MutYH (MYH) and colorectal cancer

Antioxidant enzyme and DNA base repair genetic risk scores' associations with systemic oxidative stress biomarker in pooled cross-sectional studies

Background: Oxidative stress is hypothesized to contribute to the pathogenesis of several chronic diseases. Numerous dietary and lifestyle factors are associated with oxidative stress; however, little is known about associations of genetic factors, individually or jointly with dietary and lifestyle factors, with oxidative stress in humans. Methods: We genotyped 22 haplotype-tagging single nucleotide polymorphisms (SNPs) in 3 antioxidant enzyme (AE) genes and 79 SNPs in 14 DNA base excision repair (BER) genes to develop oxidative stress-specific AE and BER genetic risk scores (GRS) in two pooled cross-sectional studies (n = 245) of 30-74-year-old, White, cancer- and inflammatory bowel disease-free adults. Of the genotypes, based on their associations with a systemic oxidative stress biomarker, plasma F₂-isoprostanes (FiP) concentrations, we selected 4 GSTP1 SNPs for an AE GRS, and 12 SNPs of 5 genes (XRCC1, TDG, PNKP, MUTYH, and FEN1) for a BER GRS. We also calculated a previously-reported, validated, questionnaire-based, oxidative stress biomarker-weighted oxidative balance score (OBS) comprising 17 anti- and pro-oxidant dietary and lifestyle exposures, with higher scores representing a higher predominance of antioxidant exposures. We used general linear regression to assess adjusted mean FiP concentrations across GRS and OBS tertiles, separately and jointly. Results: The adjusted mean FiP concentrations among those in the highest relative to the lowest oxidative stress-specific AE and BER GRS tertiles were, proportionately, 11.8% (p = 0.12) and 21.2% (p = 0.002) higher, respectively. In the joint AE/BER GRS analysis, the highest estimated mean FiP concentration was among those with jointly high AE/BER GRS. Mean FiP concentrations across OBS tertiles were similar across AE and BER GRS strata. Conclusion: Our pilot study findings suggest that DNA BER, and possibly AE, genotypes collectively may be associated with systemic oxidative stress in humans, and support further research in larger, general populations.

Inherited MUTYH mutations cause elevated somatic mutation rates and distinctive mutational signatures in normal human cells

Cellular DNA damage caused by reactive oxygen species is repaired by the base excision repair (BER) pathway which includes the DNA glycosylase MUTYH. Inherited biallelic MUTYH mutations cause predisposition to colorectal adenomas and carcinoma. However, the mechanistic progression from germline MUTYH mutations to MUTYH-Associated Polyposis (MAP) is incompletely understood. Here, we sequence normal tissue DNAs from 10 individuals with MAP. Somatic base substitution mutation rates in intestinal epithelial cells were elevated 2 to 4-fold in all individuals, except for one showing a 31-fold increase, and were also increased in other tissues. The increased mutation burdens were of multiple mutational signatures characterised by C > A changes. Different mutation rates and signatures between individuals are likely due to different MUTYH mutations or additional inherited mutations in other BER pathway genes. The elevated base substitution rate in normal cells likely accounts for the predisposition to neoplasia in MAP. Despite ubiquitously elevated mutation rates, individuals with MAP do not display overt evidence of premature ageing. Thus, accumulation of somatic mutations may not be sufficient to cause the global organismal functional decline of ageing.

Associations of DNA Base Excision Repair and Antioxidant Enzyme Genetic Risk Scores with Biomarker of Systemic Inflammation

