A novel missense MSH2 gene mutation in a patient of a Korean family with hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant cancer-susceptible syndrome that predisposes to the early development of colorectal cancer. Germline mutations in DNA mismatch repair genes, particularly MLH1 and MSH2, are associated with the clinical phenotype of HNPCC. A previously unreported, novel missense mutation in exon 3 of the MSH2 gene (c.380A>T) was identified in the proband and a different missense mutation in exon 3 of MSH2 gene (c.505A>G) was noted in the mother, with a mutual splice mutation in intron 12 of the MSH2 gene in the proband, mother, and younger brother. Here, we report the clinical implications of a novel mutation in a patient with early-onset colorectal cancer and the significance of a common underlying splice site mutation occurring within a family with HNPCC.     

Stability of BAT26 in tumours of hereditary nonpolyposis colorectal cancer patients with MSH2 intragenic deletion

Colon cancers arising in most patients with hereditary nonpolyposis colorectal cancer (HNPCC) show microsatellite instability (MSI). BAT26, a quasimonomorphic polyA stretch located just 3' of MSH2 exon 5, is considered the most sensitive and specific marker of MSI. A total of 10 HNPCC families with large intragenic MSH2 deletions, encompassing exon 5 and intron 5, identified by multiplex ligation-dependent probe amplification (MLPA) were included in this study. The deletions under study were del1-16, del1-8, del1-7, del1-6, and del3-6, detected in 3, 1, 2, 3, and 1 families, respectively. Although all patients examined from these 10 families developed unstable tumours, 13/19 MSI-H tumours (68 %) surprisingly showed stability of BAT26. By MLPA and MSH2 sequence analyses of the BAT26-stable tumours, we demonstrated that the wild-type MSH2 allele was somatically inactivated by an identical large deletion, with complete loss of intron 5/BAT26 sequences at the tumour DNA level. We could infer that the apparent stability of BAT26 was due to the complete absence of target BAT26 sequences in the tumour sample, which results in exclusive amplification of contaminant normal DNA, containing a single copy of a wild-type stable BAT26 sequence. Identification of a subset of MSH2-related unstable tumours that are not recognized by analysis of BAT26 instability indicates that this marker should never be used alone for rapid MSI screening of HNPCC tumours. Moreover, our findings indicate that BAT26 stability in the context of MSI is strongly suggestive of the presence of a large intragenic MSH2 deletion.     

Seven novel MLH1 and MSH2 germline mutations in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent hereditary form of colorectal cancer and is caused by germline mutations in mismatch repair (MMR) genes. The majority of mutations occur in MLH1 and MSH2. We report hereby seven novel germline mutations in these two genes (five in MLH1 and two in MSH2). All mutations have been found in families fulfilling criteria of the Bethesda guidelines and four of which also fulfilled the Amsterdam criteria. We identified three insertions or deletions of 1 bp leading to premature stop codons (MLH1: c.341delC, c.1413‐1414insA; MSH2: c.1119delG) and three nonsense mutations (MLH1: c.67G>T [E23X], c.436C>T [Q146X]; MSH2: c.1857T>G [Y619X]). The corresponding tumors showed a high level of microsatellite instability (MSI‐H) and a complete loss of expression of the affected protein. In addition, a missense mutation in MLH1 was identified (c.1984A>C [T662P]). The respective tumor also showed a high level of microsatellite instability but a reduced, rather then lost, expression of the MLH1‐protein. This missense mutation was not found in 107 healthy control individuals and in 54 HNPCC patients. © 2001 Wiley‐Liss, Inc.     

