Close linkage to chromosome 3p and conservation of ancestral founding haplotype in hereditary nonpolyposis colorectal cancer families

Founder variants and population genomes-Toward precision medicine

Human migration and community specific cultural practices have contributed to founder events and enrichment of the variants associated with genetic diseases. While many founder events in isolated populations have remained uncharacterized, the application of genomics in clinical settings as well as for population scale studies in the recent years have provided an unprecedented push towards identification of founder variants associated with human health and disease. The discovery and characterization of founder variants could have far reaching implications not only in understanding the history or genealogy of the disease, but also in implementing evidence based policies and genetic testing frameworks. This further enables precise diagnosis and prevention in an attempt towards precision medicine. This review provides an overview of founder variants along with methods and resources cataloging them. We have also discussed the public health implications and examples of prevalent disease associated founder variants in specific populations.

Molecular Genetics of Hereditary Non-Polyposis Colorectal Cancer (HNPCC)

The story of the molecular genetics of HNPCC is one of astonishingly rapid achievements. In just 16 months, from May 1993 to September 1994, four different genes, namely hMSH2, hMLH1, hPMS1 and hPMS2 have been identified and demonstrated to be associated with the disease. Their cloning was facilitated by the finding that tumor cells in HNPCC patients display a hypermutability of DNA short tandem repeats (microsatellite instability). In fact, HNPCC associated genes are the human counterparts of genetic elements known to control the fidelity of DNA replication in lower organisms. So far, more than 50 germline mutations of hMSH2 and hMLH1 genes have been reported in HNPCC kindreds. In addition, somatic mutations have been documented in hereditary as well as sporadic cancers. Unfortunately, the molecular diagnosis of HNPCC is hampered by the lack of mutational “hot spots” and of clearly defined genotype-phenotype correlations and different screening methods are to be employed for the analysis of affected and at-risk individuals.

Commonalities in Development of Pure Breeds and Population Isolates Revealed in the Genome of the Sardinian Fonni's Dog

The island inhabitants of Sardinia have long been a focus for studies of complex human traits due to their unique ancestral background and population isolation reflecting geographic and cultural restriction. Population isolates share decreased genomic diversity, increased linkage disequilibrium, and increased inbreeding coefficients. In many regions, dogs and humans have been exposed to the same natural and artificial forces of environment, growth, and migration. Distinct dog breeds have arisen through human-driven selection of characteristics to meet an ideal standard of appearance and function. The Fonni's Dog, an endemic dog population on Sardinia, has not been subjected to an intensive system of artificial selection, but rather has developed alongside the human population of Sardinia, influenced by geographic isolation and unregulated selection based on its environmental adaptation and aptitude for owner-desired behaviors. Through analysis of 28 dog breeds, represented with whole-genome sequences from 13 dogs and ∼170,000 genome-wide single nucleotide variants from 155 dogs, we have produced a genomic illustration of the Fonni's Dog. Genomic patterns confirm within-breed similarity, while population and demographic analyses provide spatial identity of Fonni's Dog to other Mediterranean breeds. Investigation of admixture and fixation indices reveals insights into the involvement of Fonni's Dogs in breed development throughout the Mediterranean. We describe how characteristics of population isolates are reflected in dog breeds that have undergone artificial selection, and are mirrored in the Fonni's Dog through traditional isolating factors that affect human populations. Lastly, we show that the genetic history of Fonni's Dog parallels demographic events in local human populations.

Long range linkage disequilibrium across the human genome

Long-range linkage disequilibria (LRLD) between sites that are widely separated on chromosomes may suggest that population admixture, epistatic selection, or other evolutionary forces are at work. We quantified patterns of LRLD on a chromosome-wide level in the YRI population of the HapMap dataset of single nucleotide polymorphisms (SNPs). We calculated the disequilibrium between all pairs of SNPs on each chromosome (a total of >2×10(11) values) and evaluated significance of overall disequilibrium using randomization. The results show an excess of associations between pairs of distant sites (separated by >0.25 cM) on all of the 22 autosomes. We discuss possible explanations for this observation.

Microsatellite instability--MSI markers (BAT26, BAT25, D2S123, D5S346, D17S250) in rectal cancer

BACKGROUND

Colorectal cancer has an important genetic component. Microsatellites are considered phenotypic markers of prognosis, therapeutic response and identify patients with mutations in DNA repair genes.

AIM

To evaluate the molecular profile of tumors underwent to transanal endoscopic microsurgery-TEM in surgical treatment of rectal cancer.

METHOD

Thirty eight surgical specimens were evaluated according to pathological staging and the region of the tumor were dissected and submitted to DNA extraction. The colorectal tumors were tested for microsatellite instability-MSI using a panel of five markers (BAT25, BAT26, D2S123, D5S346, and D17S2720) technique of Polymerase Chain Reaction (PCR).

RESULT

From total 63% were male and 47% female, with mean age of 58.4 years. In relation to tumor type adenomas were 58%, 24% low-grade adenomas and 76% high grade; 42% were carcinomas. The depth of resection 80% included the rectal perirenal fat and 20% the muscularis propria. The most frequent microsatellite amplification was BAT26 (100%) and lowest D17S2720 (85.4%). Sixteen patients (42%) were MSI, ten were carcinomas, two low grade adenomas and four high grade. Twenty-two cases (68%) showed microsatellite stable-MSS. The allelic loss of microsatellite markers was statistically significant in cases of carcinoma in relation to adenomas. The most frequent microsatellite amplification was BAT26 (100%) and lower D17S2720 (85.4%), 16 patients (42%) had microsatellite instability-MSI thereof ten were carcinomas, two low grade adenomas, four high-grade adenomas and 22 cases (58%) were microsatellite stable-MSS.

CONCLUSION

Microsatellite instability (MSI-H) was significantly associated with rectal carcinomas, confirming its use as a prognostic marker in colorectal carcinogenesis.

DNA repair in human pluripotent stem cells is distinct from that in non-pluripotent human cells

The potential for human disease treatment using human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells (iPSCs), also carries the risk of added genomic instability. Genomic instability is most often linked to DNA repair deficiencies, which indicates that screening/characterization of possible repair deficiencies in pluripotent human stem cells should be a necessary step prior to their clinical and research use. In this study, a comparison of DNA repair pathways in pluripotent cells, as compared to those in non-pluripotent cells, demonstrated that DNA repair capacities of pluripotent cell lines were more heterogeneous than those of differentiated lines examined and were generally greater. Although pluripotent cells had high DNA repair capacities for nucleotide excision repair, we show that ultraviolet radiation at low fluxes induced an apoptotic response in these cells, while differentiated cells lacked response to this stimulus, and note that pluripotent cells had a similar apoptotic response to alkylating agent damage. This sensitivity of pluripotent cells to damage is notable since viable pluripotent cells exhibit less ultraviolet light-induced DNA damage than do differentiated cells that receive the same flux. In addition, the importance of screening pluripotent cells for DNA repair defects was highlighted by an iPSC line that demonstrated a normal spectral karyotype, but showed both microsatellite instability and reduced DNA repair capacities in three out of four DNA repair pathways examined. Together, these results demonstrate a need to evaluate DNA repair capacities in pluripotent cell lines, in order to characterize their genomic stability, prior to their pre-clinical and clinical use.