Background: Inflammation is implicated in the etiology of various aging-related diseases. Numerous dietary and lifestyle factors contribute to chronic systemic inflammation; genetic variation may too. However, despite biological plausibility, little is known about associations of antioxidant enzyme (AE) and DNA base excision repair (BER) genotypes with human systemic inflammation. Methods: We genotyped 22 single nucleotide polymorphisms (SNPs) in 3 AE genes, and 79 SNPs in 14 BER genes to develop inflammation-specific AE and BER genetic risk scores (GRS) in two pooled cross-sectional studies (n = 333) of 30-74-year-old White adults without inflammatory bowel disease, familial adenomatous polyposis, or a history of cancer or colorectal adenoma. Of the genotypes, based on their associations with a biomarker of systemic inflammation, circulating high sensitivity C-reactive protein (hsCRP) concentrations, we selected 2 SNPs of 2 genes (CAT and MnSoD) for an AE GRS, and 7 SNPs of 5 genes (MUTYH, SMUG1, TDG, UNG, and XRCC1) for a BER GRS. A higher GRS indicates a higher balance of variant alleles directly associated with hsCRP relative to variant alleles inversely associated with hsCRP. We also calculated previously-reported, validated, questionnaire-based dietary (DIS) and lifestyle (LIS) inflammation scores. We used multivariable general linear regression to compare mean hsCRP concentrations across AE and BER GRS categories, individually and jointly with the DIS and LIS. Results: The mean hsCRP concentrations among those in the highest relative to the lowest AE and BER GRS categories were, proportionately, 13.9% (p = 0.30) and 57.4% (p = 0.009) higher. Neither GRS clearly appeared to modify the associations of the DIS or LIS with hsCRP. Conclusion: Our findings suggest that genotypes of DNA BER genes collectively may be associated with systemic inflammation in humans.

Selection shapes the landscape of functional variation in wild house mice

BACKGROUND

Through human-aided dispersal over the last ~ 10,000 years, house mice (Mus musculus) have recently colonized diverse habitats across the globe, promoting the emergence of new traits that confer adaptive advantages in distinct environments. Despite their status as the premier mammalian model system, the impact of this demographic and selective history on the global patterning of disease-relevant trait variation in wild mouse populations is poorly understood.

RESULTS

Here, we leveraged 154 whole-genome sequences from diverse wild house mouse populations to survey the geographic organization of functional variation and systematically identify signals of positive selection. We show that a significant proportion of wild mouse variation is private to single populations, including numerous predicted functional alleles. In addition, we report strong signals of positive selection at many genes associated with both complex and Mendelian diseases in humans. Notably, we detect a significant excess of selection signals at disease-associated genes relative to null expectations, pointing to the important role of adaptation in shaping the landscape of functional variation in wild mouse populations. We also uncover strong signals of selection at multiple genes involved in starch digestion, including Mgam and Amy1. We speculate that the successful emergence of the human-mouse commensalism may have been facilitated, in part, by dietary adaptations at these loci. Finally, our work uncovers multiple cryptic structural variants that manifest as putative signals of positive selection, highlighting an important and under-appreciated source of false-positive signals in genome-wide selection scans.

CONCLUSIONS

Overall, our findings highlight the role of adaptation in shaping wild mouse genetic variation at human disease-associated genes. Our work also highlights the biomedical relevance of wild mouse genetic diversity and underscores the potential for targeted sampling of mice from specific populations as a strategy for developing effective new mouse models of both rare and common human diseases.

The double-edged sword of cancer mutations: exploiting neoepitopes for the fight against cancer

Defects in DNA repair have been linked to the accumulation of somatic mutations in tumours. These mutations can promote oncogenesis; however, recent developments have indicated that they may also lead to a targeted immune response against the tumour. This response is initiated by the development of new antigenic epitopes (neoepitopes) arising from mutations in protein-coding genes that are processed and then presented on the surface of tumour cells. These neoepitopes are unique to the tumour, thus enabling lymphocytes to launch an immune response against the cancer cells. Immunotherapies, such as checkpoint inhibitors (CPIs) and tumour-derived vaccines, have been shown to enhance the immunogenic response to cancers and have led to complete remission in some cancer patients. There are tumours that are not responsive to immunotherapy or conventional tumour therapeutics; therefore, there is a push for new treatments to combat these unresponsive cancers. Recently, combinatorial treatments have been developed to further utilise the immune system in the fight against cancer. These treatments have the potential to exploit the defects in DNA repair by inducing more DNA damage and mutations. This can potentially lead to the expression of high levels of neoepitopes on the surface of tumour cells that will stimulate an immunological response. Overall, exploiting DNA repair defects in tumours may provide an edge in this long fight against cancer.

