Claire Groombridge

Colorectal cancer susceptibility loci on chromosome 8q23.3 and 11q23.1 as modifiers for disease expression in lynch syndrome

Objective Recently, six colorectal cancer (CRC) susceptibility loci have been identified, and two single-nucleotide polymorphisms (SNPs)—rs16892766 (8q23.3) and rs3802842 (11q23.1)—from two of these regions have been found to be significantly associated with an increased CRC risk in patients with Lynch syndrome. The objective of this study was to genotype nine SNPs within these six loci to confirm previous findings and investigate whether they act as modifiers of disease risk in patients with Lynch syndrome. Design The patient cohort consisted of 684 mutation-positive patients with Lynch syndrome from 298 Australian and Polish families. Nine SNPs were genotyped: rs16892766 (8q23.3), rs7014346 and rs6983267 (8q24.21), rs10795668 (10p14), rs3802842 (11q23.1), rs10318 and rs4779584 (15q13.3), and rs4939827 and rs4464148 (18q21.1). The data were analysed to investigate possible associations between the presence of variant alleles and the risk of developing disease. Results An association between SNP rs3802842 on chromosome 11q23.1 and rs16892766 on chromosome 8q23.3 and the risk of developing CRC and age of diagnosis was found in MLH1 mutation carriers. Female MLH1 mutation carriers harbouring the homozygous variant genotype for SNP rs3802842 have the highest risk of developing CRC. When the number of risk alleles for the two SNPs combined was analysed, a difference of 24 years was detected between individuals carrying three risk alleles and those carrying no risk alleles. Conclusion The authors were able to replicate the association between the CRC susceptibility loci on chromosomes 8q23.3 and 11q23 and the risk of developing CRC in patients with Lynch syndrome, but the association could only be detected in MLH1 mutation carriers in this study.

Mutation analysis of the MYH gene in an Australian series of colorectal polyposis patients with or without germline APC mutations

The MYH gene has recently been shown to be associated with a recessive form of colorectal adenomatous polyposis. Two common mutations in the MYH gene have been identified that lend themselves to rapid screening. We have examined a series of 302 individuals comprising 120 control subjects, 120 patients diagnosed with adenomatous polyposis but without germline mutations in the APC gene and 62 patients diagnosed with familial adenomatous polyposis all harbouring confirmed causative APC germline mutations. The results reveal that MYH accounts for 16 percent of polyposis patients without germline mutations in the APC gene and that it does not appear to be a modifier gene in FAP patients diagnosed with APC germline mutations.

Haemochromatosis HFE gene polymorphisms as potential modifiers of hereditary nonpolyposis colorectal cancer risk and onset age

Hereditary nonpolyposis colorectal cancer (HNPCC) is characterized by germline mutations in DNA mismatch repair genes; however, variation in disease expression suggests that there are potential modifying factors. Polymorphisms of the HFE gene, which cause the iron overload disorder hereditary haemochromatosis, have been proposed as potential risk factors for the development of colorectal cancer (CRC). To understand the relationship between HNPCC disease phenotype and polymorphisms of the HFE gene, a total of 362 individuals from Australia and Poland with confirmed causative MMR gene mutations were genotyped for the HFE C282Y and H63D polymorphisms. A significantly increased risk of developing CRC was observed for H63D homozygotes when compared with combined wild‐type homozygotes and heterozygotes (hazard ratio = 2.93, p = 0.007). Evidence for earlier CRC onset was also observed in H63D homozygotes with a median age of onset 6 years earlier than wild type or heterozygous participants (44 vs. 50 years of age). This effect was significant by all tests used (log‐rank test p = 0.026, Wilcoxon p = 0.044, Tarone‐Ware p = 0.035). No association was identified for heterozygosity of either polymorphism and limitations on power‐prevented investigation of C282Y homozygosity or compound C282Y/H63D heterozygosity. In the Australian sample only, women had a significantly reduced risk of developing CRC when compared with men (hazard ratio = 0.58, p = 0.012) independent of HFE genotype for either single nucleotide polymorphisms. In conclusion, homozygosity for the HFE H63D polymorphism seems to be a genetic modifier of disease expression in HNPCC. Understanding the mechanisms by which HFE interrelates with colorectal malignancies could lead to reduction of disease risk in HNPCC.

