2956

MSH6

GTBP|HNPCC5|HSAP;mutS homolog 6 (E. coli);MSH6;mutS homolog 6 (E. coli)

DNA mismatch repair protein Msh6|G/T mismatch-binding protein|GTMBP|hMSH6|mutS-alpha 160 kDa subunit|p160|sperm-associated protein

2p16

protein-coding

Hereditary nonpolyposis colorectal cancer (HNPCC) is a cancer-predisposing condition caused by inactivating mutations in at least four genes (MSH2, MLH1, MSH6, and PMS2) belonging to the mismatch repair system. At present, availability of the microsatellite instability (MSI) test allows screening of a relevant fraction of patients with a constellation of features suggestive of HNPCC. By analogy with several other genetic disorders, it is clearly emerging that the term HNPCC encompasses a wide spectrum of different clinical presentations, including Muir-Torre syndrome, Turcot syndrome, and the neurofibromatosis-hematological malignancy association. Notwithstanding the remarkable genetic and allelic heterogeneity, a few consistent phenotype-genotype associations can be recognized. mutations in the MSH2 gene entail higher risks of developing cancer, including extraintestinal ones, than MLH1 alterations. MSH2 also accounts for most cases of Muir-Torre syndrome, which is characterized by the presence of sebaceous skin tumors. The few known PMS2 mutations show a striking association with the presence of gliomas, which are the hallmark of theTurcot variant of HNPCC. Homozygotes for mismatch repair gene mutations present with stigmata of neurofibromatosis 1 and usually die in childhood due to a variety of leukemias and lymphomas. While such correlations are being defined, the underlying reasons have only partially been elucidated, and may include heterogeneous gene functions and properties; types of mutation, some of which may exert dominant negative effects; and genetic and environmental modifiers.#CI- Copyright 2003 Wiley-Liss, Inc.

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant condition due to heterozygous germline mutations in DNA mismatch repair genes, in particular MLH1, MSH2 and MSH6. Recently, a syndrome was recognized in which children develop haematological malignancies, solid tumours and signs of neurofibromatosis type 1 due to bi-allelic MMR gene mutations in MLH1, MSH2 and PMS2. Here we describe the child of healthy consanguineous parents who had cafe-au-lait spots, oligodendroglioma, and rectal cancer. The patient was homozygous for the MSH6 mutation c.3386_3388delGTG in exon 5 which has a predicted pathogenic effect. Germline NF1 gene mutation testing was negative. The rectal tumour showed microsatellite instability and absence of MSH6 staining, whereas the brain tumour was MSI stable and showed normal immunohistochemical expression of MSH6. Apparently, not only MLH1, MSH2 and PMS2, but also MSH6 is involved in the syndrome of childhood cancer and signs of neurofibromatosis type1.

Heterozygous mutations in one of the DNA mismatch repair genes cause hereditary nonpolyposis colorectal cancer (MIM114500). Turcot syndrome (MIM276300) has beendescribed as the association of central nervous system malignant tumors and familial colorectal cancer and has been reported to be both a dominant and recessive disorder. Homozygous and compound heterozygous mutations in APC, MLH1,MSH2, and PMS2 genes have been reported in five families. Here we describe a nonconsanguineous Pakistani family, including a son with lymphoma and colorectalcancer diagnosed at ages 5 and 8, respectively, and an 8-year-old daughter with glioblastoma multiforme. Both children had features of neurofibromatosis type 1 including atypical cafe au lait spots and axillary freckling without a family history consistent with neurofibromatosis type 1, familial adenomatous polyposis, or hereditary nonpolyposis colorectal cancer. mutational analysis was done for MLH1, MSH2, and MSH6 using denaturing high-performance liquid chromatography andsequencing of a blood sample from the daughter. A novel homozygous single base insertion mutation was identified (3634insT) resulting in a premature stop at codon 1,223 in exon 7 of the MSH6 gene. Both parents were found to be heterozygous for the 3634insT mutation. Microsatellite instability testing showed instability in the glioblastoma sample. We report here the first identification of a homozygous mutation in MSH6 in a family with childhood-onset brain tumor, lymphoma, colorectal cancer, and neurofibromatosis type 1 phenotype. Our findings support a role for MSH6 in Turcot syndrome and are consistent with an autosomal recessive mode of inheritance.

Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is caused by heterozygous germline mutations in DNA mismatch repair genes (MMR), (MSH2, MLH1,MSH6, and PMS2) and it is inherited in an autosomal dominant pattern with high penetrance. Several patients have been reported carrying bi-allelic MMR gene mutations and whose phenotype resembled a syndrome with childhood malignancies including hematological malignancies, brain, and colorectal tumors. This phenotype is similar to the tumor spectrum of MMR knockout mice. Herein we describe two brothers of healthy consanguineous parents from Pakistan, who had developed two and three colorectal cancers at the ages of 11 and 12 years, respectively, and less than 30 polyps. tumor specimens were microsatellite instable (MSI-H), and expression of MSH2 and MSH6 was lost. mutation analyses ofDNA samples from both patients revealed a novel homozygous c.2006-5T > A mutation in intron 12 of the MSH2 gene. This phenotype of the brothers is unusual as theyneither develop hematological malignancies nor brain tumors at an older age of presentation than other patients with homozygous MSH2 mutations. The milder phenotype may be due to the expression of low amounts of MSH2 protein with reduced activity.#CI- 2005 Wiley-Liss, Inc.

Heterozygous germline mutations in the human mismatch repair (MMR) genes MLH1, PMS2, MSH2 and MSH6 predispose to the hereditary non-polyposis colorectal cancer(HNPCC) syndrome. Biallelic mutations in these genes have been reported for a limited number of cases resulting in hematological malignancies, brain tumors and gastrointestinal tumors early in childhood. These tumor phenotypes are frequently associated with cafe-au-lait spots (CALS), one of the clinical hallmarks of neurofibromatosis type 1 (NF1). We report the first case of compound heterozygosity for two MSH6 mutations resulting in a nonconservative amino-acid change of a conserved residue and in a premature stop codon in a patient who developed rectal and endometrial cancer at ages 19 and 24 years, respectively, and presented few CALS in a single body segment. Immunohistochemistry and Western blotting revealed only residual expression of the MSH6 protein in the normal cells. The disease history resembles the HNPCC phenotype rather than a phenotypeassociated with biallelic MMR gene mutations. Therefore, we assume that one or both mutations abolish protein function only partially, further supported by theparents, which are both carriers of one of the mutations each, and not affected by the disease at ages 57 and 58 years. Our data suggest considering biallelic mutations in MMR genes for patients who develop HNPCC-associated tumors at an unusually young age of onset, even without hematological or brain malignancies.

Background A 13-year-old girl presented with rectal bleeding and was found to have two colonic carcinomas (stage Dukes' C) and multiple colonic polyps. At theage of 7 years she had widespread hyperpigmented and hypopigmented skin lesions,and had developed medulloblastoma, which was treated with chemotherapy and craniospinal irradiation. At the age of 10 years she had developed acute myelocytic leukemia, M5. She was treated with chemotherapy including sibling bone marrow transplant with busulfan/cyclophosphamide conditioning. A three-generation family history identified no relatives with colonic carcinomas or polyposis. Investigations Immunohistochemical analysis was performed on a sample of colonicadenoma. Staining for MLH1 and MSH2 was normal but was absent for MSH6. Direct sequencing of MSH6 was performed in the proband and both parents. Diagnosis Constitutional biallelic mutations in the mismatch repair gene MSH6 were identified in the proband. Both parents are carriers of one mutation. This is the first individual with biallelic MSH6 mutations reported with either medulloblastoma or acute myelocytic leukemia. Management Cascade genetic testingand colonoscopic screening for colorectal carcinoma has been offered to relatives carrying one mutation. The proband underwent panproctocolectomy and received adjuvant capecitabine. Identification of constitutional biallelic mismatch repair gene mutations allows the avoidance of chemotherapeutic agents likely to be ineffective and mutagenic in the context of the underlying mismatch repair deficiency. It is important to consider this diagnosis in children presenting with malignancy and abnormal skin pigmentation, even in the absence of a strong family history of tumors.