Six novel heterozygous MLH1, MSH2, and MSH6 and one homozygous MLH1 germline mutations in hereditary nonpolyposis colorectal cancer

Most hereditary nonpolyposis colorectal cancer (HNPCC) cases are caused by germline mutations of mismatch repair (MMR) genes (i.e., MLH1, MSH2, or MSH6). Here we describe six novel mutations in patients referred for genetic assessment. All of these mutations lead to premature translation termination. Five single base pair deletions lead to frameshift (MLH1: g.38-39insCCCA, g.1971del.T; MSH2: g.163del.C, g.746del.A; MSH6: g.3320del.A) and one nonsense mutation in MSH2 g.1030C>T leads to a stop codon: p.Q344X. In one patient, the previously described MLH1 nonsense mutation g.806C>G was found in a homozygous state. In this patient, the familial histories of both the mother and father suggested HNPCC syndrome. This patient developed colon cancer at 22 years of age, suggesting a more aggressive phenotype. The results of our study provide further insight into the mutational spectrum of MMR genes in HNPCC families.     

Medullary carcinoma of the pancreas in a man with hereditary nonpolyposis colorectal cancer due to a mutation of the MSH2 mismatch repair gene

Pancreatic adenocarcinoma has been reported in kindreds with hereditary nonpolyposis colorectal cancer (HNPCC). Medullary carcinoma of the pancreas is a recently described rare variant of pancreatic adenocarcinoma. We describe a man with colorectal carcinoma who subsequently developed pancreatic medullary carcinoma. The tumor displayed microsatellite instability and loss of expression of the mismatch repair proteins MSH2 and MSH6. Mutational analysis of the mismatch repair genes MLH1 and MSH2 demonstrated a pathogenic nonsense mutation within the MSH2 gene, which is consistent with a diagnosis of HNPCC. This report adds support to an association between HNPCC and pancreatic adenocarcinoma displaying the medullary phenotype, suggesting that medullary features in a pancreatic carcinoma may point toward a genetic cancer predisposition. To our knowledge, this is the first reported case of medullary carcinoma of the pancreas in a patient with HNPCC due to a mutation of the MSH2 gene.     

Partial duplications of the MSH2 and MLH1 genes in hereditary nonpolyposis colorectal cancer

Numerous reports have highlighted the contribution of MSH2 and MLH1 genomic deletions to hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch's syndrome, but genomic duplications of these genes have been rarely reported. Using quantitative multiplex PCR of short fluorescent fragments (QMPSF), 962 and 611 index cases were, respectively, screened for MSH2 and MLH1 genomic rearrangements. This allowed us to detect, in 11 families, seven MSH2 duplications affecting exons 1-2-3, exons 4-5-6, exon 7, exons 7-8, exons 9-10, exon 11, and exon 15, and three MLH1 duplications affecting exons 2-3, exon 4 and exons 6-7-8. All duplications were confirmed by an independent method. The contribution of genomic duplications of MSH2 and MLH1 to HNPCC can therefore be estimated approximately to 1% of the HNPCC cases. Although this frequency is much lower than that of genomic deletions, the presence of MSH2 or MLH1 genomic duplications should be considered in HNPCC families without detectable point mutations.     

Four novel MSH2 and MLH1 frameshift mutations and occurrence of a breast cancer phenocopy in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is caused by mutations of genes encoding for proteins of the mismatch repair (MMR) machinery. The majority of mutations occur in the MLH1 and MSH2 genes, and consist of splice-site, frameshift and nonsense changes, leading to loss of protein function. In this study, we screened 7 HNPCC families for MLH1/MSH2 mutations. Sequence changes were identified in 5 families. Four alterations were novel 1- or 2-bp deletions or insertions causing a frameshift and appearance of premature stop codons (MLH1: c.597-598delGA, c.1520-1521insT; MSH2: c.1444delA, c.119delG). The four small insertions/ deletions were located within stretches of simple repeated sequences. By reviewing the HNPCC mutation database, we found that the majority of 1-2 bp frameshift mutations similarly affects simple repetitive stretches, pointing to DNA polymerase slippage during replication as the most likely source of such errors. We also evaluated microsatellite instability (MSI) in a breast carcinoma (BC) from an MLH1 mutation carrier. While a colon cancer from the same individual showed MSI, the BC specimen was MSI-negative, indicating that development of the latter tumor was unrelated to MMR impairment, despite presence of a constitutional MLH1 mutation. Hum Mutat 17:521, 2001.     