Impact of microsatellite testing and mismatch repair protein expression on the clinical interpretation of genetic testing in hereditary non-polyposis colorectal cancer

Abstract Purpose. Identification of germline mutations in mismatch repair genes is increasingly being used to guide clinical practice in hereditary non-polyposis colon cancer. The aim of this study was to retrospectively assess the clinical utility of immunostaining and microsatellite instability testing in a group of individuals in whom germline testing of hMSH2 and hMLH1 had already been performed. Methods. Individuals were identified from the records of family cancer clinics. A total of thirty-eight tumour blocks were retrieved from 28 kindreds. DNA was extracted and PCR amplification of six microsatellite markers was performed. Immunostaining was used to examine the expression of hMSH2 and hMLH1 protein. Results. Of the 32 assessable tumours, 24 (75%) showed microsatellite instability. Most of the MSI-H cancers (92%) failed to express either hMLH1 or hMSH2. Deleterious germline mutations were identified in the proband in 12 of 28 families. Missense mutations were identified in 11 cases and no mutations in six probands. Conclusions. The use of germline genetic testing is indicated for a highly selected group of individuals. MSI testing and immunostaining are extremely useful tools which significantly improve the clinical interpretation of germline results. Ambiguity regarding the significance of missense mutations in hereditary bowel cancer suggests that these findings should be interpreted with caution.

MSH6 and PMS2 mutation positive Australian Lynch syndrome families: novel mutations, cancer risk and age of diagnosis of colorectal cancer

BackgroundApproximately 10% of Lynch syndrome families have a mutation in MSH6 and fewer families have a mutation in PMS2. It is assumed that the cancer incidence is the same in families with mutations in MSH6 as in families with mutations in MLH1/MSH2 but that the disease tends to occur later in life, little is known about families with PMS2 mutations. This study reports on our findings on mutation type, cancer risk and age of diagnosis in MSH6 and PMS2 families.MethodsA total of 78 participants (from 29 families) with a mutation in MSH6 and 7 participants (from 6 families) with a mutation in PMS2 were included in the current study. A database of de-identified patient information was analysed to extract all relevant information such as mutation type, cancer incidence, age of diagnosis and cancer type in this Lynch syndrome cohort. Cumulative lifetime risk was calculated utilising Kaplan-Meier survival analysis.ResultsMSH6 and PMS2 mutations represent 10.3% and 1.9%, respectively, of the pathogenic mutations in our Australian Lynch syndrome families. We identified 26 different MSH6 and 4 different PMS2 mutations in the 35 families studied. We report 15 novel MSH6 and 1 novel PMS2 mutations. The estimated cumulative risk of CRC at age 70 years was 61% (similar in males and females) and 65% for endometrial cancer in MSH6 mutation carriers. The risk of developing CRC is different between males and females at age 50 years, which is 34% for males and 21% for females.ConclusionNovel MSH6 and PMS2 mutations are being reported and submitted to the current databases for identified Lynch syndrome mutations. Our data provides additional information to add to the genotype-phenotype spectrum for both MSH6 and PMS2 mutations.

Combined analysis of three lynch syndrome cohorts confirms the modifying effects of 8q23.3 and 11q23.1 in MLH1 mutation carriers

Two colorectal cancer (CRC) susceptibility loci have been found to be significantly associated with an increased risk of CRC in Dutch Lynch syndrome (LS) patients. Recently, in a combined study of Australian and Polish LS patients, only MLH1 mutation carriers were found to be at increased risk of disease. A combined analysis of the three data‐sets was performed to better define this association. This cohort‐study includes three sample populations combined totaling 1,352 individuals from 424 families with a molecular diagnosis of LS. Seven SNPs, from six different CRC susceptibility loci, were genotyped by both research groups and the data analyzed collectively. We identified associations at two of the six CRC susceptibility loci in MLH1 mutation carriers from the combined LS cohort: 11q23.1 (rs3802842, HR = 2.68, p ≤ 0.0001) increasing risk of CRC, and rs3802842 in a pair‐wise combination with 8q23.3 (rs16892766) affecting age of diagnosis of CRC (log‐rank test; p ≤ 0.0001). A significant difference in the age of diagnosis of CRC of 28 years was observed in individuals carrying three risk alleles compared to those with 0 risk alleles for the pair‐wise SNP combination. A trend (due to significance threshold of p ≤ 0.0010) was observed in MLH1 mutation carriers towards an increased risk of CRC for the pair‐wise combination (p = 0.002). This study confirms the role of modifier loci in LS. We consider that LS patients with MLH1 mutations would greatly benefit from additional genotyping of SNPs rs3802842 and rs16892766 for personalized risk assessment and a tailored surveillance program.

