assessing the pathogenicity of missense mutations of MLH1 and MSH2 is critical to counsel patients with suspected hereditary nonpolyposis colorectal cancer (HNPCC). Approximately 32% of all MLH1 mutations and 18% of MSH2 mutations are missense variants which often have an uncertain genetic significance. To assess the pathogenicity of four MLH1 missense mutations which were found in five patients with suspected HNPCC, P648S (CCC --> TCC), L559R (CTG --> CGG), K618A (AAG --> GCG), Y646C (TAT --> TGT), we studied their ability to disrupt MLH1 protein function and their relationship with all those clinical, genetic and pathological features which are typical of this syndrome. Our results indicated that the P648S and L559R mutations were probably pathogenic because they disrupted MLH1 protein interaction with its partner PMS2 in vitro and abolished MLH1 expression in HCT116 cells. In addition these variants were associated with features often found in HNPCC patients: in particular high microsatellite instability, occurrence of high grade tumours and, in one case, strong family history. The pathogenicity of the K618A and Y646C mutations was questionable as their correlation with features typical of HNPCC was low and the outcome of the functional analysis was ambiguous. These observations suggested that a clinically usable assessment of the pathogenicity of MLH missense variants can be achieved through the analysis of multiple mutation characteristics among which loss of protein function, occurrence of microsatellite instability and family history seemed to have a predominant role.

Estimated prevalence of hereditary cancers and the need for surveillance in a Norwegian county, Telemark

OBJECTIVE

The aim of the study was to estimate the prevalence of hereditary cancers and the need for surveillance in Telemark county, Norway.

MATERIAL AND METHODS

All persons attending the Norwegian Colorectal Cancer Prevention (NORCCAP) trial in Telemark were interviewed about cases of cancer in the family. Diagnoses were verified, pedigrees constructed and families classified according to preset criteria aiming at identifying hereditary cancer. Mutation analyses were performed in kindreds at risk for breast cancers when possible. Immunohistochemistry of tumors in assumed inherited colorectal cancer families was undertaken.

RESULTS

The screening examination was attended by 7,224 persons among whom 2,866 had cancer in the family. Of these, 2,479 had no suspicion of any known inherited cancer syndrome. Family information questionnaires were mailed to 387 persons and returned by 191. Sixty-four of these 191 met the clinical criteria for familial cancer by family history after verification of diagnoses. Observed prevalences for being at risk for hereditary breast and breast-ovarian cancer (HBOC) or hereditary non-polyposis colorectal cancer (HNPCC) were 2.8 per thousand and 0.77 per thousand, respectively.

CONCLUSIONS

The number of colonoscopies and mammograms obtained per year serving those who needed them was limited and reduced by clinical genetic work-up from 2,866 with a family history of cancer to 64 proven cases. Continued surveillance of an unnecessarily high number leads to unjustified cancer worry, is costly and uses up health-care facilities. Genetic work-up is a one-time job that reduces input numbers to surveillance programs, provides a starting-point for mutation testing and is economically cost beneficial if inherited cancers are prevented or cured by the health-care programs offered.

Genetic counseling outcomes: perceived risk and distress after counseling for hereditary colorectal cancer

Genetic counseling may turn risk information into cancer prevention behavior by modifying health beliefs and cancer-related distress. We assessed the effect of genetic counseling on these factors in 101 adult first-degree-relatives of colorectal cancer patients from families with known or suspected hereditary nonpolyposis colorectal cancer. Before counseling and once afterward, subjects completed self-report measures of perceived lifetime risk and cancer-distress. Most persons overestimated their cancer risk, and higher perceived risk was associated with believing that colorectal cancer cannot be prevented. Individual perceived risk changed after counseling, although mean perceived risk was unchanged. After adjusting for baseline risk, older persons and those with higher estimated objective cancer risk had larger postcounseling decreases. Distress after counseling was positively correlated with baseline distress and anxiety symptoms, and inversely correlated with tolerance for ambiguity. The findings suggest counseling interventions that should increase the likelihood of screening and offer hypotheses for future research.