Genomic and transcriptomic profiling of carcinogenesis in patients with familial adenomatous polyposis

OBJECTIVE

Familial adenomatous polyposis (FAP) is characterised by the development of hundreds to thousands of adenomas at different evolutionary stages in the colon and rectum that will inevitably progress to adenocarcinomas if left untreated. Here, we investigated the genetic alterations and transcriptomic transitions from precancerous adenoma to carcinoma.

DESIGN

Whole-exome sequencing, whole-genome sequencing and single-cell RNA sequencing were performed on matched adjacent normal tissues, multiregionally sampled adenomas at different stages and carcinomas from six patients with FAP and one patient with MUTYH-associated polyposis (n=56 exomes, n=56 genomes and n=8,757 single cells). Genomic alterations (including copy number alterations and somatic mutations), clonal architectures and transcriptome dynamics during adenocarcinoma carcinogenesis were comprehensively investigated.

RESULTS

Genomic evolutionary analysis showed that adjacent lesions from the same patient with FAP can originate from the same cancer-primed cell. In addition, the tricarboxylic acid cycle pathway was strongly repressed in adenomas and was then slightly alleviated in carcinomas. Cells from the 'normal' colon epithelium of patients with FAP already showed metabolic reprogramming compared with cells from the normal colon epithelium of patients with sporadic colorectal cancer.

CONCLUSIONS

The process described in the previously reported field cancerisation model also occurs in patients with FAP and can contribute to the formation of adjacent lesions in patients with FAP. Reprogramming of carbohydrate metabolism has already occurred at the precancerous adenoma stage. Our study provides an accurate picture of the genomic and transcriptomic landscapes during the initiation and progression of carcinogenesis, especially during the transition from adenoma to carcinoma.

Attenuated familial adenomatous polyposis (AFAP) in a patient associated with a novel mutation in APC

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome associated with mutation in the adenomatous polyposis coli (APC) gene, a tumour suppressor located on chromosome 5q21. Attenuated familial adenomatous polyposis (AFAP) is a variant associated with fewer and later onset of colon polyps. AFAP-associated APC mutations have largely been found before codon 157, in exon 9 or after codon 1595. We present the case of a 44-year-old man incidentally found to have numerous gastric polyps during bariatric surgery, with innumerable polyps in the remaining part of the stomach and the entire colon, with rectal sparing, consistent with AFAP phenotype. Genetic testing demonstrated the c.7682dup (p.Ser2562Lysfs*21) variant in exon 15 of APC. This represents a previously undescribed APC mutation. This mutation likely yields end-binding protein 1 and human disc large binding protein inactivation, causing cell cycle microtubule dysregulation and tumour suppressor inactivation. Through loss of these regulatory mechanisms, this mutation is associated with AFAP phenotype. The patient was treated surgically and is doing well.

Single molecule glycosylase studies with engineered 8-oxoguanine DNA damage sites show functional defects of a MUTYH polyposis variant

Proper repair of oxidatively damaged DNA bases is essential to maintain genome stability. 8-Oxoguanine (7,8-dihydro-8-oxoguanine, 8-oxoG) is a dangerous DNA lesion because it can mispair with adenine (A) during replication resulting in guanine to thymine transversion mutations. MUTYH DNA glycosylase is responsible for recognizing and removing the adenine from 8-oxoG:adenine (8-oxoG:A) sites. Biallelic mutations in the MUTYH gene predispose individuals to MUTYH-associated polyposis (MAP), and the most commonly observed mutation in some MAP populations is Y165C. Tyr165 is a ‘wedge’ residue that intercalates into the DNA duplex in the lesion bound state. Here, we utilize single molecule fluorescence microscopy to visualize the real-time search behavior of Escherichia coli and Mus musculus MUTYH WT and wedge variant orthologs on DNA tightropes that contain 8-oxoG:A, 8-oxoG:cytosine, or apurinic product analog sites. We observe that MUTYH WT is able to efficiently find 8-oxoG:A damage and form highly stable bound complexes. In contrast, MUTYH Y150C shows decreased binding lifetimes on undamaged DNA and fails to form a stable lesion recognition complex at damage sites. These findings suggest that MUTYH does not rely upon the wedge residue for damage site recognition, but this residue stabilizes the lesion recognition complex.