An appendix carcinoid tumor in a patient with hereditary nonpolyposis colorectal cancer

Gastrointestinal carcinoid tumors are often associated with other tumors, particularly colon adenocarcinomas; but the association between carcinoid tumors and hereditary nonpolyposis colorectal cancer (HNPCC) syndrome has not yet been explored. We report an unusual case of a 28-year-old woman with HNPCC who underwent surgery for a transverse colon adenocarcinoma in whom an appendix carcinoid tumor was incidentally found. To assess whether the carcinoid tumor displayed the characteristic molecular features of HNPCC tumors, we investigated the expression of mismatch-repair (MMR) proteins and microsatellite instability (MSI) status in both tumors. Both tumors demonstrated normal expression of the MMR proteins hMLH1, hMSH2, hMSH6, and hPMS2. Interestingly, the adenocarcinoma exhibited an MSI phenotype but the carcinoid tumor did not, indicating that these 2 tumors arose through different molecular pathways.     

Identification of germline MSH2 gene mutations in endometrial cancer not fulfilling the new clinical criteria for hereditary nonpolyposis colorectal cancer

Endometrial cancer is the second most common malignancy in patients with hereditary nonpolyposis colorectal cancer (HNPCC). This cancer is caused by germline mutations in one of the DNA mismatch repair (MMR) genes. The present study was undertaken to analyze the relation between microsatellite instability (MSI) and germline mutations of MMR genes. We analyzed MSI in 38 cases of endometrial cancer. MSI was present in one or more (out of 5 examined) regions in 11 (29%) cases. Furthermore, alterations in MLH1 and MSH2, two culprit genes representative of HNPCC, were examined in the 11 MSI-positive patients using polymerase chain reaction-single-strand conformation polymorphism and sequencing. Germline mutations, namely, 1) a missense mutation at codon 688 (ATG-->ATA, Met-->Ile) and 2) a missense mutation at codon 390 (CTT-->TTT, Leu-->Phe) of the MSH2 gene, were found in 2 of the 11 patients (18%). Although these two cases do not fulfill the new Amsterdam criteria, they had strong family histories of colorectal and endometrial carcinoma. Our results show that genetic testing is important in cases of endometrial cancer with a history suggestive of HNPCC even if the new Amsterdam criteria are not fulfilled.     

Lymphoepithelioma-like carcinoma of the colon in a patient with hereditary nonpolyposis colorectal cancer.

Tumors with features similar to those of nasopharyngeal carcinoma, so-called lymphoepithelioma-like carcinomas, have been described in several organs but are extremely rare in the colon. We describe a patient with a family history consistent with hereditary nonpolyposis colorectal cancer who had 3 malignant lesions in the right colon, namely, a mucinous cancer, a lymphoepithelioma-like carcinoma, and a well-differentiated adenocarcinoma with prominent lymphoid stroma. To the best of our knowledge, lymphoepithelioma-like carcinoma has not been described previously in hereditary nonpolyposis colorectal cancer.     

Hereditary nonpolyposis colorectal cancer: pitfalls in deletion screening in MSH2 and MLH1 genes

Hereditary nonpolyposis colorectal cancer (HNPCC) is caused by a deficiency in DNA mismatch repair in consequence of germline mutations mainly in the genes MSH2 and MLH1. Around 10% of patients suspected of HNPCC are identified with large genomic deletions that cannot be detected by conventional methods of mutation screening. The recently developed multiplex ligation-dependent probe amplification (MLPA) proved to be an easy to perform method for deletion detection and is reliable when more than one exon is deleted. We show that, in some cases, apparent deletions of single exons may actually result from single base substitutions or small insertions/deletions in the hybridisation sequence of MLPA probes. We conclude that single exon deletions, detected by MLPA or multiplex PCR, should be validated with additional methods.     