RACIAL DIFFERENCES IN MLH1 AND MSH2 MUTATION: AN ANALYSIS OF YELLOW RACE AND WHITE RACE BASED ON THE INSIGHT DATABASE

MLH1 and MSH2 mutations underlie 90% of hereditary nonpolyposis colorectal cancer (HNPCC) mutations. The International Society of Gastrointestinal Hereditary Tumors (InSiGHT) has established an international database of mutations associated with HNPCC. Based on the InSiGHT database and the original references that reported the mutations, we analyzed the distributions of MLH1 and MSH2 mutations in yellow race and white race respectively and compared them subsequently. We found: (1) the distributions of mutation individuals in exon 1, 17 and 19 of MLH1 gene and in exon 2 of MSH2 gene showed significant differences between the two race groups (p < 0.05); (2) the distributions of mutation types in exon 2, 7 and 18 of MLH1 and exon 10 and 16 of MSH2 showed significant differences (p < 0.05); and (3) three mutations (c.649C > T, c.1625A > T and c.1721T > C) in MLH1 and five mutations (c.23C > T, c.187dupG, c.505A > G, c.1168C > T and c.2211-6T > C) in MSH2 have much higher frequency in yellow race than those in white race. Furthermore, three mutations (c.1453G > C, c.1742C > T and c.1758dupC) in MLH1 and two mutations (c.1255C > A and c.1886A > G) in MSH2 were only found in yellow race, which implies that specific mutations in yellow race need more attention when screening mutations in these two genes.

Microsatellite instability in colorectal cancer: from molecular oncogenic mechanisms to clinical implications

BACKGROUND

Microsatellite instability (MSI) constitutes an important oncogenic molecular pathway in colorectal cancer (CRC), representing approximately 15% of all colorectal malignant tumours. In roughly one third of the cases, the underlying DNA mismatch repair (MMR) defect is inherited through the transmission of a mutation in one of the genes involved in MMR, predominantly MSH2 and MLH1, or less frequently, MSH6 or PMS2. In the overwhelming number of sporadic cases, MSI results from epigenetic MLH1 silencing through hypermethylation of its promoter. MMR deficiency promotes colorectal oncogenesis through the accumulation of numerous mutations in crucial target genes harbouring mononucleotide repeats, notably in those involved in the control of cell proliferation and differentiation, as well as DNA damage signalling and repair.

DESIGN

In this review, we describe the molecular aspects of the MMR system and the biological consequences of its defect on the oncogenic process, and we discuss the various experimental systems used to evaluate the efficacy of cytotoxic drugs on MSI colorectal cells lines. There is increasing evidence showing that MSI CRCs differ from all CRCs in terms of prognosis and response to the treatment. We report the clinical studies that have evaluated the prognostic and predictive value of MSI status on clinical outcome in patients treated with various chemotherapy regimens used in the adjuvant setting or for advanced CRCs.

CONCLUSION

In view of this, the opportunity of a systematic MSI phenotyping in the clinical management of patients with CRC is further discussed.

A MLH1 polymorphism that increases cancer risk is associated with better outcome in sporadic colorectal cancer

Germline mutations or the malfunctioning of postreplicative mismatch repair genes (MMR) are responsible of hereditary nonpolyposis colorectal cancer (HNPCC), and are also implied in some sporadic colorectal cancer (CRC) forms without any familial history of this disease. Besides germinal mutations and methylation, single-nucleotide polymorphisms (SNP) can predispose to nonfamilial CRC with low to moderate penetrance. In this case-control study, we analyzed three MLH1 single-nucleotide polymorphisms (exon 5: 415G-->C, rs28930073; exon 8: 655A-->G, rs1799977 and exon 16: 1852-1853AA-->GC) in 140 sporadic colorectal cancer cases and 125 healthy individuals to evaluate the relationship among CRC risk and clinicopathologic and genetic characteristics of the tumors. In our study, no 415G-->C variant carrier was found among all analyzed samples. The 1852-1853AA-->GC is a rare variant detected in heterozygoses in five controls and one case. In relation to the more frequent 655A-->G polymorphism, association analyses revealed that G carriers (AG or GG genotype) displayed a higher risk of CRC compared with AA homozygous [odds ratio (OR) AG=2.55, 95% confidence interval (CI)=1.48-4.39; P=0.01 and OR GG=2.48, 95% CI=1.20-5.11; P=0.01, respectively]. G-carrier males showed high CRC risk compared with homozygous AA wild-type individuals (OR: AG=3.05; 95% CI=1.49-6.26, P=0.002; OR: GG=3.60; 95% CI=1.29-10.03). Nevertheless, patients carrying the G allele displayed a better outcome than wild-type genotype carriers (log rank=7.26; P=0.007) and did not present vascular invasion (P=0.03), distant metastasis (P=0.004), or recurrence (P=0.01). MLH1 655A-->G change is associated with an increased risk, although it seems to have a favorable effect on patients, providing a better outcome. Moreover, our results suggest that for genomic profiling to predict the clinical outcome of patients with colorectal cancer, gender must also be considered.

Germ line MLH1 and MSH2 mutations in Taiwanese Lynch syndrome families: characterization of a founder genomic mutation in the MLH1 gene

This multicenter study evaluated the mutation spectrum and frequencies of the MLH1 and MSH2 genes and determined the occurrence of large genomic deletions in 93 unrelated Taiwanese families that fulfilled the Amsterdam criteria II by denaturing high-performance liquid chromatography analysis, DNA sequencing for aberrant chromatograms, and multiplex ligation-dependent probe amplification analysis. In total, 38 pathogenic mutations (10 large deletions and 28 point mutations or small deletion/insertions) in the MSH2 or MLH1 gene were identified in 61 of the 93 families (66%). Three of the 10 large deletions and 14 of the 28 point mutations or small insertions/deletions have not been reported elsewhere. Three mutations in the MLH1 gene, the MLH1c.1846_1848delAAG (5 families), deletion exons 11-15 (4 unrelated families), and MLH1c.793C>T (13 unrelated families), accounted for 35% of all cases with pathogenic mutations. Haplotype analysis indicated that mutant c.793C>T alleles were derived from two distinct common founders that might be inherited from a single ancestor of presumably Chinese origin. As a mutation detection strategy for Taiwanese Lynch syndrome patients, we recommend that diagnosis starts with screening for large genomic deletions and continues by screening for common mutations in exons 10 and 16 of the MLH1 gene prior to searching for small mutations in the remaining exons.