Since the first report by our group in 1999, more than 20 unrelated biallelic mutations in DNA mismatch repair genes (MMR) have been identified. In the present report, we describe two novel cases: one carrying compound heterozygous mutations in the MSH6 gene; and the other, compound heterozygous mutations in the PMS2 gene. Interestingly, the inactivation of one PMS2 allele was likely caused by gene conversion. Although gene conversion has been suggested to be a mutation mechanism underlying PMS2 inactivation, this is the first report of its involvement in a pathogenic mutation. The clinical features of biallelic mutation carriers were similar to other previously described patients, with the presence of cafe-au-lait spots (CALS), early onset of brain tumors, and colorectal neoplasia. Our data provide further evidence of the existence, although rare, ofa distinct recessively inherited syndrome on the basis of MMR constitutional inactivation. The identification of this syndrome should be useful for genetic counseling, especially in families with atypical hereditary nonpolyposis colon cancer (HNPCC) associated with childhood cancers, and for the clinical surveillance of these mutation carriers.#CI- 2007 Wiley-Liss, Inc.

Heterozygous germline mutations in mismatch repair (MMR) genes MLH1, PMS2, MSH2,and MSH6 cause Lynch syndrome. New studies have indicated that biallelic mutations lead to a distinctive syndrome, childhood cancer syndrome (CCS), with haematological malignancies and tumours of brain and bowel early in childhood, often associated with signs of neurofibromatosis type 1. We provide further evidence for CCS reporting on six children from two consanguineous families carrying homozygous PMS2 germline mutations. In family 1, ALL four children had the homozygous p.I590Xfs mutation. Two had a glioblastoma at the age of 6 years and one of them had three additional Lynch-syndrome associated tumours at 15. Another sibling suffered from a glioblastoma at age 9, and the fourth sibling had infantile myofibromatosis at 1. In family 2, two of four siblings were homozygous for the p.G271V mutation. One had two colorectal cancers diagnosed at ages 13 and 14, the other had a Non-Hodgkin's lymphoma and a colorectal cancer at ages 10 and 11, respectively. ALL children with malignancies had multiple cafe-au-lait spots. After reviewing published cases of biallelic MMR gene mutations, we provide a concise description of CCS, revealing similarities in age distribution with carriers of heterozygous MMR gene mutations.

Heterozygous germline mutations in one of the mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2 cause hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome, a dominantly inherited cancer susceptibility syndrome. Recent reports provide evidence for a novel recessively inherited cancer syndrome with constitutive MMR deficiency due to biallelic germline mutations in one of the MMR genes. MMR-deficiency (MMR-D) syndrome is characterized by childhood brain tumors, hematological and/or gastrointestinal malignancies, and signs of neurofibromatosis type 1 (NF1). We established an RNA-based mutation detection assay for the four MMR genes, since 1) a number of splicing defects may escape detection by the analysis of genomic DNA, and 2) DNA-based mutation detection inthe PMS2 gene is severely hampered by the presence of multiple highly similar pseudogenes, including PMS2CL. Using this assay, which is based on direct cDNA sequencing of RT-PCR products, we investigated two families with children suspected to suffer from MMR-D syndrome. We identified a homozygous complex MSH6splicing alteration in the index patients of the first family and a novel homozygous PMS2 mutation (c.182delA) in the index patient of the second family. Furthermore, we demonstrate, by the analysis of a PMS2/PMS2CL "hybrid" allele carrier, that RNA-based PMS2 testing effectively avoids the caveats of genomic DNA amplification approaches; i.e., pseudogene coamplification as well as allelic dropout, and will, thus, allow more sensitive mutation analysis in MMR deficiency and in HNPCC patients with PMS2 defects.#CI- (c) 2007 Wiley-Liss, Inc.