Functional significance and clinical phenotype of nontruncating mismatch repair variants of MLH1

BACKGROUND & AIMS

Germline mutations in mismatch repair genes are associated with hereditary nonpolyposis colorectal cancer. A significant proportion of mutations are nontruncating and associated with a variability of clinical phenotype and microsatellite instability and with occasional presence of residual protein in tumor tissue that suggests impaired functional activity but not total lack of mismatch repair. To address pathogenic significance and mechanism of pathogenicity, we studied the functionality of 31 nontruncating MLH1 mutations found in clinically characterized colorectal cancer families and 3 other variations listed in a mutation database.

METHODS

Mutations constructed by site-directed mutagenesis were studied for protein expression/stability, subcellular localization, protein-protein interaction, and repair efficiency. The genetic and biochemical data were correlated with clinical data. Finally, comparative sequence analysis was performed to assess the value of sequence homology as a tool for predicting functional results.

RESULTS

Altogether, 22 mutations were pathogenic in more than one assay, 2 variants were impaired in one assay, and 10 variants acted like wild-type protein. Twenty of 34 mutations affected the quantity of MLH1 protein, whereas only 15 mainly amino-terminal mutations were defective in an in vitro repair assay. Comparative sequence analysis correctly predicted functional studies for 82% of variants.

CONCLUSIONS

Pathogenic nontruncating alterations in MLH1 may interfere with different biochemical mechanisms but generally more than one. The severe biochemical defects are mirrored by phenotypic characteristics such as early age at onset and high microsatellite instability, whereas variants with no or mild defects in functionality are associated with variable clinical phenotypes.

Presymptomatic diagnosis using a deletion of a single codon in families with hereditary non-polyposis colorectal cancer

The diagnosis of hereditary non-polyposis colorectal cancer (HNPCC) is often confirmed by a mutation in one of several mismatch-repair genes, in particular MLH1, MSH2 and MSH6. Presymptomatic diagnosis requires the identification of a mutation causing the disease. Three different deletions of a single amino acid codon have previously been published as assumed pathogenic. The objective of this study was to determine if an MSH2 3 base pair in-frame deletion (N596del) could be used in presymptomatic screening of at-risk individuals. We report on five HNPCC families with the N596del mutation, identified after mutation screening of MSH2 and MLH1. All patients in the families were haplotyped using markers flanking the MSH2 gene. The haplotypes revealed that the five families with high probability descended from only two founders. The N596del segregated with the HNPCC phenotype with lod scores of 3.2 and 2.0 at the recombination fraction of 0.0 in the two founder families. Sequencing of MSH2 and MLH1 did not reveal other pathogenic mutations, and N596del was not identified in 50 healthy controls. The mutation has previously been found expressed in mRNA, and is located in a conserved domain. The results support the hypothesis that N596del is the disease causing mutation and not a clinically silent variation. On this basis, the application of the MSH2 N596del mutation, in presymptomatic screening of HNPCC families, is recommended.

Clinical phenotype and prevalence of hereditary nonpolyposis colorectal cancer syndrome in Chinese population

AIM: To describe systematically the clinical characteristics and phenotype of HNPCC families and the prevalence of HNPCC in the general population of CRC patients in China.

METHODS: HNPCC kindreds and CRC patients were from two sources. One was that we consecutively investigated kindreds and patients by ourselves. And the other was the published Chinese and foreign literature related to Chinese HNPCC syndrome. There were 142 HNPCC families fulfilling AC I and/or AC II including 57 families with detailed data, and 3874 general primary CRC patients in all. All statistical tests were two-sided.