Hereditary ovarian carcinoma: heterogeneity, molecular genetics, pathology, and management

Hereditary ovarian cancer accounts for at least 5% of the estimated 22,000 new cases of this disease during 2009. During this same time, over 15,000 will die from malignancy ascribed to ovarian origin. The bulk of these hereditary cases fits the hereditary breast-ovarian cancer syndrome, while virtually all of the remainder will be consonant with the Lynch syndrome, disorders which are autosomal dominantly inherited. Advances in molecular genetics have led to the identification of BRCA1 and BRCA2 gene mutations which predispose to the hereditary breast-ovarian cancer syndrome, and mutations in mismatch repair genes, the most common of which are MSH2 and MLH1, which predispose to Lynch syndrome. These discoveries enable relatively certain diagnosis, limited only by their variable penetrance, so that identification of mutation carriers through a comprehensive cancer family history might be possible. This paper reviews the subject of hereditary ovarian cancer, with particular attention to its molecular genetic basis, its pathology, and its phenotypic/genotypic heterogeneity.

Screening for BRCA1 and BRCA2 mutations in Eastern Finnish breast/ovarian cancer families

Familial aggregation is thought to account for 5-10% of all breast cancer cases, and high penetrance breast and ovarian cancer susceptibility genes BRCA1 and BRCA2 explain < or =20% of these. Hundreds of mutations among breast/ovarian cancer families have been found in these two genes. The mutation spectrum and prevalence, however, varies widely among populations. Thirty-six breast/ovarian cancer families were identified from a population sample of breast and ovarian cancer cases among a relatively isolated population in Eastern Finland, and the frequency of BRCA1/BRCA2 germline mutations were screened using heteroduplex analysis, protein truncation test and sequencing. Five different mutations were detected in seven families (19.4%). Two mutations were found in BRCA1 and three in BRCA2. One of the mutations (BRCA2 4088insA) has not been detected elsewhere in Finland while the other four, 4216-2nt A-->G and 5370 C-->T in BRCA1 and 999del5 and 6503delTT in BRCA2, are recurrent Finnish founder mutations. These results add to the evidence of the geographical differences in distribution of Finnish BRCA1/BRCA2 mutations. This screen also provides further evidence for the presumption that the majority of Finnish BRCA1/BRCA2 founder mutations have been found and that the proportion of BRCA1/BRCA2 mutations in Finnish breast/ovarian cancer families is around 20%.

Development of colorectal tumors in colonoscopic surveillance in Lynch syndrome

BACKGROUND & AIMS

Mutation carriers in Lynch syndrome families have a high risk for developing colorectal cancer during their lifetime. This study was designed to assess the cumulative risk for the development of colorectal adenoma or carcinoma in prospective colonoscopic surveillance.

METHODS

Data from the Finnish Hereditary Colorectal Cancer Registry electronic database on 420 Lynch syndrome mutation carriers without previous colorectal tumors were reviewed. Between March 1982 and May 2005 the mutation carriers underwent a total of 1252 colonoscopies. The total follow-up time was 3150 years (mean, 6.7 y/patient).

RESULTS

The cumulative risk of adenoma by age 60 was estimated as 68% (95% confidence interval [CI], 50%-80%) in men and 48% (95% CI, 29%-62%) in women. The estimated cumulative risk up to age 60 years for the development of cancer found as a result of surveillance at an interval of 2-3 years was 35% (95% CI, 16%-49%) in men and 22% (95% CI, 7%-34%) in women. Half of the adenomas were located proximal to the splenic flexure. Extracolonic cancer was diagnosed in 73 patients (18%).

CONCLUSIONS

Adenoma would appear to be the most important lesion preceding cancer formation in Lynch syndrome and removal of adenomas decreases the risk for colorectal cancer (CRC). The Finnish surveillance protocol of colonoscopies at 2- to 3-year intervals facilitates patient adherence but includes an essential risk for CRC up to 60 years of age, but without CRC-related mortality when the surveillance instructions are followed.

MLH1 and MSH2 mutations in Colombian families with hereditary nonpolyposis colorectal cancer (Lynch syndrome)--description of four novel mutations

This study searched for mutations in the MLH1 and MSH2 genes in 23 unrelated Colombian families with suspected hereditary nonpolyposis colorectal cancer (HNPCC). The families were grouped according to the fulfillment of the Amsterdam II criteria or the Bethesda guidelines. We screened all probands by single-strand conformational polymorphism (SSCP) and direct DNA sequencing. Eleven families fulfilled the Amsterdam criteria II and 12 families the Bethesda guidelines. Germline mutations were detected in 11 families, which corresponds to a mutation detection rate of 48%. When only families fulfilling the Amsterdam II criteria were analyzed, the mutation detection rate rose to 82%. Only 8% of the mutation detection rate was found in families following the Bethesda guidelines. Three mutations were shared by two different families, which corresponds to a total of eight different mutations, seven of them found in the MLH1 gene and one in the MSH2 gene. We have identified four mutations that have not been previously reported to the International Collaborative Group of HNPCC. Three of these are pathogenic, a single base substitution (C > T) at codon 640, exon 17, a G deletion at codon 619, exon 16 and in the MLH1 gene and a two-nucleotide deletion (TG) at codon 184, exon 3 in the MSH2. Also, an unclassified variant, a substitution (C > G) at the codon 141, exon 5 of the MLH1, was detected.

An Autosome-Wide Scan for Linkage Disequilibrium–Based Association in Sporadic Breast Cancer Cases in Eastern Finland: Three Candidate Regions Found

Breast cancer is the most common of cancers among women in industrialized countries. Many of breast cancer risk factors are known, but the majority of the genetic background is still unknown. Linkage disequilibrium–based association is a powerful tool for mapping disease genes and is suitable for mapping complex traits in founder populations. We report the results of a two-stage, autosome-wide scan for LD with breast cancer. Our aim was to identify genetic risk factors for sporadic breast cancer in an eastern Finnish population. Our case-control set is from the province of northern Savo in the late-settlement area of eastern Finland. This population is relatively young and genetically homogeneous. We used 435 autosomal microsatellite markers spaced by an average of 10 cM in a set of 49 breast cancer cases and 50 controls. In the first-stage scan, we found 21 markers in LD with breast cancer (Ps = 0.003-0.046, Fisher's exact test). In the second-stage scan with markers flanking 21 positive loci, four significant markers were found (Ps = 0.013-0.046, Fisher's exact test). Haplotype analysis using global score method with two, three, or four markers also revealed four positive marker combinations (simulated P for global score = 0.003-0.021). Our results suggest breast cancer–associated regions on 3p26, 11q23, and 22q13.1 in an eastern Finnish population.

Reconstruction of ancestral haplotypes in a 12-generation schizophrenia pedigree

We searched for candidate chromosomal regions inherited identical by descent in 19 patients suffering from schizophrenia or schizoaffective disorder that are related 12 generations back, to an ancestral couple born in the middle of the seventeenth century. To accomplish this goal, we constructed complete chromosomal haplotypes for each patient using genotype data from 450 markers. In total, 12 haplotype regions (with sizes ranging from 0.6 to 10.9 cM) constituted by three markers each were identical in three or more of the affected individuals. The largest genomic segment was located on 6q25, a region previously shown to be significantly more frequent in patients than controls, and proposed to contain a schizophrenia susceptibility locus. For the remaining 11 candidate haplotypes, we estimated haplotype frequencies from all the 43 affected members collected from the same family and 46 unrelated control individuals. This analysis indicated that at least four of the 11 candidate haplotypes are ancestral, since the frequencies were significantly higher in patients than in controls. Five additional haplotypes showed higher estimated frequencies in the patients but the differences were not significant. Interestingly, five of these 11 genomic regions are located in, or close to, candidate regions previously suggested to contain susceptibility genes for schizophrenia. The regions are 5q21-23, 8p21-22, 10p13-15, 13q12-13 and 22q12-13. Several of these haplotypes are probably ancestral linkage disequilibrium blocks inherited from the original couple. There exists, however, the possibility that one or more of these regions harbour schizophrenia susceptibility loci that may have epistatic interactions among them.

