The InSiGHT database: utilizing 100 years of insights into Lynch syndrome

This article provides a historical overview of the online database ( www.insight-group.org/mutations ) maintained by the International Society for Gastrointestinal Hereditary Tumours. The focus is on the mismatch repair genes which are mutated in Lynch Syndrome. APC, MUTYH and other genes are also an important part of the database, but are not covered here. Over time, as the understanding of the genetics of Lynch Syndrome increased, databases were created to centralise and share the variants which were being detected in ever greater numbers. These databases were eventually merged into the InSiGHT database, a comprehensive repository of gene variant and disease phenotype information, serving as a starting point for important endeavours including variant interpretation, research, diagnostics and enhanced global collection. Pivotal to its success has been the collaborative spirit in which it has been developed, its association with the Human Variome Project, the appointment of a full time curator and its governance stemming from the well established organizational structure of InSiGHT.

Epigenetic mechanisms in the pathogenesis of Lynch syndrome

Inherited defects in the DNA mismatch repair (MMR) system, MLH1, MSH2, MSH6, and PMS2 genes, underlie Lynch syndrome, one of the most prevalent cancer syndromes in man. The syndrome offers a model for cancers arising through MMR defects and microsatellite instability, which applies to ~ 15% of all colorectal, endometrial, and other cancers. Lynch syndrome also illustrates the significance of the epigenetic component in cancer development. Inactivation of tumor suppressor genes by epigenetic mechanisms is an acquired property of many tumors developing in Lynch syndrome. Furthermore, constitutional epimutations of MMR genes may explain a proportion of mutation-negative families lacking MLH1 or MSH2 protein expression in tumor tissue. This review provides an update of the molecular basis of Lynch syndrome by focusing on the role of epigenetic mechanisms in the pathogenesis of the disease.

Direct contact in inviting high-risk members of hereditary colon cancer families to genetic counselling and DNA testing

BACKGROUND

Identification of hereditary predisposition to cancer has limited significance if not followed by efficient cancer prevention in the family. Probands are traditionally left to inform their relatives about the increased risk, but distant relatives may remain uninformed. An approach to contacting directly at-risk persons assumed to be unaware of their increased cancer risk was taken. With cancer prevention as the ultimate goal, the study was aimed at investigating attitudes towards and psychosocial consequences of this novel strategy.

METHODS

In families with hereditary non-polyposis colorectal cancer (Lynch syndrome), 286 healthy adult relatives with a 50% risk of a predisposing mutation were contacted by letter. Of these, 112 participated in counselling and predictive testing. Baseline information and information obtained 1 month after the test for 73 respondents were compared with 299 corresponding subjects, approached via the proband (family-mediated approach in our previous study) in these families.

RESULTS

After the contact letter, 51% consented to the study. Of these, 92% approved of the direct contact and 33% had tried to seek information. In 34% of the mutation carriers, neoplasia was identified in the first post-test colonoscopy. Although post-test fear of cancer increased among the mutation carriers and decreased among noncarriers, almost all participants were satisfied with their decision to participate, independently of their test results, parallel to the family-mediated approach.

CONCLUSION

In this large-scale study, relatives in cancer families were actively contacted to inform them of the condition and genetic counselling. Their attitudes were encouraging, and the psychosocial consequences were similar to the family-mediated approach. Our results suggest the appropriateness of direct contact as an alternative method of contact in cases of life-threatening treatable disease.

Is gastric cancer part of the tumour spectrum of hereditary non-polyposis colorectal cancer? A molecular genetic study

BACKGROUND

Gastric cancer is the second most common extracolonic malignancy in individuals with hereditary non-polyposis colorectal cancer (HNPCC)/Lynch syndrome. As gastric cancer is relatively common in the general population as well, it is not clear whether or not gastric cancer is a true HNPCC spectrum malignancy.

AIM

To determine whether or not gastric cancer is a true HNPCC spectrum malignancy.

SUBJECTS AND METHODS

The molecular and clinicopathological profiles of gastric cancers (n = 13) from HNPCC mutation carriers were evaluated and compared with the profiles of sporadic gastric cancers (n = 46) stratified by histology and microsatellite instability (MSI) status.

RESULTS

This study on sporadic and HNPCC gastric cancers revealed several important universal associations. Loss of heterozygosity in the adenomatous polyposis coli (APC) region was associated with intestinal histology regardless of the MSI (p = 0.007). KRAS-mutations (p = 0.019) and frameshift mutations in repeat tracts of growth-regulatory genes (p<0.001) were associated with MSI tumours being absent in microsatellite stable (MSS) tumours. The average number of methylated tumour suppressor gene loci among the 24 genes studied (methylation index) was higher in MSI than in MSS tumours regardless of histology (p<0.001). Gastric cancers from HNPCC mutation carriers resembled sporadic intestinal MSI gastric cancers, except that MLH1 promoter methylation was absent (p<0.001) and the general methylation index was lower (p = 0.038), suggesting similar, but not identical, developmental pathways. All these lacked the mismatch repair protein corresponding to the germline mutation and displayed high MSI.

CONCLUSION

The present molecular evidence, combined with the previous demonstration of an increased incidence relative to the general population, justify considering gastric cancers as true HNPCC spectrum malignancies.

Mechanisms of inactivation of MLH1 in hereditary nonpolyposis colorectal carcinoma: a novel approach

Mutations in the DNA mismatch repair gene MLH1 are a major cause of hereditary nonpolyposis colorectal cancer (HNPCC). No mutant phenotype is observed before the wild-type (wt) allele is somatically inactivated in target tissue. We addressed the mechanisms of MLH1 inactivation in 25 colorectal (CRC) and 32 endometrial cancers (ECs) from MLH1 mutation carriers (Mut1, in-frame genomic deletion; Mut2, out-of-frame splice site mutation; Mut3, missense mutation). By a quantitative method, matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF), utilizing four intragenic single nucleotide polymorphisms and mutations, loss of heterozygosity (LOH) was present in 31/57 (54.4%) of tumors. The wt allele displayed LOH more often than the mutant allele (23/57 vs 8/57, P=0.006). For Mut1, LOH was more frequent in CRC than EC (10/11 vs 1/13, P<0.0001), whereas Mut2 and Mut3 displayed opposite LOH pattern. Moreover, although wt LOH predominated in CRC irrespective of the predisposing mutation, LOH often affected the mutant allele in EC from Mut2 and Mut3 carriers (6/19, 31.6%). MLH1 promoter methylation, which reflected a more widespread hypermethylation tendency, occurred in 4/55 (7.3%) of tumors and was inversely associated with LOH. In conclusion, the patterns of somatic events (LOH and promoter methylation) differ depending on the tissue and germline mutation, which may in part explain the differential tumor susceptibility of different organs in HNPCC. MALDI-TOF provides a novel approach for the detection and quantification of LOH.