RESULTS: In AC I families, the number of Lynch syndrome I and II families were 25 (47.2%) and 28 (52.8%) respectively. There were 215 patients (82.4%) with CRC, 67 patients (25.7%) with extracolonic cancer and 50 patients (19.2%) with multiple primary cancers. In all CRC patients, multiple primary CRC were in 41 patients (19.1%), and the first-CRC was right-sided colorectal cancer in 143 patients (66.5%) and rectal cancer in 44 patients (20.5%). 8.8% and 19.2% of the first cancer were CRC and extracolonic cancers. Among those patients whose first cancer was CRC, 66.8% and 19.9% were right-sided colorectal cancer and rectal cancer, respectively. The similar results were found in AC II families. Normal distribution was only found in the distribution of the age of diagnosis of the first cancer in both AC I families (coefficient of skewness: u = 0.81, 0.20<0.40<P<0.50; coefficient of kurtosis: u = 1.13, 0.20<P<0.40, α = 0.20) and AC II families (coefficient of skewness: u = 0.63, P>0.5>0.20; coefficient of kurtosis: u = 0.84, 0.20<0.40<P<0.50, α = 0.20), but not found in the distribution of the age of diagnosis of the first CRC. When patients with HNPCC-associated cancer suffered from the first malignant tumor in HNPCC families diagnosed by AC I and AC II, the mean age and median age were 45.1±12.7 years and 44.0 years, 45.2±12.7 years and 44.5 years, respectively. The median age of diagnosis of the first tumor of the patients in the later generation was younger than that in the previous generation. Many extracolonic cancers were found to be associated with HNPCC syndrome. Gastric cancer was the most frequent extracolonic cancer followed by endometrial cancer and hepatocarcinoma. In general population of CRC patients, the prevalence of HNPCC diagnosed by AC I and AC II were 1.3% and 2.2%, respectively.

CONCLUSION: The clinical phenotype and prevalence of Chinese HNPCC syndrome are similar to those of Europeans and Americans. Gastric cancer is the most common extracolonic malignant tumor. The age of diagnosis of the first malignant tumor tends to be increasingly younger in patients with HNPCC-related tumors.

High-throughput gene sequencing assay development for hereditary nonpolyposis colon cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common hereditary colon cancer syndrome and is responsible for as many as 10% of all colorectal cancers. Hereditary nonpolyposis colorectal cancer is autosomally dominant with a prevalence of 1 in 200-2000 and exhibits incomplete penetrance. Affected individuals have an approximately 70% lifetime risk of colon cancer with a mean age of onset of 44 years and an approximately 40% lifetime risk of endometrial cancer. At least 5 mismatch repair genes (MLH1, MSH2, MSH6, PMS1, PMS2) have been implicated in HNPCC; however, no predominant mutations were found in these genes. Mutation detection by direct sequencing has proven to be the most sensitive method. We have developed high-throughput full-length sequencing assays of the MLH1, MSH2, and MSH6 genes. These 3 genes account for approximately 90% of all germline mutations found in HNPCC. In our assays, 19 exons of MLH1, 16 exons of MSH2, 10 exons of MSH6, and the adjacent splice sites were amplified using polymerase chain reaction and loaded onto a capillary sequencing machine. Results were analyzed using sequence analysis software and stored in a relational database. Our assay method was validated using 15 affected patients and normal controls. It is anticipated that our high-throughput assay technique will provide accurate diagnoses for patients at risk for HNPCC and thereby facilitate early curative intervention.

Geno- and pheno-typic characterization in ten patients with double-primary gastric and colorectal adenocarcinomas

BACKGROUND AND AIMS

Although a number of double-primary gastric and colorectal cancers have been known to correlate with the mutator pathway, a possible association with known hereditary cancers regarding geno-pathogenesis has rarely been investigated. This study was intended to identify a possible association of hereditary cancers and the implications of the mutator or tumor-suppressor pathway in double-primary gastric and colorectal cancers.