Linkage disequlibrium in the DTNBP1 (dysbindin) gene region and on chromosome 1p36 among psychotic patients from a genetic isolate in Israel: findings from identity by descent haplotype sharing analysis

Several genes have been reported recently to be associated with schizophrenia and bipolar disorder. Because of the complexity of the inheritance of these disorders, there is an urgent need to replicate these findings and to search for additional candidate genes. The study of genetic isolates is a powerful technique that may overcome some of the obstacles caused by genetic heterogeneity and ambiguity of phenotype definition. Identity by descent (IBD) haplotype sharing analysis in these populations may be used to detect mutations within shared haplotypes in smaller samples of affected individuals. In this study, we used IBD haplotype sharing analysis to replicate positive linkage and association findings in psychotic disorders, and to identify other regions of interest. Fifty-two patients with major psychiatric disorders from a genetically isolated village in Israel were studied. By studying eight Y chromosome markers, we were able to confirm the oral tradition of members of this isolate regarding a common paternal origin. Three hundred fifty nine microsatellite markers on 9 candidate chromosomes were genotyped, and haplotypes were reconstructed using information from family members. Two highly significant (P < 0.0001) peaks of haplotype sharing were found. One was for psychotic patients with any diagnosis at the location of dysbindin, a gene previously associated with schizophrenia. The other peak was for patients with schizophrenia on chromosome 1p36. Thus, this study both replicates an earlier finding and points to a novel region of interest, which might be unique to this population.

Haplotype associations define target regions for susceptibility loci in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by diverse and variable clinical manifestations. The etiology of SLE is still unknown, but both environmental and genetic factors are involved. Recent genome-wide scans and candidate genes studies in different ethnic groups have already suggested susceptibility loci for SLE, but most of the genetic component remains unexplained. We have previously conducted a genome-wide scan in 35 Finnish families multiply affected with SLE. With 417 microsatellite markers, we detected suggestive linkage in regions on chromosomes 6q and 14q as well as HLA on 6p. The 14q locus has also been implicated in three previous genome scans on SLE, whereas a partially overlapping region on 6q was implicated in one previous study. In an effort to obtain additional evidence for susceptibility loci on 6q and 14q and in order to refine their positions, we performed fine mapping at 1 cM density across the suggestive regions of linkage. Our results show evidence for excess sharing of a haplotype on 14q and excess transmission of a haplotype on 6q. Our results are compatible with the idea of a founder effect for susceptibility genes in SLE in central eastern Finland and suggest a path to the isolation of the putative susceptibility genes.

Evidence for allelic association on chromosome 3q25-27 in families with autism spectrum disorders originating from a subisolate of Finland

Recent molecular studies on autism and related disorders have supported a multilocus etiology for the disease spectrum. To maximize genetic and cultural homogeneity, we have focused our molecular studies to families originating from a subisolate of Central Finland. Genealogical studies enabled the identification of a megapedigree comprising of 12 core families with autism and Asperger syndrome (AS). We analyzed two chromosomal regions on Iq and 3q showing highest lod scores in our genome-wide scan, as well as the AUTS1 locus on chromosome 7q. For markers on 3q25-27, more significant association was observed in families from subisolate compared to families from the rest of Finland. In contrast, no clear evidence for association on AUTS1 locus was obtained. The wide interval showing association, in particular, on chromosome 3q suggests a locus for autism spectrum of disorders on this chromosomal region.

Genetic alterations and MSI status in primary, synchronous, and metachronous tumors in a family with hereditary nonpolyposis colorectal cancer (HNPCC)

In colorectal cancer, different levels of microsatellite instability (MSI) have been described: high-frequency MSI, low-frequency MSI, and stable microsatellites. MSI-H characterizes a unique clinical and pathologic phenotype known as hereditary nonpolyposis colorectal cancer syndrome (HNPCC). In this case, an increased incidence of synchronous and metachronous tumors has been reported, but there are few reports with standardized criteria of MSI in HNPCC-associated tumors. The authors attempted to establish whether tumors of the HNPCC spectrum with different levels of MSI could predict the development of metachronous carcinomas. We have examined the levels of MSI at loci frequently affected in colorectal cancers in primary, synchronous, and metachronous tumors in a family that fulfils the Amsterdam criteria for HNPCC. This family presents colorectal cancers, HNPCC-extracolonic tumors (endometrial and ureter), and tumors (breast and bladder) not described in the HNPCC spectrum. The tumors exhibited MSI-H, irrespective of their location and regardless whether they were primary, synchronous, or metachronous, with the only exception of both endometrial tumors that showed low-frequency MSI tumors (MSI-L). Our results suggest that not only colorectal tumors with MSI-H result in a potential marker for the determination of high-risk individuals for metachronous and synchronous tumors, but also MSI-L endometrial tumors might be considered as indicative of high-risk individuals.

Human population genetics: lessons from Finland

A population of about 5 million at the northern corner of Europe is unlikely to arouse the attention of the human genetics community, unless it offers something useful for others to learn. A combination of coincidences has finally made this population one that, out of proportion for its size, has by example shaped research in human disease genetics. This chapter summarizes advances made in medical genetics that are based on research facilitated by Finland's population structure. The annotation of the human genome for its polymorphism and involvement in disease is not over; it is, therefore, of interest to assess whether genetic studies in populations such as the Finnish might help in the remaining tasks.

DNA mismatch repair defects: role in colorectal carcinogenesis

The inactivation of the DNA mismah repair (MMR) system, which is associated with the predisposition to the hereditary non-polyposis colorectal cancer (HNPCC), has also been documented in nearly 20% of the sporadic colorectal cancers. These tumors are characterized by a high frequency of microsatellite instability (MSI(+) phenotype), resulting from the accumulation of small insertions or deletions that frequently arise during replication of these short repeated sequences. A germline mutation of one of the two major MMR genes (hMSH2 or hMLH1) is found in half to two-thirds of the patients with HNPCC, whereas in sporadic cases hypermethylation of the hMLH1 promoter is the major cause of the MMR defect. Germline mutations in hMSH6 are rare and rather confer predisposition to late-onset familial colorectal cancer, and frequent extracolonic tumors. Yet, the genetic background of a number of HNPCC patients remains unexplained, indicating that other genes participate in MMR and play important roles in cancer susceptibility. The tumor-suppressor genes that are potential targets for the MSI-driven mutations because they contain hypermutable repeated sequences are likely to contribute to the etiology and tissue specificity of the MSI-associated carcinogenesis. Because the prognosis and the chemosensitivity of the MSI(+) colorectal tumors differ from those without instability, the determination of the MSI phenotype is expected to improve the clinical management of patients. This review gives an overview of various aspects of the biochemistry and genetics of the DNA mismah repair system, with particular emphasis in its role in colorectal carcinogenesis.