Linkage analysis in a large Swedish family supports the presence of a susceptibility locus for adenoma and colorectal cancer on chromosome 9q22.32-31.1

BACKGROUND

The best known hereditary colorectal cancer syndromes, familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), constitute about 2% of all colorectal cancers, and there are at least as many non-FAP, non-HNPCC cases where the family history suggests a dominantly inherited colorectal cancer risk. Recently, a locus on chromosome 9q22.2-31.2 was identified by linkage analysis in sib pairs with colorectal cancer or adenoma.

METHODS

Linkage analysis for the suggested locus on chromosome 9 was carried out in an extended Swedish family. This family had previously been investigated but following the identification of adenomas in several previously unaffected family members, these subjects were now considered to be gene carriers.

RESULTS

In the present study, we found linkage of adenoma and colorectal cancer to chromosome 9q22.32-31.1 with a multipoint LOD score of 2.4. We were also able to define the region for this locus to 7.9 cM between the markers D9S280 and D9S277.

CONCLUSIONS

Our result supports the presence of a susceptibility locus predisposing to adenoma and colorectal cancer in this chromosomal region.

BRAF screening as a low-cost effective strategy for simplifying HNPCC genetic testing

BACKGROUND

According to the international criteria for hereditary non-polyposis colorectal cancer (HNPCC) diagnostics, cancer patients with a family history or early onset of colorectal tumours showing high microsatellite instability (MSI-H) should receive genetic counselling and be offered testing for germline mutations in DNA repair genes, mainly MLH1 and MSH2. Recently, an oncogenic V600E hotspot mutation within BRAF, a kinase encoding gene from the RAS/RAF/MAPK pathway, has been found to be associated with sporadic MSI-H colon cancer, but its association with HNPCC remains to be further clarified.

METHODS

BRAF-V600E mutations were analysed by automatic sequencing in colorectal cancers from 206 sporadic cases with MSI-H and 111 HNPCC cases with known germline mutations in MLH1 and MSH2. In addition, 45 HNPCC cases showing abnormal immunostaining for MSH2 were also analysed.

RESULTS

The BRAF-V600E hotspot mutation was found in 40% (82/206) of the sporadic MSI-H tumours analysed but in none of the 111 tested HNPCC tumours or in the 45 cases showing abnormal MSH2 immunostaining.

CONCLUSIONS

Detection of the V600E mutation in a colorectal MSI-H tumour argues against the presence of a germline mutation in either the MLH1 or MSH2 gene. Therefore, screening of these mismatch repair (MMR) genes can be avoided in cases positive for V600E if no other significant evidence, such as fulfilment of the strict Amsterdam criteria, suggests MMR associated HNPCC. In this context, mutation analysis of the BRAF hotspot is a reliable, fast, and low cost strategy which simplifies genetic testing for HNPCC.

Ethnic variation in the prevalence of AZF deletions in testicular cancer

Seventy-six percent of testicular cancers of origin in Finns have been reported to exhibit AZF deletions. We analyze here 40 testicular tumor cases from Norway and Argentina and we found that AZF deletions occur also in non-Finnish cases but at significantly lower frequency (25%) than in Finland testicular tumor cases. This frequency difference can be attributed to the condition of genetic isolate of the Finnish population and the subsequent prevalence in this ethnic group of genetic factors involved in the origin of AZF deletions associated with malignancies. The finding of a correlation between AZF deletions and a given Y haplogroup would indicate the existence of Y lineages carrying AZF deletion-enhancing gene or genes. This possibility was explored using a set of Y-DNA-markers allowing the identification of Y lineages occurring at high frequency in Finns. We characterized the Y haplogroups in 32 normal Finn males (control group) and 17 cases of testicular cancer in Finns with and without AZF deletions. We found no association between Y lineages and AZF microdeletions, nor between AZF microdeletions and a Y microdeletion (DYS7C) exhibiting high prevalence (>50%) in Finns. The lack of correlation between AZF deletions and Y haplogroups indicates that the origin of these deletions is independent from the Y chromosome genetic background. No AZF deletions were found in familial cases of testicular tumors; hence, hereditary factors inducing the appearance of testicular malignancies in certain genealogies apparently do not increase the susceptibility to AZF deficiencies. AZF deletions are de novo events occurring in prezygotic or in post-zygotic stages. We propose that most AZF deletions associated with testicular tumors are due to post-zygotic Y microdeletions, while most cases of deletions associated with infertility are due to deletions occurring in the germ cell line of proband fathers.

Genotype and phenotype in hereditary nonpolyposis colon cancer: a study of families with different vs. shared predisposing mutations

Hereditary nonpolyposis colorectal cancer (HNPCC) is a multi-organ cancer syndrome associated with heritable mutations in DNA mismatch repair genes, particularly MLH1 (MutL Homologue 1) and MSH2 (MutS Homologue 2). We took advantage of the unique characteristics of the Finnish HNPCC families to assess genotype- phenotype correlations in this disorder. We studied 295 mutation carriers (10 mutations in MLH1 and 3 in MSH2) segregating in 55 families. In addition to the comparison of families with different mutations, the enrichment of two MLH1 mutations, one affecting exon 16 (29 families, 186 individuals) and another one affecting exon 6 (10 families, 45 individuals) allowed the comparison of kindreds with identical predisposing mutations. Extracolonic cancers were more common in MSH2 than MLH1 mutation carriers, with the ratios of 0.48 and 0.64, respectively, of colorectal cancer to all cancers (P = 0.076). Within MLH1, two mutations affecting only the amino terminal portion showed a significant association with late onset of cancer as compared to the remaining mutations. Importantly, families with the MLH1 exon 16 mutation displayed significant variation (P = 0.012) in the age at onset of colon cancer, despite shared predisposition. We conclude that even though characteristics of the inherited mutations may explain part of the observed clinical variation, other factors have a significant impact on HNPCC phenotype determination.

Genotype and phenotype in hereditary nonpolyposis colon cancer: a study of families with different vs. shared predisposing mutations

Hereditary nonpolyposis colorectal cancer (HNPCC) is a multi-organ cancer syndrome associated with heritable mutations in DNA mismatch repair genes, particularly MLH1 (MutL Homologue 1) and MSH2 (MutS Homologue 2). We took advantage of the unique characteristics of the Finnish HNPCC families to assess genotype- phenotype correlations in this disorder. We studied 295 mutation carriers (10 mutations in MLH1 and 3 in MSH2) segregating in 55 families. In addition to the comparison of families with different mutations, the enrichment of two MLH1 mutations, one affecting exon 16 (29 families, 186 individuals) and another one affecting exon 6 (10 families, 45 individuals) allowed the comparison of kindreds with identical predisposing mutations. Extracolonic cancers were more common in MSH2 than MLH1 mutation carriers, with the ratios of 0.48 and 0.64, respectively, of colorectal cancer to all cancers (P = 0.076). Within MLH1, two mutations affecting only the amino terminal portion showed a significant association with late onset of cancer as compared to the remaining mutations. Importantly, families with the MLH1 exon 16 mutation displayed significant variation (P = 0.012) in the age at onset of colon cancer, despite shared predisposition. We conclude that even though characteristics of the inherited mutations may explain part of the observed clinical variation, other factors have a significant impact on HNPCC phenotype determination.