MATERIALS AND METHODS

Fresh colorectal tissues and lymphocytes from ten patients with double-primary gastric and colorectal cancers were obtained consecutively. The mutator pathway was evaluated by detecting hMSH2 and hMLH1 mutations, microsatellite instability (MSI) using 12 microsatellite markers, and hMLH1 promoter region methylation. Protein expressions of hMSH2, hMLH1, APC, E-cadherin, and beta-catenin were identified by immune staining.

RESULTS

There was no pathogenic mutation in any introns or exons of hMSH2, hMLH1 or CDH1, and in exons 3, 5, 6, and 15 of CTNNB1. Either MSI or methylator phenotype was found in five gastric cancers and in four colorectal cancers. No patients met the Amsterdam criteria of hereditary nonpolyposis colorectal cancer (HNPCC) or its equivalent of hereditary gastric cancer. Two patients with gastric cancers among their first-degree relatives showed no E-cadherin expression. The two of the three patients with rectal cancers among their first-degree relatives showed mutator phenotype either in the gastric or in the colorectal cancer. A subset of double-primary gastric and colorectal cancers may thereby be categorized as variant forms of hereditary gastric or colorectal cancer. Both cytoplasmic and nuclear beta-catenins were expressed in all gastric and colorectal cancers. Among the gastric and colorectal cancers with either MSI or methylator phenotype, four of five gastric cancers showed both APC and E-cadherin expression, whereas one of four colorectal cancers showed them.

CONCLUSION

This may suggest that the mutator pathway and the aberrant tumor suppressor pathway of the APC-E-cadherin may be cooperative or separately activated in the geno-pathogenesis of double-primary gastric and colorectal cancers.

Extended microsatellite analysis in microsatellite stable, MSH2 and MLH1 mutation-negative HNPCC patients: genetic reclassification and correlation with clinical features

BACKGROUND

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder predisposing to predominantly colorectal cancer (CRC) and endometrial cancer frequently due to germline mutations in DNA mismatch repair (MMR) genes, mainly MLH1, MSH2 and also MSH6 in families seen to demonstrate an excess of endometrial cancer. As a consequence, tumors in HNPCC reveal alterations in the length of simple repetitive genomic sequences like poly-A, poly-T, CA or GT repeats (microsatellites) in at least 90% of the cases.

AIM OF THE STUDY

The study cohort consisted of 25 HNPCC index patients (19 Amsterdam positive, 6 Bethesda positive) who revealed a microsatellite stable (MSS)--or low instable (MSI-L)--tumor phenotype with negative mutation analysis for the MMR genes MLH1 and MSH2. An extended marker panel (BAT40, D10S197, D13S153, D18S58, MYCL1) was analyzed for the tumors of these patients with regard to three aspects. First, to reconfirm the MSI-L phenotype found by the standard panel; second, to find minor MSIs which might point towards an MSH6 mutation, and third, to reconfirm the MSS status of hereditary tumors. The reconfirmation of the MSS status of tumors not caused by mutations in the MMR genes should allow one to define another entity of hereditary CRC. Their clinical features were compared with those of 150 patients with sporadic CRCs.

RESULTS

In this way, 17 MSS and 8 MSI-L tumors were reclassified as 5 MSS, 18 MSI-L and even 2 MSI-H (high instability) tumors, the last being seen to demonstrate at least 4 instable markers out of 10. Among all family members, 87 malignancies were documented. The mean age of onset for CRCs was the lowest in the MSI-H-phenotyped patients with 40.5 +/- 4.9 years (vs. 47.0 +/- 14.6 and 49.8 +/- 11.9 years in MSI-L- and MSS-phenotyped patients, respectively). The percentage of CRC was the highest in families with MSS-phenotyped tumors (88%), followed by MSI-L-phenotyped (78%) and then by MSI-H-phenotyped (67%) tumors. MSS tumors were preferentially localized in the distal colon supposing a similar biologic behavior like sporadic CRC. MSH6 mutation analysis for the MSI-L and MSI-H patients revealed one truncating mutation for a patient initially with an MSS tumor, which was reclassified as MSI-L by analyzing the extended marker panel.