Talking tumours: histories from sequences

The history of a tumour is currently inferred from its morphology. However, progression may be variable between similar appearing tumours, and some critical events may be difficult to see. It has become increasingly apparent that histories are also written within sequences. Every tumour likely records its own progression within its genome. In the future, it may be possible to read the past based on these sequences. A critical issue is whether these autobiographies will recapitulate morphology or whether they reveal unexpected ghosts.

Nationwide cancer family ascertainment using Finnish Cancer Registry data on family names and places of birth for 35,761 prostate cancer patients

Identification of predisposition loci to complex diseases, such as prostate cancer, requires high-quality family material, the ascertainment of which is often laborious, time-consuming and inaccurate with conventional methods. Here, we describe a new method for rapid, nationwide cancer family ascertainment using Finnish Cancer Registry data on 35,761 prostate cancer cases over a 40-year period. As members of a prostate cancer family are likely to share the same family name and place of birth, we stratified all prostate cancer cases by these 2 parameters (10,721 different names and 596 municipalities). Data were compared with the distribution of family names and places of birth for all 3.3 million Finnish men to derive standardized prevalence ratios (SPRs). A significantly elevated SPR of prostate cancer was detected for 468 (1.6%) of the 28,459 evaluable combinations of family name and place of birth. Of the 20 highest SPR values, 19 corresponded to true nuclear families, most of these having 3 or more affected cases. Two-thirds of our 50 previously established Finnish prostate cancer families were classified among this 1.6% fraction of the highest SPR values. Finally, many of the highest SPR values originated from municipalities in southern and south-western Finland. To explore whether such clusters could highlight local founder effects, we applied genealogical research to link together several families with elevated SPRs and identified an extended family with 20 prostate cancer cases with common ancestors in the early seventeenth century. In summary, a rapid novel method was developed and validated for identification of prostate cancer families from nationwide cancer registry data and for the identification of putative regional founder effects.

Molecular epidemiology of hereditary nonpolyposis colorectal cancer in Finland

The population frequency of germline mutations predisposing to hereditary nonpolyposis colorectal cancer (HNPCC) is unknown. Several epidemiological studies have addressed the problem, and estimates on the proportion of the total colorectal cancer burden accounted for by HNPCC have varied between 0.5% and 13%. In the absence of any clinical diagnostic hallmarks, the definition of HNPCC is based on family history. The problem in defining the syndrome is reflected in the wide range of frequency estimates. The molecular background of HNPCC has recently been clarified. Defects in a total of five different mismatch repair genes have been associated with the syndrome. Tumors associated with HNPCC display microsatellite instability (or replication error, RER). RER analysis followed by germline mutation analysis in the mismatch repair genes allows molecular diagnosis in a proportion of HNPCC patients. These diagnostic methods are likely to contribute to our understanding of the epidemiology of HNPCC. In Finland, the centralized health care system, population history, and recent advances in molecular genetic research have together created tools to evaluate the molecular epidemiology of HNPCC in the country.

A common MSH2 mutation in English and North American HNPCC families: origin, phenotypic expression, and sex specific differences in colorectal cancer

The frequency, origin, and phenotypic expression of a germline MSH2 gene mutation previously identified in seven kindreds with hereditary non-polyposis cancer syndrome (HNPCC) was investigated. The mutation (A-->T at nt943+3) disrupts the 3' splice site of exon 5 leading to the deletion of this exon from MSH2 mRNA and represents the only frequent MSH2 mutation so far reported. Although this mutation was initially detected in four of 33 colorectal cancer families analysed from eastern England, more extensive analysis has reduced the frequency to four of 52 (8%) English HNPCC kindreds analysed. In contrast, the MSH2 mutation was identified in 10 of 20 (50%) separately identified colorectal families from Newfoundland. To investigate the origin of this mutation in colorectal cancer families from England (n=4), Newfoundland (n=10), and the United States (n=3), haplotype analysis using microsatellite markers linked to MSH2 was performed. Within the English and US families there was little evidence for a recent common origin of the MSH2 splice site mutation in most families. In contrast, a common haplotype was identified at the two flanking markers (CA5 and D2S288) in eight of the Newfoundland families. These findings suggested a founder effect within Newfoundland similar to that reported by others for two MLH1 mutations in Finnish HNPCC families. We calculated age related risks of all, colorectal, endometrial, and ovarian cancers in nt943+3 A-->T MSH2 mutation carriers (n=76) for all patients and for men and women separately. For both sexes combined, the penetrances at age 60 years for all cancers and for colorectal cancer were 0.86 and 0.57, respectively. The risk of colorectal cancer was significantly higher (p<0.01) in males than females (0.63 v 0.30 and 0.84 v 0.44 at ages 50 and 60 years, respectively). For females there was a high risk of endometrial cancer (0.5 at age 60 years) and premenopausal ovarian cancer (0.2 at 50 years). These intersex differences in colorectal cancer risks have implications for screening programmes and for attempts to identify colorectal cancer susceptibility modifiers.

Linkage disequilibrium mapping in isolated populations: the example of Finland revisited

Linkage disequilibrium analysis can provide high resolution in the mapping of disease genes because it incorporates information on recombinations that have occurred during the entire period from the mutational event to the present. A circumstance particularly favorable for high-resolution mapping is when a single founding mutation segregates in an isolated population. We review here the population structure of Finland in which a small founder population some 100 generations ago has expanded into 5.1 million people today. Among the 30-odd autosomal recessive disorders that are more prevalent in Finland than elsewhere, several appear to have segregated for this entire period in the "panmictic" southern Finnish population. Linkage disequilibrium analysis has allowed precise mapping and determination of genetic distances at the 0.1-cM level in several of these disorders. Estimates of genetic distance have proven accurate, but previous calculations of the confidence intervals were too small because sampling variation was ignored. In the north and east of Finland the population can be viewed as having been "founded" only after 1500. Disease mutations that have undergone such a founding bottleneck only 20 or so generations ago exhibit linkage disequilibrium and haplotype sharing over long genetic distances (5-15 cM). These features have been successfully exploited in the mapping and cloning of many genes. We review the statistical issues of fine mapping by linkage disequilibrium and suggest that improved methodologies may be necessary to map diseases of complex etiology that may have arisen from multiple founding mutations.