Genetic and clinical characterisation of familial adenomatous polyposis: a population based study

BACKGROUND

Familial adenomatous polyposis (FAP) is a rare autosomal dominantly inherited disease predisposing to colon cancer and caused by germline mutations in the APC (adenomatous polyposis coli) gene.

AIMS

We conducted a population based study to evaluate the prevalence and clinical implications of APC mutations among Finnish FAP kindreds. A possible founder effect in parallel with previous observations in hereditary non-polyposis colon cancer (HNPCC) was addressed.

PATIENTS

Affected individuals from 65 kindreds were included.

METHODS

The APC gene was screened for mutations using the protein truncation test and heteroduplex analysis. Haplotype analysis was performed with four flanking microsatellite markers. Families that failed to show any mutations were scrutinised with Southern blot hybridisation and allelic expression analysis.

RESULTS

Thirty eight different germline mutations in APC were identified in 47 kindreds (72%). The majority of these mutations were novel and unique to each family. Although sharing the classical polyposis phenotype, families without detectable APC mutations differed from mutation positive families in the following respects: firstly, mean age at polyposis diagnosis was higher (38.6 years (48 individuals) v 30.0 years (140 individuals); p=0.001); and secondly, the proportion of kindreds lacking extracolonic disease was higher (6/18 v. 5/47; p=0.04).

CONCLUSIONS

Our results may pave the way for predictive testing in mutation positive families and should stimulate further molecular studies in mutation negative families. No founder effect was observed, which is in contrast with HNPCC in the same population.

The role of hPMS1 and hPMS2 in predisposing to colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is attributable to a deficiency of mismatch repair. Inactivation of DNA mismatch repair underlies the genesis of microsatellite instability in colorectal cancer. Germline mutations in three DNA mismatch repair genes, hMSH2, hMLH1, and hMSH6, have been found to segregate in HNPCC and HNPCC-like families. The two DNA mismatch repair genes hPMS1 and hPMS2 have also been suggested to predispose to HNPCC. In this study, 84 HNPCC and HNPCC-like kindreds without known mutations in the other three known DNA mismatch repair genes were screened for germline mutations in the hPMS1 or hPMS2 gene. No clear-cut pathogenic mutations were identified. Conversion technology was used to detect a large hMSH2 deletion in two affected members of the kindred in which the hPMS1 mutation was originally reported, whereas the hPMS1 mutation was only present in one of these two individuals. Since the hPMS1 and hPMS2 genes were first reported, germline mutations in hPMS2 have been demonstrated primarily in patients with Turcot's syndrome. However, no mutation in any of the two genes has been found to segregate in HNPCC families. Until there is better evidence for an increased colorectal cancer risk associated with germline mutations in these genes, a conservative interpretation of the role of mutations in these genes is advised.

Molecular screening for hereditary nonpolyposis colorectal cancer: a prospective, population-based study

PURPOSE

Germline mutations in mismatch repair genes predispose to hereditary nonpolyposis colorectal cancer (HNPCC). To address effective screening programs, the true incidence of the disease must be known. Previous clinical investigations reported estimates ranging between 0.5% and 13% of all the colorectal cancer (CRC) cases, whereas biomolecular studies in Finland found an incidence of 2% to 2.7% of mutation carriers for the disease. The aim of the present report is to establish the frequency of the disease in a high-incidence area for colon cancer.

PATIENTS AND METHODS

Through the data of the local CRC registry, we prospectively collected all cases of CRC from January 1, 1996, through December 31, 1997 (N = 391). Three hundred thirty-six CRC cases (85.9% of the incident cases) were screened for microsatellite instability (MSI) with six to 12 mono- and dinucleotide markers. MSI cases were subjected to MSH2 and MLH1 germline mutation analysis and immunohistochemistry; the methylation of the promoter region was studied for MLH1.

RESULTS

Twenty-eight cases (8.3% of the total) showed MSI. MSI cases differed significantly from microsatellite-stable (MSS) cases for their proximal location (P <.01), high mucinous component (P <.01), and poor differentiation (P =.002). Of MSI cases studied (n = 12), only one with a family history compatible with HNPCC had a germline mutation (in MSH2). Five other patients with a family history of HNPCC (two with MSI and three with MSS tumors) did not show germline mutations.

CONCLUSION

We conclude that the incidence of molecularly confirmed HNPCC (one [0.3%] of 336) in a high-incidence area for CRC is lower than in previous biomolecular and clinical estimates.

CYCLIN D1 as a genetic modifier in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer is associated with inherited defects in DNA mismatch repair. Clinical variation even in cases with identical predisposing mutations suggests the existence of other factors contributing to the phenotype. We addressed the modifying role of the common A/G polymorphism in exon 4 and the alternatively spliced transcripts a and b of the CCND1 gene encoding cyclin D1 in a series of 146 affected carriers of 10 MLH1 and 3 MSH2 mutations. No correlation was observed between a particular allele (A versus G) and age at onset. However, the presence of the variant transcript b in blood/normal mucosa, by multiplex reverse transcription-PCR, was associated with a significantly lower age at onset of colon cancer as compared with individuals with transcript a only (35 versus 46 years; P = 0.02). Whereas our data do not support a modifying role of A versus G allele of CCND1, the results do suggest that the relative abundance of a and b transcripts may modify the age at onset of colon cancer in hereditary nonpolyposis colorectal cancer.

Deficient DNA mismatch repair: a common etiologic factor for colon cancer

Hereditary non-polyposis colon cancer (HNPCC), the most common form of hereditary colon cancer, is a syndrome of deficient DNA mismatch repair (MMR). Five, possibly six, human MMR genes have been identified that, when mutated in the germline, cause susceptibility to this syndrome. To date, more than 300 different predisposing mutations are known, mainly affecting the MMR genes MLH1 ( approximately 50%), MSH2 ( approximately 40%) and MSH6 ( approximately 10%). Genetically predisposed individuals carry a defective copy of an MMR gene in every cell. Somatic inactivation of the remaining wild-type copy in a target tissue, typically colon, gives rise to a profound repair defect, progressive accumulation of mutations and cancer. Instability at short tandem repeat sequences, microsatellites, is a typical manifestation of MMR deficiency and apart from HNPCC tumors, occurs in approximately 15% of sporadic colon and other tumors. The majority of the latter cases are attributable to one particular MMR gene, MLH1, and unlike HNPCC, an epigenetic rather than a genetic mechanism plays an important role in the inactivation of this gene. The present review provides an update of the genetics of HNPCC and more generally, of cancer development driven by deficient MMR. Recent discoveries suggest that apart from post-replication repair, MMR proteins have several other functions that are highly relevant to carcinogenesis. Knowledge of the complex interplay between the MMR system and other cellular pathways allows us to better understand the phenotypic manifestations of HNPCC and other cancers with deficient MMR.