CONCLUSION

Extended microsatellite analysis serves to evaluate the sensitivity of the reference panel for HNPCC detection and permits phenotype confirmation or upgrading. Additionally, it confirms the MSS status of hereditary CRCs not caused by the common mutations in the MMR genes and provides hints to another entity of hereditary CRC.

Highly penetrant hereditary cancer syndromes

The past two decades have brought many important advances in our understanding of the hereditary susceptibility to cancer. Approximately 5-10% of all cancers are inherited, the majority in an autosomal dominant manner with incomplete penetrance. While this is a small fraction of the overall cancer burden worldwide, the molecular genetic discoveries that have resulted from the study of families with heritable cancer have not only changed the way these families are counselled and managed, but have shed light on molecular regulatory pathways important in sporadic tumour development as well. In this review, we consider 10 of the more highly penetrant cancer syndromes, with emphasis on those predisposing to breast, colon, and/or endocrine neoplasia. We discuss the prevalence, penetrance, and tumour spectrum associated with these syndromes, as well as their underlying genetic defects.

HNPCC mutation MLH1 P648S makes the functional protein unstable, and homozygosity predisposes to mild neurofibromatosis type 1

Heterozygous germ-line mutations in DNA mismatch repair (MMR) genes predispose individuals to hereditary nonpolyposis colorectal cancer (HNPCC), whereas with homozygous MMR gene mutations children are diagnosed at an early age with de novo neurofibromatosis type 1 (NF1) and/or hematological malignancies. Here, we describe a mutation, MLH1 P648S, which was found in a typical HNPCC family, with one homozygous child displaying mild features of NF1 and no hematological cancers. To evaluate the pathogenicity of the mutation, we studied both the expression and the function of the mutated protein. It generally has been assumed that the predisposing mutations prevent the production of a functional protein. The mutated MLH1 P648S protein was found to be unstable but still functional in mismatch repair, suggesting that the cancer susceptibility in the family and possibly also the mild disease phenotype in the homozygous individual are linked to shortage of the functional protein.

Current clinical selection strategies for identification of hereditary non-polyposis colorectal cancer families are inadequate: a meta-analysis

Present guidelines to identify hereditary non-polyposis colorectal cancer (HNPCC) families are criticized for limitations in accuracy. The Amsterdam criteria I and II (AC I and AC II) are used to predict a germline mutation in one of the mismatch repair genes. In families not fulfilling the AC I and AC II criteria, individual indications to test cancer specimens for microsatellite instability (MSI) are guided by the Bethesda Guidelines (BG). Germline mutation testing is then performed in patients who conform to the BG and show MSI. We investigated the sensitivity and specificity of AC I, AC II, and BG. A meta-analysis of studies on the value of the AC I and AC II criteria for predicting germline mutation, as well as a meta-analysis of BG for the detection of MSI was performed. For the AC I, sensitivity varied from 54 to 91% and specificity varied from 62 to 84%. For the AC II, the pooled sensitivity was 78% and specificity ranged between 46 and 68%. Post-test probabilities of a positive test result were 0.61 and 0.46 for the AC I and AC II, respectively. Post-test probabilities of a negative test result were 0.17 and 0.21 for the AC I and AC II, respectively. For the BG, the pooled sensitivity was 89% and pooled specificity was 53%. Post-test probability of a positive test result was 41%, and post-test probability of a negative test result was 9%. The sensitivity and specificity of the Amsterdam criteria for predicting a germline mutation that causes HNPCC is not sufficient. The BG are useful for the detection of MSI in a group of patients suspected of having familial colorectal cancer (CRC), but sensitivity is very low in the total group of newly diagnosed CRC patients. Therefore, a new strategy is needed for the identification of HNPCC.