Microsatellite instability and loss of heterozygosity at DNA mismatch repair gene loci occurs during hepatic carcinogenesis

DNA mismatch repair is an important mechanism involved in maintaining the fidelity of genomic DNA. Defective DNA mismatch repair is implicated in a variety of gastrointestinal and other tumors; however, its role in hepatocellular carcinoma (HCC) has not been assessed. Formalin-fixed, paraffin-embedded archival pathology tissues from 46 primary liver tumors were studied by microdissection and microsatellite analysis of extracted DNA to assess the degree of microsatellite instability, a marker of defective mismatch repair, and to determine the extent and timing of allelic loss of two DNA mismatch repair genes, human Mut S homologue-2 (hMSH2) and human Mut L homologue-1 (hMLH1), and the tumor suppressor genes adenomatous polyposis coli gene (APC), p53, and DPC4. Microsatellite instability was detected in 16 of the tumors (34.8%). Loss of heterozygosity at microsatellites linked to the DNA mismatch repair genes, hMSH2 and/or hMLH1, was found in 9 cases (19.6%), usually in association with microsatellite instability. Importantly, the pattern of allelic loss was uniform in 8 of these 9 tumors, suggesting that clonal loss had occurred. Moreover, loss at these loci also occurred in nonmalignant tissue adjacent to 4 of these tumors, where it was associated with marked allelic heterogeneity. There was relatively infrequent loss of APC, p53, or DPC4 loci that appeared unrelated to loss of hMSH2 or hMLH1 gene loci. Loss of heterozygosity at hMSH2 and/or hMLH1 gene loci, and the associated microsatellite instability in premalignant hepatic tissues suggests a possible causal role in hepatic carcinogenesis in a subset of hepatomas.

Hereditary nonpolyposis colorectal cancer: an update

Sporadic cancer develops approximately at 65 years of age. Epidemiologic data suggest that dietary factors probably are the most influential in colorectal carcinogenesis. In contrast, individuals who have relatives with colorectal neoplasia have an increased risk of these tumors themselves, which will appear earlier in life. The actual incidence of hereditary colorectal cancer is unknown. However, the incidence is much higher compared with well-known hereditary colorectal diseases, such as familial adenomatous polyposis.

OBJECTIVE

An overview of the recent progress in the field of both clinical and basic research on hereditary colorectal cancer must be made.

MATERIALS AND METHODS

Twenty-two family pedigrees were analyzed at Hamamatsu University School of Medicine, including the largest family pedigree in Japan, which contained 24 cases of colorectal cancer occurring over five generations. In 1995, when the International Symposium on Hereditary Cancer was held in Hamamatsu, 4,109 family pedigrees were investigated and analyzed, including 394 cases in 109 family pedigrees that met the Amsterdam Minimum Criteria. Information was collected by sending questionnaires to major hospitals in Japan. Basic updated data presented at the eighth and ninth International Collaborative Group on Hereditary Colorectal Cancer were also quoted.

RESULTS AND CONCLUSIONS

Because of the discovery of mismatch repair genes as that responsible for hereditary nonpolyposis colorectal cancer, modification of the Amsterdam Criteria is necessary. Replication error, as a mutator phenotype of mismatch repair genes, is a useful predictor of second primary malignancies. Surveillance or prophylactic surgery is still a controversial issue.

Molecular biology of colorectal cancer

Colorectal cancer is a significant cause of morbidity and mortality in Western populations. This cancer develops as a result of the pathologic transformation of normal colonic epithelium to an adenomatous polyp and ultimately an invasive cancer. The multistep progression requires years and possibly decades and is accompanied by a number of recently characterized genetic alterations. Mutations in two classes of genes, tumor-suppressor genes and proto-oncogenes, are thought to impart a proliferative advantage to cells and contribute to development of the malignant phenotype. Inactivating mutations of both copies (alleles) of the adenomatous polyposis coli (APC) gene--a tumor-suppressor gene on chromosome 5q--mark one of the earliest events in colorectal carcinogenesis. Germline mutation of the APC gene and subsequent somatic mutation of the second APC allele cause the inherited familial adenomatous polyposis syndrome. This syndrome is characterized by the presence of hundreds to thousands of colonic adenomatous polyps. If these polyps are left untreated, colorectal cancer develops. Mutation leading to dysregulation of the K-ras protooncogene is also thought to be an early event in colon cancer formation. Conversely, loss of heterozygosity on the long arm of chromosome 18 (18q) occurs later in the sequence of development from adenoma to carcinoma, and this mutation may predict poor prognosis. Loss of the 18q region is thought to contribute to inactivation of the DCC tumor-suppressor gene. More recent evidence suggests that other tumor-suppressor genes--DPC4 and MADR2 of the transforming growth factor beta (TGF-beta) pathway--also may be inactivated by allelic loss on chromosome 18q. In addition, mutation of the tumor-suppressor gene p53 on chromosome 17p appears to be a late phenomenon in colorectal carcinogenesis. This mutation may allow the growing tumor with multiple genetic alterations to evade cell cycle arrest and apoptosis. Neoplastic progression is probably accompanied by additional, undiscovered genetic events, which are indicated by allelic loss on chromosomes 1q, 4p, 6p, 8p, 9q, and 22q in 25% to 50% of colorectal cancers. Recently, a third class of genes, DNA repair genes, has been implicated in tumorigenesis of colorectal cancer. Study findings suggest that DNA mismatch repair deficiency, due to germline mutation of the hMSH2, hMLH1, hPMS1, or hPMS2 genes, contributes to development of hereditary nonpolyposis colorectal cancer. The majority of tumors in patients with this disease and 10% to 15% of sporadic colon cancers display microsatellite instability, also know as the replication error positive (RER+) phenotype. This molecular marker of DNA mismatch repair deficiency may predict improved patient survival. Mismatch repair deficiency is thought to lead to mutation and inactivation of the genes for type II TGF-beta receptor and insulin-like growth-factor II receptor. Individuals from families at high risk for colorectal cancer (hereditary nonpolyposis colorectal cancer or familial adenomatous polyposis) should be offered genetic counseling, predictive molecular testing, and when indicated, endoscopic surveillance at appropriate intervals. Recent studies have examined colorectal carcinogenesis in the light of other genetic processes. Telomerase activity is present in almost all cancers, including colorectal cancer, but rarely in benign lesions such as adenomatous polyps or normal tissues. Furthermore, genetic alterations that allow transformed colorectal epithelial cells to escape cell cycle arrest or apoptosis also have been recognized. In addition, hypomethylation or hypermethylation of DNA sequences may alter gene expression without nucleic acid mutation.

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.

Age and origin of two common MLH1 mutations predisposing to hereditary colon cancer

Two mutations in the DNA mismatch repair gene MLH1, referred to as mutations 1 and 2, are frequent among Finnish kindreds with hereditary nonpolyposis colorectal cancer (HNPCC). In order to assess the ages and origins of these mutations, we constructed a map of 15 microsatellite markers around MLH1 and used this information in haplotype analyses of 19 kindreds with mutation 1 and 6 kindreds with mutation 2. All kindreds with mutation 1 showed a single allele for the intragenic marker D3S1611 that was not observed on any unaffected chromosome. They also shared portions of a haplotype of 4-15 markers encompassing 2.0-19.0 cM around MLH1. All kindreds with mutation 2 shared another allele for D3S1611 and a conserved haplotype of 5-14 markers spanning 2.0-15.0 cM around MLH1. The degree of haplotype conservation was used to estimate the ages of these two mutations. While some recessive disease genes have been estimated to have existed and spread for as long as thousands of generations worldwide and hundreds of generations in the Finnish population, our analyses suggest that the spread of mutation 1 started 16-43 generations (400-1,075 years) ago and that of mutation 2 some 5-21 generations (125-525 years) ago. These datings are compatible with our genealogical results identifying a common ancestor born in the 16th and 18th century, respectively. Overall, our results indicate that all Finnish kindreds studied to date showing either mutation 1 or mutation 2 are due to single ancestral founding mutations relatively recent in origin in the population. Alternatively, the mutations arose elsewhere earlier and were introduced in Finland more recently.