Mono-allelic germline mutations in mismatch repair (MMR) genes lead to Lynch syndrome, an autosomal dominant syndrome with an increased risk of predominantlycolorectal and endometrial cancers. Bi-allelic germline mutations in MMR genes predispose to haematological malignancies, brain tumours, gastrointestinal tumours, polyposis and features of neurofibromatosis type 1 in early childhood.We report a brother and a sister with bi-allelic germline mutations in MSH2; a pathogenic deletion of the first 6 exons and a variant of the initiation codon (c.1A>G (p.Met1?)), whereas their phenotypes (four colorectal cancers, small bowel carcinoma and 15 adenomas at age 39 and 48, and colorectal cancer, endometrial cancer and four adenomas at age 33 and 44, respectively) are more suggestive of a mono-allelic pathogenic MMR gene mutation. The carcinomas showedmicrosatellite instability in the presence of MLH1, PMS2, MSH2 and MSH6 proteins, indicating that the variant c.1A>G leads to an alternative protein with reduced activity that is retained in the tumours.Our data suggest that the MSH2 variant c.1A>G (p.Met1?) should not be considered as a regular pathogenic mutation that leads to a strongly increased cancer risk, though it possibly contributes to a more severe phenotype when combined with a truncating mutation on the other allele.

An 8-year-old male with lymphoblastic lymphoma was noted to have multiple cafe-au-lait macules and possible Lisch nodules. Work-up revealed the child as compound heterozygous for mutations in the DNA mismatch repair gene, MSH6. This case emphasizes many clinical issues regarding individuals with biallelic mismatch repair mutations, a rare and easily missed hereditary predisposition tochildhood cancer. The issues include the need for high clinical suspicion based on skin examination findings and family history, the phenotypic similarity to neurofibromatosis type 1 with possibility of misdiagnosis, the high risk for subsequent malignances, and the need for further research of possible treatment resistance.

OBJECTIVES: A novel cancer syndrome associated with biallelic mismatch repair (MMR) mutations has been described recently. Patients presenting with childhood-onset gastrointestinal (GI) cancers may carry biallelic MMR mutations and have a distinct phenotype from classic Lynch syndrome. The aim of this studywas to characterize patients with GI small bowel and/or colorectal cancers (CRCs) who have germline biallelic MMR mutations. METHODS: A search of a Canadian GI cancer registry and literature review to identify patients with biallelic MMR was conducted. RESULTS: The database identified 237 patients with intestinal cancer diagnosed before the age of 35 years. Five (2.1%) patients had biallelic MMR mutations. Overall, 32 individuals, from 29 families, with biallelic MMR gene mutations and GI cancers were identified by the registry and literature review. Among the 29 patients with CRCs, the mean age of first cancer diagnosis was 16.4years (range: 5-28). More than one-third of patients had multiple colorectal adenomas (>10 polyps). Six individuals with biallelic MMR gene mutations have been reported with small bowel adenocarcinoma (mean age 20 years (range: 11-41)). Cafe-au-lait (CAL) macules were reported in 72% and, based on mutation analysis,consanguinity was suspected in 52% of kindred. Of the 29 kindred, 19 (66%) had PMS2 mutations, 6 (21%) had MSH6 mutations, 3 (10%) had MLH1 mutations, and 1 (3%) had MSH2 mutation. CONCLUSIONS: Biallelic MMR mutations are an underrecognized cause of small bowel and colonic cancers in children and young adults. This distinct phenotype includes multiple adenomatous polyps and CAL skin lesions. It is important to identify such patients, so that families can be referred for genetic testing and counseling.