两个遗传性非患肉性结直肠癌家系中MLH1和MSH2基因的突变检测

目的 确定两个遗传性非息肉性结直肠癌(hereditary nonpolyposis colorectal cancer,HNPCC)家系的致病基因,选择MLH1基因和MSH2基因进行突变检测.方法 采用聚合酶链反应结合DNA直接测序法,对两个遗传性非息肉性结直肠癌家系的患者进行MLH1基因和MSH2基因的突变检测;发现变异后,采用PCR-限制性片段长度多态性或直接测序法鉴定此变异是否属于突变.结果 在家系A的患者中发现了位于MLH1基因第3外显子内的新突变c.243_244 insA;在家系B的患者中发现了MSH2基因第7外显子内的c.1215_1218dupCCGA突变,这两个突变都导致了编码蛋白的提前终止.结论 MLH1基因的c.243_244insA突变和MSH2基因的c.1215_1218dupCCGA突变分别是导致家系A和家系B发生遗传性非息肉性结直肠癌的致病突变.     

Association of a duodenal follicular lymphoma and hereditary nonpolyposis colorectal cancer.

Hereditary nonpolyposis colorectal cancer (HNPCC) is an inherited predisposition to colorectal and endometrial cancers caused by germline mutation of mismatch repair genes, with hMLH1 and hMSH2 underlying the majority of the cases. Although lymphoid tumors are the most common tumors in mouse models for HNPCC, lymphomas are almost never encountered in patients who have HNPCC, except in rare families with germline homozygous deletion of hMLH1. We report the case of a 53-year-old man who had a history of colon cancers related to constitutional hMLH1 mutation and who was diagnosed as having a duodenal follicular lymphoma This diagnosis was supported by IgH-BCL2 rearrangement and BCL2 immunoreactivity in tumor cells. The association of both of these possibly related rare diseases has never been reported. To clarify this relationship, we searched for hMLH1 expression and mismatch repair deficiency in the duodenal lymphoma. hMLH1 immunostaining was positive in lymphoid tumor cells, and no microsatellite instability was detected. In agreement with mouse models for HNPCC, these results suggest the involvement of alternative mechanisms to complete mismatch repair deficiency for lymphomagenesis in HNPCC syndrome.     

MLH1、MSH2基因 mRNA突变分析与遗传性非息肉性结直肠癌的基因诊断

目的检测胚系MLH1和MSH2基因mRNA突变，确立遗传性非息肉性结直肠癌（hereditary nonpolyposis colorectal cancer，HNPCC）家系。方法收集符合Amsterdam标准Ⅱ的12个家系14名家庭成员外周血，用特异引物和耐热性逆转录酶特异地逆转录MLH1和MSH2的RNA；利用长模板PCR扩增酶扩增逆转录产物（cDNA）；测序分析扩增产物。提取外周血的DNA，设计与利用上述方法检测出突变对应外显子的特异性引物，利用Taq DNA聚合酶扩增测序，以检测上述方法的有效性。结果利用基于外周血mRNA的方法，在6个家系中检出6个胚系突变，4个MLH1突变和2个MSH2突变，MLH1突变分别位于第8、12、16和第19外显子；MSH2突变分别位于第1和第2外显子。利用基于外周血DNA的方法，上述突变均在MLH1和MSH2相应的外显子中得到验证。突变类型为4个错义突变、1个同义突变和1个非编码区突变；其中5个突变国际上尚未报道；6个突变中有5个为病理性，分布于5个不同家系，该5个家系被确诊为HNPCC家系。结论基于外周血MLH1和MSH2 mRNA异常的检测能确诊HNPCC家系；该方法敏感、省时、节约成本。     