Polymorphism in the cytochrome P450 2E1 gene and alcohol-induced disorders of human spermatogenesis

The association between alcohol-induced disorders of human spermatogenesis and four restriction fragment polymorphisms (DraI, MspI, PstI and RsaI) of the cytochrome P450 2E1 gene was investigated in an autopsy study on 254 men. Acquaintances were interviewed and the mean daily alcohol consumption of the subjects was calculated on the basis of the interviews. Spermatogenesis score and testicular morphology were assessed by light-microscopy, and cytochrome 2E1 polymorphic genotypes were determined using the polymerase chain reaction. Of the 204 heavy-drinking men, 42 (20.6%) men had normal spermatogenesis (p < 0.001, compared to moderate drinkers). Partial spermatogenic arrest was observed in 76 (37.3%) men and complete spermatogenic arrest in 79 (38.7%) men (p < 0.001, compared to moderate drinkers), whereas seven men (3.4%) had Sertoli cell only syndrome. The overall allelic frequencies for the common and rare polymorphic alleles were 0.98 and 0.02 (MspI) and 0.99 and 0.01 (PstI and RsaI), respectively. No associations between heterozygosity in the MspI, PstI or RsaI loci, or the allelic frequencies of common and rare alleles, and disorders of spermatogenesis were observed. The allelic frequencies for the common and rare polymorphic alleles in the DraI locus were 0.90 and 0.10, respectively. No significant difference was observed, either among moderate or heavy drinkers, in the frequency of the rare allele between men with disorders of spermatogenesis and those with normal spermatogenesis in the respective group, although men with disorders of spermatogenesis in general had a slightly lower frequency of the rare allele when compared to those with normal spermatogenesis. In conclusion, we were unable to demonstrate a significant association between any polymorphisms in the CYP2E1 gene and disorders of spermatogenesis. RsaI, MspI and PstI polymorphisms were extremely rare in our population and could thus possibly be excluded as reasons for genetic susceptibility to disorders of spermatogenesis in our series.

Complex genetic predisposition to cancer in an extended HNPCC family with an ancestral hMLH1 mutation

Hereditary non-polyposis colorectal cancer (HNPCC) is characterised by a genetic predisposition to develop colorectal cancer at an early age and, to a lesser degree, cancer of the endometrium, ovaries, urinary tract, and organs of the gastrointestinal tract other than the colon. In the majority of families the disease is linked to mutations in one of the two mismatch repair genes, hMSH2 or hMLH1. We have found a novel hMLH1 nonsense mutation in a Swiss family with Lynch syndrome, which has been transmitted through at least nine generations. A different tumour spectrum of neoplasms of the skin, soft palate, breast, duodenum, and pancreas was observed in three branches of this family, where there was a virtual absence of colonic tumours. The hMLH1 mutation could not be detected in members of these branches suggesting that at least a second genetic defect predisposing to cancer is segregating in part of the kindred.

Glutathione S-transferase-M1 'null' genotype and alcohol-induced disorders of human spermatogenesis

The association between alcohol-induced disorders of human spermatogenesis and glutathione S-transferase-M1 genotype was investigated in an autopsy study comprising 271 subjects, including interviews with relatives or close acquaintances on the alcohol consumption of the deceased. Of the 50 moderate drinking men (reported mean daily alcohol consumption < 40 g), 21 (42.0%) had normal spermatogenesis, whereas 24 men (48.0%) had partial, and five (10.0%) complete arrest of spermatogenesis. Of the 21 men with normal spermatogenesis, nine (42.9%) had GST M1 'null' genotype, while this genotype was found in 13 (44.8%) of the 29 men with partial or complete spermatogenic arrest. Of 212 heavy-drinking men (reported mean daily alcohol consumption > 80 g), only 45 (21.2%) had normal spermatogenesis, whereas 77 (36.3%) had partial spermatogenic arrest. Complete arrest of spermatogenesis was found in 81 men (38.2%) and nine men had Sertoli-cell-only syndrome (4.2%). Of the 45 heavy drinkers with normal spermatogenesis, 27 (60%) men had GST M1 'null' genotype (OR 2.7 with 95% confidence intervals: 1.0-4.0, when compared to those with disorders of spermatogenesis). The frequency of GST M1 'null' genotype in heavy drinkers with normal spermatogenesis also differed from that of corresponding moderate drinkers, whereas the frequency of GST M1 'null' genotype in heavy drinkers with disorders of spermatogenesis was similar to moderate drinkers with or without disorders of spermatogenesis. The finding that > 20% of men in the heavy-drinking group had normal spermatogenesis suggests individual variations in sensitivity to alcohol-induced disorders of this process. Heavy drinkers with GST M1 'null' genotype were slightly less prone to develop disorders of spermatogenesis. Thus, the GST M1 locus may be associated with susceptibility to develop alcohol-induced disorders of spermatogenesis.

Use of linkage disequilibrium approaches to map genes for bipolar disorder in the Costa Rican population

Linkage disequilibrium (LD) analysis provides a powerful means for screening the genome to map the location of disease genes, such as those for bipolar disorder (BP). As described in this paper, the population of the Central Valley of Costa Rica, which is descended from a small number of founders, should be suitable for LD mapping; this assertion is supported by reconstruction of extended haplotypes shared by distantly related individuals in this population suffering low-frequency hearing loss (LFHL1), which has previously been mapped by linkage analysis. A sampling strategy is described for applying LD methods to map genes for BP, and clinical and demographic characteristics of an initially collected sample are discussed. This sample will provide a complement to a previously collected set of Costa Rican BP families which is under investigation using standard linkage analysis.

Mapping of the variegate porphyria (VP) gene: contradictory evidence for linkage between VP and microsatellite markers at chromosome 14q32

The gene for variegate porphyria (VP), an autosomal dominant disease with a high prevalance in South Africa, evidently due to a founder effect, was previously mapped to chromosome 14q32. In the current study this localization was evaluated by linkage and haplotype analyses using microsatellite markers spanning a region of more than 20 cM on chromosome 14q32. In many recent studies linkage disequilibrium between disease and marker loci has been utilized to map genes in founder populations, but we could not find any association between VP and the markers used in this study. Our data suggest that the allocation of VP to chromosome 14q32 may be incorrect.

Hereditary nonpolyposis colorectal cancer: review of clinical, molecular genetics, and counseling aspects

Lynch syndrome, or hereditary nonpolyposis colon cancer (HNPCC), is an autosomal-dominant disease accounting for approximately 1-5% of all colorectal cancer cases. Due to the lack of pathognomonic morphological or biomolecular markers, HNPCC has traditionally posed unique problems to clinicians and geneticists alike, both in terms of diagnosis and clinical management. Recently, novel insight into the pathogenesis of this syndrome has been provided by the identification of its molecular basis. In HNPCC families, germline mutations in any of four genes encoding proteins of a specialized DNA repair system, the mismatch repair, predispose to cancer development. Mutations in mismatch repair genes lead to an overall increase of the mutation rate and are associated with a phenotype of length instability of microsatellite loci. The present report summarizes the clinicopathological aspects of HNPCC and reviews the most recent molecular and biochemical findings.