Lack of MSH2 and MSH6 characterizes endometrial but not colon carcinomas in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer syndrome is associated with an inherited predisposition to primarily colorectal cancer (CRC) and endometrial cancer (EC); however, the biological basis of the organ involvement remains unknown. As an attempt to explore whether the expression levels of MLH1, MSH2, and MSH6 may play a role, we used immunohistochemistry to study 42 ECs and 35 CRCs from patients carrying the same predisposing mutations. Among MSH2 mutation carriers, MLH1 was expressed in both tumor types, whereas MSH2 and, in many cases, also MSH6, were absent. Remarkably, among MLH1 mutation carriers, 54% of ECs (21 of 39), but none of the CRCs (0 of 32), lacked the MSH2 and/or MSH6 protein in addition to lacking MLH1 protein expression. These results demonstrate a marked difference between hereditary nonpolyposis colorectal cancer-related CRCs and ECs and suggest that the development of the latter tumors is selectively associated with the MSH2/MSH6 protein complex deficiency.

DNA mismatch repair and cancer

Five human DNA mismatch repair genes have been identified that, when mutated, cause susceptibility to hereditary nonpolyposis colorectal cancer (HNPCC). Mutational inactivation of both copies of a DNA mismatch repair gene results in a profound repair defect and progressive accumulation of mutations throughout the genome. Some of the mutations confer selective advantage on the cells, giving rise to cancer. Recent discoveries suggest that apart from postreplication repair, DNA mismatch repair proteins have several other functions that are highly relevant to carcinogenesis. These include DNA damage surveillance, prevention of recombination between nonidentical sequences and participation in meiotic processes (chromosome pairing). A brief overview of these different features of the human DNA mismatch repair system will be provided, with the emphasis in their implications in cancer development.

MSH6 and MSH3 are rarely involved in genetic predisposition to nonpolypotic colon cancer

A set of 90 nonpolypotic colon cancer families in which germ-line mutations of MSH2 and MLH1 had been excluded were screened for mutations in two additional DNA mismatch repair genes, MSH6 and MSH3. Kindreds fulfilling and not fulfilling the Amsterdam I criteria, showing early and late onset colorectal (and other) cancers, and having microsatellite stable and unstable tumors were included. Two partly parallel approaches were used: genetic linkage analysis (19 large families) and the protein truncation test (85, mostly smaller, families). Whereas MSH3 was not involved in any family, a large Amsterdam-positive, late-onset family showed a novel germ-line mutation in MSH6 (deletion of CT at nucleotide 3052 in exon 4). The mutation was identified through genetic linkage (multipoint lod score 2.4) and subsequent sequencing of MSH6. Furthermore, the entire MSH6 gene was sequenced exon by exon in families with frameshift mutations in the (C)8 tract in tumors, previously suggested as a predictor of MSH6 germ-line mutations; no mutations were found. We conclude that germ-line involvement of MSH6 and MSH3 is rare and that other genes are likely to account for a majority of MSH2-, MLH1-mutation negative families with nonpolypotic colon cancer.

Nuclear and mitochondrial genome instability in human breast cancer

We analyzed 40 pairs of breast normal/cancer tissues for the presence of mitochondrial (mt) genome instability and nuclear MSI in tumor cells. As mt, markers we used a (CA)n mt microsatellite (MS) starting at the 514-bp position of the D loop region and 4 informative MnlI sites located between the 16,108- and 16,420-bp positions of the D loop region. Nuclear microsatallite instability (MSI) was tested with 8 (CA)n MS, syntenic for the 13q chromosome arm. Moreover, we tested the spontaneous frequency of mtMSI and mt-MnlI mutations in 459 mother/descendant events. Mutations of mt-MnlI sites were found in 19 of 40 (47.5%) breast tumors, representing a 216-fold increase over the spontaneous rate in the female germline. Instability of the mtMS occurred in 17 of 40 (42.5%) breast cancers, which implies a 16-fold increase over the rate of spontaneous mutations. Nuclear MSI was found in 20 of 40 (50%) cases. In 15 of these cases the MSI was restricted to one locus, whereas in 5 instances the change of alleles was detected in 2 or 3 loci. Analysis of the correlation between mt and nuclear mutations showed no significant associations, suggesting that different systems are responsible for mt and nuclear genome instability in tumor cells. We propose that the two main mechanisms producing mtRFLP and mtMSI are damage by free radicals and error repair by the polymerase gamma, the first mechanism being a major cause of MnlI mutations and a secondary cause of mtMSI.

DNA copy number changes in malignant ovarian germ cell tumors

Malignant ovarian germ cell tumors (OGCTs) include immature teratomas (ITs), dysgerminomas (DGs), endodermal sinus tumors (ESTs), choriocarcinomas, and embryonal carcinomas. Knowledge about the genetic changes associated with malignant OGCT development is sparse. We therefore analyzed 25 OGCTs (12 DGs, 4 ESTs, and 9 ITs) for gains and losses by comparative genomic hybridization. In total, more gains than losses were observed, and the number of alterations ranged from 0-20 per tumor. The average number of changes among DGs, ESTs, and ITs was 10, 6, and 1.4, respectively. The most common changes in DGs were gains from chromosome arms 1p (33%), 6p (33%), 12p (67%), 12q (75%), 15q (42%), 20q (50%), 21q (67%), and 22q (58%); gains of the whole of chromosomes 7 (42%), 8 (42%), 17 (42%), and 19 (50%); and losses from 13q (58%). Two of three DGs with a gonadoblastoma component showed gains of 3p21 and loss of 5p, whereas none of the nine pure DGs had these changes, suggesting that they might be characteristic either of gonadoblastoma or of DG developing from a gonadoblastoma. Gain of 12p and gain from 1q were seen in three of four ESTs, whereas gains from 3p, 11q, and Xp and loss from 18q were each found in two tumors. Five of the ITs revealed changes (range, 1-4 changes/tumor), with gains from 1p, 16p, 19, and 22q each being found in two tumors. We conclude that ovarian DGs and ESTs seem to develop via the same genetic pathways that are already known for testicular germ cell tumors. On the other hand, ITs do not exhibit gain of 12p and also typically show fewer changes than other malignant OGCTs, indicating that they arise via different pathogenetic mechanisms.