中国人遗传性非息肉病性结直肠癌MSH6基因胚系突变的测序研究

目的探讨中国人遗传性非息肉病性结直肠癌(hereditary nonpolyposis colorectal cancer,HNPCC)家系中MSH6基因胚系突变。方法采用PCR-直接测序的方法检测39个无胚系MSH2及MLH1基因突变、符合不同临床标准的中国人HNPCC家系先证者MSH6基因各外显子胚系突变;对137名正常人胚系基因组DNA进行错义突变相应外显子的测序分析。应用Envision二步法检测有突变的先证者肿瘤组织MSH6蛋白表达。结果在39个HNPCC先证者中共发现6个MSH6基因的胚系突变,分别位于第4、6、9和第10外显子;突变类型为4个错义突变、1个无义突变、1个剪接区的插入突变;对4个错义突变的相应外显子的测序分析显示:137名正常人胚系基因组DNA5例具有第6外显子1163密码子处的c.3488A>T的错义突变,约占3.65%(5/137),为单核苷酸多态性(single nucleotide polymorphism,SNP);其余错义突变在正常人群中均未发现。在6例有MSH6基因胚系突变家系的肿瘤组织中免疫组化染色除1例为SNP的肿瘤组织MSH6蛋白阳性表达外,其余均为阴性表达。经过查询国际HNPCC突变数据库及SNP数据库证实上述突变中5个为国际上尚未报道的病理性突变,1个为新发现的SNP。结论MSH6基因胚系突变在符合不同临床标准的中国人HNPCC中均起一定作用,对无MSH2及MLH1基因胚系突变的先证者行MSH6基因胚系突变的测序分析对确诊HNPCC家系是必要的。     

A novel microdeletion syndrome with loss of the MSH2 locus and hereditary non-polyposis colorectal cancer

Constitutional chromosome deletions can predispose to the development of cancer with the phenotypic characteristics of inherited cancer syndromes, when the deleted region encompasses a tumour suppressor gene. Examples of such conditions are represented by the cytogenetic deletions associated with retinoblastoma, Wilms tumour and familial adenomatous polyposis. So far, no constitutional deletions involving the genes implicated in hereditary non-polyposis colorectal cancer (HNPCC) have been identified. This may be at least partially because of the lack of distinctive phenotypic manifestations in HNPCC. We describe the first case of a constitutional microdeletion associated with HNPCC. Suspicion of a microdeletion was prompted by the association of mental retardation, postnatal growth deficiency, minor congenital anomalies and early onset (37 years) sporadic colon cancer. The patient was found to harbour a microdeletion within chromosome 2p16-p21, including the MSH2 gene. Since there are very few reports of deletions of the 2p16-p21 region, our observation sets the grounds for the definition of a novel multiple congenital anomaly/mental retardation/cancer microdeletion syndrome.     

Assessment of pathogenicity criteria for constitutional missense mutations of the hereditary nonpolyposis colorectal cancer genes MLH1 and MSH2

To determine the role played by MLH1 and MSH2 missense variants in cancer susceptibility, we have investigated the following genetic and biological characteristics associated with six MLH1 and four MSH2 missense changes identified in Italian hereditary nonpolyposis colorectal cancer (HNPCC) families: co-segregation with disease phenotype and/or bonafide pathogenetic mutations; presence of the variant in healthy control subjects; evolutionary conservation of the involved aminoacid and type of aminoacid change; and presence/absence of microsatellite instability (MSI) in tumour DNA. Overall, nine variants did not fulfil > or = 2 pathogenicity criteria. MSI was investigated in tumour samples from carriers of nine different missense mutations. Only 3/9 variants were associated with MSI in tumour DNA. In addition, four variants were not present in affected pedigree members, and five variants were observed in the control population. Based upon these results, we conclude that most MLH1 and MSH2 missense changes are unlikely to act as major causative factors in colorectal cancer susceptibility and development.