DNA repair gene polymorphisms and risk of early onset colorectal cancer in Lynch syndrome

DNA repair plays a pivotal role in maintaining genomic integrity with over 130 genes involved in various repair pathways that include base excision repair, nucleotide excision repair, double strand break repair and DNA mismatch repair. Polymorphisms within genes that are involved in these processes have been widely reported to be associated with cancer susceptibility in an extensive range of malignancies that include colorectal cancer (CRC). Lynch syndrome is caused by inherited germline mutations in DNA mismatch repair genes, predominantly in MLH1 and MSH2, that predispose to a variety of epithelial malignancies, most notably CRC. Despite being a relatively well understood hereditary cancer syndrome there remain several questions in relation to genetic influences on disease expression. Since Lynch syndrome is associated with a breakdown in DNA mismatch repair variation in other DNA repair genes may influence disease expression. In this report we have genotyped 424 Australian and Polish Lynch syndrome participants for eight common DNA repair gene polymorphisms to assess any association with the age of CRC onset. The DNA repair gene SNPs included in the study were: BRCA2 (rs11571653), MSH3 (rs26279), Lig4 (rs1805386), OGG1 (rs1052133), XRCC1 (rs25487), XRCC2 (rs3218536 and rs1799793) and XRCC3 (rs861539). Cox multi-variant regression modelling failed to provide any convincing evidence of an effect in any of the polymorphisms analysed. The data suggest that polymorphisms in DNA repair genes do not contribute to cancer risk in a population of CRC patients who are at increased risk of disease as a result in a deficiency of DNA mismatch repair.

MTHFR 677 C>T and 1298 A>C polymorphisms and the age of onset of colorectal cancer in hereditary nonpolyposis colorectal cancer

Hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome is characterized by inactivating germline mutations in DNA mismatch repair genes resulting in an increased risk of developing an epithelial malignancy. There is considerable variability in disease expression observed in this syndrome, which is thought to be due to a combination of genetic and environmental factors. Alterations in the kinetics of methylene tetrahydrofolate reductase (MTHFR) due to the presence of polymorphisms in the MTHFR gene have been associated with an increased risk of colorectal cancer (CRC). Two common single nucleotide polymorphisms (SNPs) located within the MTHFR gene, 677 C>T and 1298 A>C, that alter the function of the encoded protein have been the focus of many studies on CRC risk outside the context of an inherited predisposition to disease. In this report, a total of 417 HNPCC participants were genotyped for the 677 C>T and 1298 A>C SNPs to determine whether there exists an association with the age of disease onset of CRC. Genotyping of both SNPs was performed by TaqMan® assay technology. Associations in disease risk were further investigated using Kaplan–Meier survival analysis and Cox hazard regression. The average ages of disease diagnosis were found to be different between individuals harbouring either one of the MTHFR polymorphisms. Both Kaplan–Meier and Cox hazard regression analyses revealed a more complex relationship between the two polymorphisms and the age of CRC onset. The Kaplan–Meier survival analysis revealed that compound heterozygotes for the two SNPs developed CRC 10 years later compared with those carrying only wild-type alleles.

Psychosocial Impact of Familial Adenomatous Polyposis on Young Adults: A Qualitative Study

The aim of this study was to explore in detail the psychosocial impact of either having familial adenomatous polyposis (FAP) or being at risk for FAP amongst young adults. In-depth interviews were conducted with eleven individuals aged 18–35 with a clinical or genetic diagnosis of, or at risk of developing FAP. While being at risk did not seem to have a major psychosocial impact upon clinically unaffected participants, clinically affected individuals discussed a number of major stressors including issues in relation to changes in body image and physical functioning as a result of surgery, concerns about discussing FAP with new partners, difficulties in relation to childbearing decision-making, and impact on employment. Genetic counseling was described as being highly effective in providing support, but most participants were not aware of any other support services. Providing longer-term support through ongoing genetic counseling appears necessary to adequately address the ongoing challenges faced by young adults who are dealing with FAP.

Can a familial gastrointestinal tumour syndrome be allelic with Waardenburg syndrome

Vilain RE, Dudding T, Braye SG, Groombridge C, Meldrum C, Spigelman AD, Ackland S, Ashman L, Scott RJ. Can a familial gastrointestinal tumour syndrome be allelic with Waardenburg syndrome?