Genetic and epigenetic modification of MLH1 accounts for a major share of microsatellite-unstable colorectal cancers

Microsatellite instability (MSI) is a hallmark of hereditary nonpolyposis colorectal cancer, and in these patients, results from inherited defects in DNA mismatch repair genes, mostly MSH2 and MLH1. MSI also occurs in 15% of sporadic colorectal cancers, but in these tumors, its basis is less well characterized. We investigated 46 sporadic MSI+ colorectal cancers for changes in MSH2 and MLH1 protein expression, followed by the analysis of somatic mutation, loss of heterozygosity (LOH), and promoter hypermethylation as possible underlying defects. Most cases (36/46, 78%) showed lost or reduced MLH1 expression. Among these, a majority (83%) was associated with MLH1 promoter hypermethylation, whereas the rates of LOH and somatic mutation of MLH1 were 24% and 13%, respectively. Hypermethylation and LOH were inversely correlated, suggesting that they had alternative functions in the inactivation of MLH1. MSH2 expression was lost in 7/46 (15%), and of these, 2 (29%) showed LOH and/or somatic mutation of MSH2. We conclude that most sporadic MSI+ colorectal cancers have an MLH1-associated etiology and that epigenetic modification is a major mechanism of MLH1 inactivation. Moreover, we found a significantly lower prevalence for MLH1 promoter hypermethylation in hereditary nonpolyposis colorectal cancer tumors with MLH1 germline mutations (12/26, 46%), which might explain some differences that are known to occur in the clinicopathological characteristics and tumorigenic pathways between sporadic and hereditary MSI+ colorectal cancers.

Controlled 15-year trial on screening for colorectal cancer in families with hereditary nonpolyposis colorectal cancer

BACKGROUND & AIMS

Identification of the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome enables prevention of colorectal cancer (CRC) by means of colonoscopy and polypectomies. We evaluated the efficacy of screening in a controlled trial over 15 years.

METHODS

Incidence of CRC and survival were compared in 2 cohorts of at-risk members of 22 families with HNPCC. Colonic screening at 3-year intervals was arranged for 133 subjects; 119 control subjects had no screening. Genetic testing was offered to subjects in whose families the causative mutation was known.

RESULTS

CRC developed in 8 screened subjects (6%) compared with 19 control subjects (16 %; P = 0.014). The CRC rate was reduced by 62%. In mutation-positive subjects alone, the CRC rates were 18% in screened subjects and 41% in controls (P = 0.02). The decrease resulted from the removal of adenomas in 13 mutation-positive individuals (30%) and in 6 subjects with unknown mutation status (40%). All CRCs in the study group were local, causing no deaths, compared with 9 deaths caused by CRC in the controls. The overall death rates were 10 vs. 26 subjects in the study and control groups (P = 0.003), 4 vs. 12 in mutation-positive subjects (P = 0.05).

CONCLUSIONS

Colonoscopic screening at 3-year intervals more than halves the risk of CRC, prevents CRC deaths, and decreases overall mortality by about 65% in HNPCC families.

Genomic instability and target gene mutations in colon cancers with different degrees of allelic shifts

Two grades (high and low) of microsatellite instability (MSI) are known, depending on the number of mutated markers and the amount of allelic shifts. Forty-two colorectal tumors, previously found to have high-degree MSI at dinucleotidic repeat loci, were revisited with BAT26, a mononucleotide marker, and the number of shifted bases were counted. Seven tumors, all with local stages at diagnosis, had < or =6-bp deletions and consistently displayed shorter shifts also with other intronic mononucleotide markers. Analysis of mononucleotide tracts in the coding regions of MSH3, MSH6, BAX, and TGFbetaRII in the groups with large (>6 bp) and short (< or =6 bp) allelic shifts showed specific patterns of involvement for the individual genes: TGFbetaRII displayed a uniformly high rate of mutations, while MSH3, MSH6, and BAX were less frequently altered in tumors with short shifts. Our findings suggest that microsatellite instability arises gradually, evenly involving loci with similar features of length and repetition. However, target genes have a specific timing of mutation in this process: TGFbetaRII is involved in the early phases, while BAX and MSH6 are frequently associated with big size shifts and tumors with more advanced stages.

Hereditary nonpolyposis colorectal cancer (Lynch syndrome II) in Uruguay

PURPOSE

We updated an Uruguayan family with hereditary nonpolyposis colorectal cancer first described in 1977, incorporating knowledge of how the hMLH1 germline mutation has been established and shown to segregate in accord with the expected autosomal dominant mode of genetic transmission.

METHODS

DNA-based molecular genetic testing was performed in conjunction with genetic counseling. Individuals were provided with their genetic test results, so that at-risk family members would be able to benefit from targeted management programs.

RESULTS

We counseled 19 members of this kindred, 13 of whom were positive for the hMLH1 germline mutation. Specific recommendations for surveillance and management were provided. We were able to describe follow-up, including anecdotal cancer survival and pathology findings extending from the initial 1977 report of this family to the present. A remarkable sibship within this kindred was comprised of eight siblings, six of whom underwent resections for colorectal carcinoma between 1963 and 1971. Colon carcinomas before 1977 in this sibship were treated with classic hemicolectomies. Of those who had hemicolectomies for their first primary colorectal cancers, two had a second colon cancer primary, and two had a third colon cancer primary.

CONCLUSIONS

Attention given to this extended family with hereditary nonpolyposis colorectal cancer has had a positive impact on the physician community in Uruguay, leading to the identification of additional families with hereditary nonpolyposis colorectal cancer.

Evaluation of a counselling protocol for predictive genetic testing for hereditary non-polyposis colorectal cancer

OBJECTIVES

To evaluate the feasibility of a reduced counselling programme for predictive genetic testing for hereditary non-polyposis colorectal cancer (HNPCC) in terms of counsellees' opinions on the extent and significance of genetic counselling and need for psychological support at different phases of the testing procedure.

DESIGN

Prospective follow up study with pre-test questionnaire assessment of background sociodemographic variables. The protocol comprised a pre-test counselling session, a period for reflection, and a test disclosure session. The outcome variables were studied by post-test questionnaires at one month and one year follow up.

SUBJECTS

Two hundred and seventy one high risk members of 36 families with HNPCC who attended both counselling sessions and completed the questionnaires.

RESULTS

The pre-test counselling was considered fairly or very useful by 89% of respondents and one post-test session was considered sufficient by over 80% of respondents at follow up. Fifty three percent would have used extra psychological support had it been offered with the counselling. On enquiry one year after receiving the test result, only 2% stated that the need for support was at its greatest at that time, while the majority (46%) reported that the need for support had been greatest at the moment of test disclosure.

CONCLUSIONS

A protocol that includes one comprehensive pre-test counselling session and a test disclosure session, supplemented with the option of professional psychological support, seems to be sufficient for both the educational and supportive needs of counsellees. Only a minority expressed a need for post-test follow up sessions, which suggests that, in this disorder, resources can be directed to the beneficial surveillance programmes rather than to extensive psychological support.

Aberrant CpG-island methylation has non-random and tumour-type-specific patterns

CpG islands frequently contain gene promoters or exons and are usually unmethylated in normal cells. Methylation of CpG islands is associated with delayed replication, condensed chromatin and inhibition of transcription initiation. The investigation of aberrant CpG-island methylation in human cancer has primarily taken a candidate gene approach, and has focused on less than 15 of the estimated 45,000 CpG islands in the genome. Here we report a global analysis of the methylation status of 1,184 unselected CpG islands in each of 98 primary human tumours using restriction landmark genomic scanning (RLGS). We estimate that an average of 600 CpG islands (range of 0 to 4,500) of the 45,000 in the genome were aberrantly methylated in the tumours, including early stage tumours. We identified patterns of CpG-island methylation that were shared within each tumour type, together with patterns and targets that displayed distinct tumour-type specificity. The expression of many of these genes was reactivated by experimental demethylation in cultured tumour cells. Thus, the methylation of particular subsets of CpG islands may have consequences for specific tumour types.