Genetic mapping using haplotype, association and linkage methods suggests a locus for severe bipolar disorder (BPI) at 18q22-q23

Manic depressive illness, or bipolar disorder (BP), is characterized by episodes of elevated mood (mania) and depression. We designed a multistage study in the genetically isolated population of the Central Valley of Costa Rica to identify genes that promote susceptibility to severe BP (termed BPI), and screened the genome ot two Costa Rican BPI pedigrees (McInnes et al., submitted). We considered only individuals who fulfilled very stringent diagnostic criteria for BPI to be affected. The strongest evidence for a BPI locus was observed in 18q22-q23. We tested 16 additional markers in this region and seven yielded peak lod scores over 1.0. These suggestive lod scores were obtained over a far greater chromosomal length (about 40 cM) than in any other genome region. This localization is supported by marker haplotypes shared by 23 of 26 BPI affected individuals studied. Additionally, marker allele frequencies over portions of this region are significantly different in the patient sample from those of the general Costa Rican population. Finally, we performed an analysis which made use of both the evidence for linkage and for association in 18q23, and we observed significant lod scores for two markers in this region.

Overview of natural history, pathology, molecular genetics and management of HNPCC (Lynch Syndrome)

Hereditary non-polyposis colorectal cancer (HNPCC) predisposes to cancers of the colon, endometrium and several other extra-colonic sites in the absence of premonitory physical stigmata (Muir-Torre syndrome excepted). Discovery of the several DNA mismatch repair genes (hMSH2, hMLH1, hPMS1, hPMS2) holds the potential for determining the cancer destiny of patients, theoretically in utero. Pre-symptomatic DNA testing is now possible in patients from HNPCC families and will be clinically available once inexpensive and simple tests for these germ-line mutations have been effected. Genetic counseling will be mandatory, given the myriad socio-psychological, insurance, and potentially other personal issues which may impact this knowledge. New findings in the pathology of HNPCC, particularly an increased frequency of interval cancers and the likely accelerated rate of the adenoma to cancer sequence, indicate the need for more frequent colonoscopic surveillance with an option for prophylactic subtotal colectomy in germ-line-positive individuals.

CpG dinucleotides in the hMSH2 and hMLH1 genes are hotspots for HNPCC mutations

Hereditary nonpolyposis colon cancer (HN-PCC) is an autosomally inherited predisposition to cancer that has recently been linked to defects in the human mismatch repair genes hMSH2 and hMLH1. The identification of the causative mutations in HNPCC families is desirable, since it confirms the diagnosis and allows the carrier status of unaffected relatives at risk to be determined. We report six different new mutations identified in the hMSH2 and hMLH1 genes of Russian and Moldavian HNPCC families. Three of these mutations occur in CpG dinucleotides and lead to a premature stop codon, a splicing defect or an amino-acid substitution in an evolutionary conserved residue. Analysis of a compilation of published mutations including our new data suggests that CpG dinucleotides within the coding regions of the hMSH2 and hMLH1 genes are hotspots for single base-pair substitutions.

Analysis of mismatch repair genes in hereditary non-polyposis colorectal cancer patients

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant disorder characterized by the early onset of colorectal cancer and linked to germline defects in at least four mismatch repair genes. Although much has been learned about the molecular pathogenesis of this disease, questions related to effective presymptomatic diagnosis are largely unanswered because of its genetic complexity. In this study, we evaluated tumors from 74 HNPCC kindreds for genomic instability characteristic of a mismatch repair deficiency and found such instability in 92% of the kindreds. The entire coding regions of the five known human mismatch repair genes were evaluated in 48 kindreds with instability, and mutations were identified in 70%. This study demonstrates that a combination of techniques can be used to genetically diagnose tumor susceptibility in the majority of HNPCC kindreds and lays the foundation for genetic testing of this relatively common disease.

The Lynch Syndrome: Melding Natural History and Molecular Genetics to Genetic Counseling and Cancer Control

Hereditary nonpolyposis colorectal cancer (HNPCC), also referred to as Lynch syndromes I and II, is an autosomal, dominantly inherited disorder that accounts for approximately 5% of all colorectal cancers. While colorectal cancer is the most frequently occurring malignancy in HNPCC, other types of cancer occur with increased statistical significance. A better understanding of its natural history, particularly early age of onset and the pattern of multiple primary cancer excess, is essential for the diagnosis and management of HNPCC.

Diagnostic use of microsatellite instability in hereditary non-polyposis colorectal cancer

50 families with a history of colorectal cancer were divided according to whether criteria for hereditary non-polyposis colorectal cancer (HNPCC) were fulfilled totally (A, n = 19) or partly (B, n = 31) and stratified by the demonstration that at least half the cancers tested per family were positive for DNA replication errors (RER+). Accepted clinical and pathological characteristics of HNPCC were found to cluster within 12 A/RER+ families in which the mean number of affected individuals per family was 10.1. Reliance upon clinical data alone may result in over-diagnosis of HNPCC, in small families who just meet the minimum criteria, whereas underdiagnosis is rare. The criteria could be refined by inclusion of RER status.

Perspectives of identity by descent (IBD) mapping in founder populations

In a founder population patients with a genetic disease are likely to share predisposing genes from a common ancestor. We show that, depending on the distance of the relationship, patients are expected to share extended segments of DNA around the disease gene. Because of the size of the shared segment, a genomic search with DNA markers for such shared segments, identity by descent (IBD) mapping, can efficiently find the map position of genes, particularly due to genetic drift leading to reduction of heterogeneity and the large number of meioses that is implicitly observed. The statistical power of this method and the approximate cost are given as a function of the density of the map of tested markers and the number of generations since a common ancestor. Initial marker spacings between 5 and 15 centiMorgans are shown to be optimal. IBD mapping is applicable to many genetic diseases, because it does not presuppose a specific genetic model.

Founding mutations and Alu-mediated recombination in hereditary colon cancer

By screening members of Finnish families displaying hereditary nonpolyposis colorectal cancer (HNPCC) for predisposing germline mutations in MSH2 and MLH1, we show that two mutations in MLH1 together account for 63% (19/30) of kindreds meeting international diagnostic criteria. Mutation 1, originally detected as a 165-base pair deletion in MLH1 cDNA comprising exon 16, was shown to consist of a 3.5-kilobase genomic deletion most likely resulting from Alu-mediated recombination. Mutation 2 destroys the splice acceptor site of exon 6. A simple diagnostic test based on polymerase chain reaction was designed for both mutations. Our results show that these two ancestral founding mutations account for a majority of Finnish HNPCC kindreds and represent the first report of Alu-mediated recombination causing a prevalent, dominantly inherited predisposition to cancer.