High grade gliomas (HGG) are one of the leading causes of cancer-related deaths in children, and there is increasing evidence that pediatric HGG may harbor distinct molecular characteristics compared to adult tumors. We have sought to clarify the role of microsatellite instability (MSI) in pediatric versus adult HGG. MSI status was determined in 144 patients (71 pediatric and 73 adults) using a well established panel of five quasimonomorphic mononucleotide repeat markers.expression of MLH1, MSH2, MSH6 and PMS2 was determined by immunohistochemistry, MLH1 was assessed for mutations by direct sequencing and promoter methylation using MS-PCR. DNA copy number profiles were derived using array CGH, and mutations in eighteen MSI target genes studied by multiplex PCR and genotyping. MSI was found in 14/71 (19.7%) pediatric cases, significantly more than observedin adults (5/73, 6.8%; p = 0.02, Chi-square test). MLH1 expression was downregulated in 10/13 cases, however no mutations or promoter methylation were found. MSH6 was absent in one pediatric MSI-High tumor, consistent with an inherited mismatch repair deficiency associated with germline MSH6 mutation. MSIwas classed as Type A, and associated with a remarkably stable genomic profile. Of the eighteen classic MSI target genes, we identified mutations only in MSH6 and DNAPKcs and described a polymorphism in MRE11 without apparent functional consequences in DNA double strand break detection and repair. This study thus provides evidence for a potential novel molecular pathway in a proportion of gliomas associated with the presence of MSI.

INTRODUCTION: JC virus (JCV) may infect the gastrointestinal tract in childhood,and, by encoding a gene for T-antigen (T Ag), can initiate chromosomal instability in epithelial cells. AIM: We looked for JCV DNA in the cancer tissueof patients with sporadic colorectal cancer (CRC, Group A) and with positive family history and Bethesda criteria (Group B). We hypothesized that the role ofJCV may be different between these two groups. METHODS: Fifty-six patients were randomly selected from our database, 30 in Group A and 26 in Group B. DNA was isolated from the tumor, normal mucosa, and plasma, and JCV DNA sequences were looked for with specific polymerase chain reaction (PCR) assays for T Ag primers. Immunohistochemistry for hMLH1, hMSH2, hMSH6, and PMS2 was performed on paraffin-embedded tissue. RESULTS: In Group A, T Ag was demonstrated in 6 (20.00%) and 3 (10.00%) of the tumors and adjacent normal mucosa, respectively (P = 0.094). In Group B, the corresponding observations were 10 (38.46%) and 6 (23.07%), respectively (P < 0.001). Immunohistochemistry for hMLH1, hMSH2, hMSH6, and PMS2 was performed in ALL of the Group A and B patients. ALL patients of Group A (100%) showed expression of these proteins, while only 19 patients of Group B did so (73.1%), P = 0.009. JCV T Ag DNA was found in 20, 28.5, and 42.1%of the tumors in Group A, Group B with negative staining for DNA repair genes, and Group B with a positive staining, respectively (NS). CONCLUSION: CRC patients with positive family history have a higher incidence of JCV T Ag, but this did not correlate with specific DNA repair gene mutations. We could not conclude that, on the background of genetic mutation in one of the DNA repair genes, JCV acts as the missing link in the chain of events leading to CRC.

Colorectal adenocarcinoma (CRAC) is exceedingly rare in the pediatric population(fewer than 2 cases per 1 million children). There are 2 major categories of pediatric colorectal adenocarcinoma syndromes: polyposis-related and hereditary nonpolyposis colorectal cancer, also known as Lynch syndrome. Germ line mutations in DNA mismatch repair (MMR) genes (eg, MLH1, MSH2, PMS2, MSH6) have been established as the molecular genetic basis of Lynch syndrome. Another prognosticfactor in adult CRAC is the reduced expression of epithelial cadherin (E-cadherin), which has been associated with poor outcome in some adult CRAC cases; however, its role in predicting prognoses in pediatric cases remains unclear. Seven pediatric patients with primary CRAC were reviewed. Available molecular genetic test results were evaluated, and immunohistochemical labeling for MMR proteins and E-cadherin were performed on 5 patients. Four of the 5 patients in our study with available paraffin blocks showed loss of MMR protein expression, consistent with Lynch syndrome. In cases stained for E-cadherin, 3 were strongly positive and 2 were weakly positive; however, with the small sample size and the relatively short follow-up period, an accurate correlation between E-cadherin and prognosis cannot be reached with any degree of certainty. Our findings highlight the importance of genetic testing for MMR gene mutations in children with colorectal cancer and suggest further investigation into the prognostic role of E-cadherin in pediatric CRAC.