Predictive genetic testing for hereditary non-polyposis colorectal cancer: uptake and long-term satisfaction

The aim of this prospective study was to assess the uptake of predictive genetic testing for hereditary non-polyposis colorectal cancer (HNPCC) and its associations with sociodemographic and other factors, and long-term satisfaction with taking the test. The test was offered to all high-risk members (n = 446) of 36 Finnish HNPCC families in which the mutation was known. The procedure comprised an educational counselling session, a period for reflection, and a test disclosure session. Data were collected by questionnaires sent before the educational counselling and 1 month and 1 year after the test disclosure. Of those eligible, 85% (n = 381) completed the first questionnaire study. Non-participation was more common among men living alone who had not participated in the clinical cancer surveillance programme. Of the 347 subjects who attended counselling, 334 (75% of all subjects) were actually tested. After logistic-regression analysis, the only significant factor predicting test acceptance proved to be employment status: those employed were more likely than others to accept the test (odds ratio = 2.25; 95% confidence intervals, 1.09 to 4.6 1). At follow-up, over 90% of the subjects were fully satisfied with the decision to take the test. In conclusion, acceptance of the test was considerably higher than in previously reported studies. We attribute this to our careful face-to-face individualized counselling, our health care system, and to attitudes of the Finnish population, which are generally favourable towards health care and disease prevention.

Missense and nonsense mutations in codon 659 of MLH1 cause aberrant splicing of messenger RNA in HNPCC kindreds

Germline mutations that give rise to premature termination codons in mRNAs have frequently been associated with aberrant processing of the nascent transcripts. This can take the form either of nonsense-mediated mRNA decay or of aberrant splicing of the pre-mRNA. In a family affected by hereditary nonpolyposis colorectal cancer, a two-nucleotide deletion in codon 659, which introduces a frameshift and a new stop codon in exon 17 of the DNA mismatch repair gene MLH1, has been reported to lead to skipping of the exon. We now report that this phenomenon occurs also when there are missense or nonsense mutations in this codon. Our results thus suggest that in aberrant splicing the nature of the mutation may be less important than its position within the exon. These findings are of importance to mutation interpretation, as they imply that aberrant splicing could be associated even with silent mutations that do not lead to amino acid substitutions. Genes Chromosomes Cancer 26:372-375, 1999.

Epigenetic phenotypes distinguish microsatellite-stable and -unstable colorectal cancers

Aberrant DNA methylation is a common phenomenon in human cancer, but its patterns, causes, and consequences are poorly defined. Promoter methylation of the DNA mismatch repair gene MutL homologue (MLH1) has been implicated in the subset of colorectal cancers that shows microsatellite instability (MSI). The present analysis of four MspI/HpaII sites at the MLH1 promoter region in a series of 89 sporadic colorectal cancers revealed two main methylation patterns that closely correlated with the MSI status of the tumors. These sites were hypermethylated in tumor tissue relative to normal mucosa in most MSI(+) cases (31/51, 61%). By contrast, in the majority of MSI(-) cases (20/38, 53%) the same sites showed methylation in normal mucosa and hypomethylation in tumor tissue. Hypermethylation displayed a direct correlation with increasing age and proximal location in the bowel and was accompanied by immunohistochemically documented loss of MLH1 protein both in tumors and in normal tissue. Similar patterns of methylation were observed in the promoter region of the calcitonin gene that does not have a known functional role in tumorigenesis. We propose a model of carcinogenesis where different epigenetic phenotypes distinguish the colonic mucosa in individuals who develop MSI(+) and MSI(-) tumors. These phenotypes may underlie the different developmental pathways that are known to occur in these tumors.

A new tool for the rapid cloning of amplified and hypermethylated human DNA sequences from restriction landmark genome scanning gels

Restriction landmark genome scanning (RLGS) is an effective genome-scanning technique capable of identifying DNA amplification and aberrant DNA methylation. Previously published methods for the cloning of human DNA fragments from RLGS gels have been successful only for high-copy-number fragments (repetitive elements or DNA amplifications). We present here the first technique capable of efficiently cloning single-copy human DNA fragments ("spots") identified in RLGS profiles. This technique takes advantage of a plasmid-based, human genomic DNA, NotI/EcoRV boundary library. The library is arrayed in microtiter plates. When clones from a single plate are pooled and mixed with genomic DNA, the resultant RLGS gel is a normal profile with a defined set of spots showing enhanced intensity for that particular plate. This was performed for a set of 32 plates as well as their pooled rows and columns. Thus, we have mapped individual RLGS spots to exact plate, row, and column addresses in the library and have thereby obtained immediate access to these clones. The feasibility of the technique is demonstrated in examples of cloning methylated DNA fragments identified in human breast tumor and testicular tumor RLGS profiles and in the cloning of an amplified DNA fragment identified in a human medulloblastoma RLGS profile.

Cancer risk in mutation carriers of DNA-mismatch-repair genes

Excessive incidence of various cancers is a challenging feature of the hereditary-non-polyposis-colorectal-cancer (HNPCC) syndrome. This study estimated the cancer incidences in HNPCC compared with the general population. Individuals in a cohort of 1763 members of 50 genetically diagnosed families were categorized according to their genetic status as mutation carriers, non-carriers, or individuals at 50 or 25% risk of being a carrier. Incidences of cancers in these groups were compared with those in the Finnish population overall. In 360 mutation carriers, standardized incidence ratios (SIR) were significantly increased for colorectal [68; 95% confidence intervals (CI), 56 to 81], endometrial (62; 95% CI, 44 to 86), ovarian (13; 95% CI, 5.3 to 25), gastric (6.9; 95% CI, 3.6 to 12), biliary tract (9.1; 95% CI, 1.1 to 33), uro-epithelial (7.6; 95% CI, 2.5 to 18) and kidney (4.7; 95% CI, 1 to 14) cancers and for central-nervous-system tumours (4.5; 95% CI, 1.2 to 12). The SIR increased with increasing likelihood of being a mutation carrier. The cumulative cancer incidences were 82, 60, 13 and 12% for colorectal, endometrial, gastric and ovarian cancers respectively. For other tumours associated with increased risk, corresponding incidences were below 4%. Interestingly, the incidence of endometrial cancer (60%) exceeded that for colorectal cancer in women (54%). The tumour spectrum associated with germline mutations of DNA-mismatch-repair genes involves 8 or more organ sites, suggesting a need to develop methods to screen for extra-colonic cancer also.

Cancer risk in mutation carriers of DNA-mismatch-repair genes

Excessive incidence of various cancers is a challenging feature of the hereditary-non-polyposis-colorectal-cancer (HNPCC) syndrome. This study estimated the cancer incidences in HNPCC compared with the general population. Individuals in a cohort of 1763 members of 50 genetically diagnosed families were categorized according to their genetic status as mutation carriers, non-carriers, or individuals at 50 or 25% risk of being a carrier. Incidences of cancers in these groups were compared with those in the Finnish population overall. In 360 mutation carriers, standardized incidence ratios (SIR) were significantly increased for colorectal [68; 95% confidence intervals (CI), 56 to 81], endometrial (62; 95% CI, 44 to 86), ovarian (13; 95% CI, 5.3 to 25), gastric (6.9; 95% CI, 3.6 to 12), biliary tract (9.1; 95% CI, 1.1 to 33), uro-epithelial (7.6; 95% CI, 2.5 to 18) and kidney (4.7; 95% CI, 1 to 14) cancers and for central-nervous-system tumours (4.5; 95% CI, 1.2 to 12). The SIR increased with increasing likelihood of being a mutation carrier. The cumulative cancer incidences were 82, 60, 13 and 12% for colorectal, endometrial, gastric and ovarian cancers respectively. For other tumours associated with increased risk, corresponding incidences were below 4%. Interestingly, the incidence of endometrial cancer (60%) exceeded that for colorectal cancer in women (54%). The tumour spectrum associated with germline mutations of DNA-mismatch-repair genes involves 8 or more organ sites, suggesting a need to develop methods to screen for extra-colonic cancer also.

Genetic polymorphisms in carcinogen metabolism and their association to hereditary nonpolyposis colon cancer

BACKGROUND & AIMS

The phenotype of hereditary nonpolyposis colorectal cancer shows interfamilial and intrafamilial variation even in the presence of identical predisposing mutations, suggesting the existence of additional phenotype determinants. The modifying role of genetic polymorphisms in loci involved in carcinogen metabolism was studied.

METHODS

We focused on colon cancers from kindreds sharing one of two predisposing mutations (mutation 1 or 2) in the mismatch repair gene MLH1 (78 and 14 tumors, respectively). Polymorphisms in N-acetyltransferase 1 (NAT1) and glutathione S-transferase (GST) M1 and GSTT1 were investigated.

RESULTS

The NAT1 allele 10 was associated with lower median age at diagnosis in both groups. In mutation 1 group, the NAT1 allele 10 was a risk factor for distal tumor location, both alone (P = 0.028) and combined with the GSTT1-positive genotype (P = 0.008). On the other hand, the combined null genotype of GSTM1 and GSTT1 was associated with proximal tumors. Associations with tumor location were not observed in patients with mutation 2, probably reflecting a small sample size.

CONCLUSIONS

The results suggest that genetic polymorphisms in carcinogen metabolism modify the age of onset and tumor location in individuals with inherited deficiency of DNA mismatch repair.

Mismatch repair genes and mononucleotide tracts as mutation targets in colorectal tumors with different degrees of microsatellite instability

Microsatellite instability occurs in 15% of colorectal carcinomas and may be due to replication errors (RER). The pattern of instability--'severe' vs 'mild'--and the tumorigenic pathway, as reflected by the involvement of functionally important genes, may vary according to the underlying gene(s). We defined 'mild' RER as mono- or tetranucleotide repeat instability in the absence of widespread instability at dinucleotide repeats and studied 15 colorectal tumors with this phenotype for mutations in the DNA mismatch repair genes MSH2, MLH1, MSH3, and MSH6. No mutations were found, suggesting that these genes were not implicated. We then compared colorectal cancers with 'mild' RER (n = 15), and those with 'severe' RER without (n = 11) or with (n = 22) detectable mutations in MSH2 or MLH1 to assess the involvement of mononucleotide repeats contained in the coding regions of MSH3, MSH6, BAX, and TGFbeta RII. The combined mutation rates of the above mentioned loci varied significantly between the three groups of tumors, being 0%, 25% and 52%, respectively. Furthermore, the individual genes showed specific patterns of involvement; for example, among tumors with 'severe' RER, TGFbeta RII displayed uniformly high mutation rates while MSH3, MSH6, and BAX were more frequently altered in tumors that also showed MSH2 or MLH1 mutations. Our findings suggest that different subcategories exist among unstable tumors, defined by the RER pattern on the one hand and tumorigenic pathway on the other, and structural changes of MSH2 and MLH1 are likely to explain only a proportion of these cases.

The genetics of hereditary common cancers

Subsets of patients with common cancers belong to families in which the predisposition is inherited in a regular Mendelian fashion. Genes underlying these cancers are now recognized in colorectal cancer (APC, mismatch repair genes, LKB1) and in breast cancer (BRCA1, BRCA2) whereas, in prostate cancer, a locus in chromosome 1 (HPC1) has been proposed on the basis of linkage analysis. Major challenges are to determine the population incidence of these mutations, their penetrance, phenotypic expression, and the effects of modifier genes and epigenetic factors. Finally, the role of encoded proteins in carcinogenesis is a matter of major interest.

Incidence of hereditary nonpolyposis colorectal cancer and the feasibility of molecular screening for the disease

BACKGROUND

Genetic disorders that predispose people to colorectal cancer include the polyposis syndromes and hereditary nonpolyposis colorectal cancer. In contrast to the polyposis syndromes, hereditary nonpolyposis colorectal cancer lacks distinctive clinical features. However, a germ-line mutation of DNA mismatch-repair genes is a characteristic molecular feature of the disease. Since clinical screening of carriers of such mutations can help prevent cancer, it is important to devise strategies applicable to molecular screening for this disease.

METHODS

We prospectively screened tumor specimens obtained from 509 consecutive patients with colorectal adenocarcinomas for DNA replication errors, which are characteristic of hereditary colorectal cancers. These replication errors were detected through microsatellite-marker analyses of tumor DNA. DNA from normal tissue from the patients with replication errors was screened for germ-line mutations of the mismatch-repair genes MLH1 and MSH2.

RESULTS

Among the 509 patients, 63 (12 percent) had replication errors. Specimens of normal tissue from 10 of these 63 patients had a germ-line mutation of MLH1 or MSH2. Of these 10 patients (2 percent of the 509 patients), 9 had a first-degree relative with endometrial or colorectal cancer, 7 were under 50 years of age, and 4 had had colorectal or endometrial cancer previously.

CONCLUSIONS

In this series of patients with colorectal cancer in Finland, at least 2 percent had hereditary nonpolyposis colorectal cancer. We recommend testing for replication errors in all patients with colorectal cancer who meet one or more of the following criteria: a family history of colorectal or endometrial cancer, an age of less than 50 years, and a history of multiple colorectal or endometrial cancers. Patients found to have replication errors should undergo further analysis for germ-line mutations in DNA mismatch-repair genes.

[Goodness in nurse's heart matters. What is goodness in nursing practice?]

Manifestation of goodness in nursing has been researched very little contrary to good care. This article is based on a Master's thesis the aim of which is to describe goodness in nursing as it is experienced by a nurse. The research is qualitative and based on the phenomenological philosophy of science in which the truth is understood through an individual experience. The research method is developed by Paterson and Zderad. There were 15 nurses who participated in the research and the following results were derived from their essays. Life experience and prevailing values of society influence on the nurse's values which are reflected in nursing practice. The nurse's sensitivity, maturity, flexibility, hardiness and ability to grow combined with technical skills facilitate goodness. Goodness is an open relationship with another people. In this constantly living relationship closeness, listening by heart and willingness to bring good to the other people exist simultaneously.

Mutations predisposing to hereditary nonpolyposis colorectal cancer: database and results of a collaborative study. The International Collaborative Group on Hereditary Nonpolyposis Colorectal Cancer

BACKGROUND & AIMS

Germline mutations in four DNA mismatch repair genes are known to cause susceptibility to hereditary nonpolyposis colorectal cancer (HNPCC). The rapidly increasing information about these mutations needs to be collected and appropriately stored to facilitate further studies on the biological and clinical significance of the findings.

METHODS

The International Collaborative Group on HNPCC has established a database of DNA mismatch repair gene mutations and polymorphisms. In this report, 126 predisposing mutations were analyzed.

RESULTS

A majority of the mutations affected either the Mut L homologue (MLH) 1 (n = 75) or the Mut S homologue (MSH) 2 (n = 48) and were quite evenly distributed, with some clustering in MSH2 exon 12 and MLH1 exon 16. Most MSH2 mutations consisted of frameshift (60%) or nonsense changes (23%), whereas MLH1 was mainly affected by frameshift (40%) or missense alterations (31%). Although most mutations were unique, a few common recurring mutations were identified. Of the families studied (n = 202), 82% met the Amsterdam criteria and 15% did not; the general mutation profile was similar in both groups.

CONCLUSIONS

The construction of mutation profiles will facilitate the development of diagnostic strategies in HNPCC.

MSH2 and MLH1 mutations in sporadic replication error-positive colorectal carcinoma as assessed by two-dimensional DNA electrophoresis

Replication errors (RER) are frequently seen in both sporadic and hereditary forms of colorectal cancer. In hereditary nonpolyposis colorectal cancer (HNPCC), RER is associated with defects in DNA mismatch repair genes. Two of these genes, MSH2 and MLH1, account for a major share of this cancer syndrome. In order to assess the role of these genes in sporadic RER+ colorectal carcinoma, we have carried out a mutation analysis of MSH2 and MLH1 by two-dimensional (2-D) DNA electrophoresis, including heteroduplexing and separation in a denaturing gradient. All exons were amplified using multiplex PCR and were separated on the basis of both size and base pair composition under a single set of experimental conditions. Exons showing a spot position different from normal were sequenced. In screening 33 unselected, sporadic RER+ colorectal tumors, a germline mutation accompanied by loss of heterozygosity in tumor tissue was found in two patients. They were among the 4 patients out of the 33 screened that were diagnosed before the age of 50 years. In 8 of the remaining 31 tumors (26%), presence of somatic mutations (9 in total) could be demonstrated. While suggesting involvement of other genes in a substantial part of sporadic RER+ colorectal carcinomas, our results also demonstrate a clear role of MSH2 and MLH1 in these sporadic tumors and show that young sporadic RER+ colorectal carcinoma patients have a high probability of germline mutations. This has important implications for genetic testing and management of young colorectal cancer patients and their families.

DNA mismatch repair gene mutations in human cancer

A new pathogenetic mechanism leading to cancer has been delineated in the past 3 years when human homologues of DNA mismatch repair (MMR) genes have been identified and shown to be involved in various types of cancer. Germline mutations of MMR genes cause susceptibility to a hereditary form of colon cancer, hereditary nonpolyposis colon cancer (HNPCC), which represents one of the most common syndromes associated with cancer predisposition in man. Tumors from HNPCC patients are hypermutable and show length variation at short tandem repeat sequences, a phenomenon referred to as microsatellite instability or replication errors. A similar abnormality is found in a proportion of sporadic tumors of the colorectum as well as a variety of other organs; acquired mutations in MMR genes or other endogenous or exogenous causes may underlie these cases. Genetic and biochemical characterization of the functions of normal and mutated MMR genes elucidates mechanisms of cancer development and provides tools for diagnostic applications.

Microsatellite instability in cervical and endometrial carcinomas

Microsatellite instability has been found preferentially in tumours associated with the hereditary non-polyposis-colorectal-cancer (HNPCC) syndrome. This phenotype, manifested as new alleles at microsatellite loci, and often the result of a defective mismatch-repair gene, is seen as allelic mobility shifts during electrophoretic runs. We examined possible alterations at 8 dinucleotide loci mapping to 6 different chromosomes in endometrial cancers (n = 20) and cervical cancers (n = 82). Overall instability was found in 30% of the endometrial cancers and in 6% of the cervical cancers, including 3 (15%) and 2 (2%) tumours, respectively, unstable at more than one locus. In contrast to the endometrial cancer sub-group, the affected cervical cancers were characterized by one or two new alleles at one or few loci. By DNA ploidy measurements 5 diploid endometrial cancers were microsatellite-unstable vs. one diploid of 6 unaltered cases (p = 0.015; Fisher's exact test). Our data confirm that a sub-set of diploid sporadic endometrial cancers are characterized by a mutator phenotype similar to that found in colorectal cancer. In contrast, among cervical cancers, not characterized by the HNPCC-tumour spectrum, this mutator phenotype is seen infrequently, and positive cases appear to display only minor alterations.

Mutations predisposing to hereditary nonpolyposis colorectal cancer

Since 1993 four genes have been identified that, when mutated, confer predisposition to a form of hereditary colon cancer (hereditary nonpolyposis colorectal cancer [HNPCC]). These genes belong to the Mut-related family of DNA mismatch repair genes whose protein products are responsible for the recognition and correction of errors that arise during DNA replication. Mutational inactivation of both copies of a DNA mismatch repair gene results in a profound repair defect demonstrable by biochemical assays, and in vivo this defect is presumed to lead to progressive accumulation of secondary mutations throughout the genome, some of which affect important growth-regulatory genes and, hence, give rise to cancer. To date, more than 70 different germline mutations have been detected in DNA mismatch repair genes and shown to be associated with HNPCC. Current evidence suggests that two genes, MSH2 and MLH1, account for roughly equal proportions of HNPCC kindreds, together being responsible for a majority of these families, but striking interethnic differences occur. Most mutations lead to truncated protein products. Mutation screening is quite demanding in HNPCC since, with a few exceptions, the predisposing mutations typically vary from kindred to kindred and individual mutations are scattered throughout the genes. Knowledge of the predisposing mutations allows genotype-phenotype correlations and forms the basis for further studies clarifying the pathogenesis of this disorder. In at-risk individuals, it allows predictive testing for cancer susceptibility and, consequently, appropriate clinical management of mutation carriers and noncarriers.