Portrait of a cancer: mutational signature analyses for cancer diagnostics

BACKGROUND

In the past decade, systematic and comprehensive analyses of cancer genomes have identified cancer driver genes and revealed unprecedented insight into the molecular mechanisms underlying the initiation and progression of cancer. These studies illustrate that although every cancer has a unique genetic make-up, there are only a limited number of mechanisms that shape the mutational landscapes of cancer genomes, as reflected by characteristic computationally-derived mutational signatures. Importantly, the molecular mechanisms underlying specific signatures can now be dissected and coupled to treatment strategies. Systematic characterization of mutational signatures in a cancer patient's genome may thus be a promising new tool for molecular tumor diagnosis and classification.

RESULTS

In this review, we describe the status of mutational signature analysis in cancer genomes and discuss the opportunities and relevance, as well as future challenges, for further implementation of mutational signatures in clinical tumor diagnostics and therapy guidance.

CONCLUSIONS

Scientific studies have illustrated the potential of mutational signature analysis in cancer research. As such, we believe that the implementation of mutational signature analysis within the diagnostic workflow will improve cancer diagnosis in the future.

Endoscopic Phenotype of Monoallelic Carriers of MUTYH Gene Mutations in the Family of Polyposis Patients: A Prospective Study

BACKGROUND

Almost no prospective data on endoscopy in MUTYH monoallelic carriers are available.

OBJECTIVE

This study aimed to define the prevalence of colorectal and duodenal adenomas in a population of people presenting with a single mutation of the MUTYH gene and being first-degree relatives of biallelic MUTYH mutation carriers.

DESIGN

This study is a prospective cohort evaluation.

PATIENTS

Patients were first-degree relatives of a patient who had polyposis with biallelic MUTYH mutation and carrying a single gene mutation of the gene from 12 French centers.

SETTINGS

This is a multicenter study.

INTERVENTION

Detailed data on life habits (tobacco, alcohol, and nonsteroidal anti-inflammatory drugs), extraintestinal manifestations, and germline analysis were recorded. Complete endoscopic evaluation (colonoscopy and upper endoscopy) with chromoendoscopy was performed.

RESULTS

Sixty-two patients were prospectively included (34 women (55%), mean age of 54, range 30-70 years). Thirty-two patients (52%) presented with colorectal polyps at colonoscopy. Of these patients with polyps, 15 (25%) had only adenomas, 8 (13%) had only hyperplastic polyps, 1 (1%) had sessile serrated adenomas, and 8 (13%) had adenomas and/or sessile serrated adenomas. We detected, in total, 29 adenomas with low-grade dysplasia, 5 adenomas with high-grade dysplasia, and 6 sessile serrated adenomas. Fourteen patients (23%) presented with a single adenoma, and 10 (16%) had 1 to 5 adenomas. No patient had more than 5 adenomas. At upper endoscopy, 3 had a limited number of fundic gland polyps; none had duodenal adenomas. The 2 main missense mutations c.1145G>A, p.Gly382Asp and c.494A>G, p.Tyr165Cys were associated with the development of colorectal adenomas/serrated polyps in these monoallelic carriers.

LIMITATIONS

This study was limited by the small number of patients.

CONCLUSIONS

This prospective study provides unique prospective data suggesting that monoallelic mutation carriers related to patients with polyposis show no colorectal polyposis and have very limited upper GI manifestations justifying an endoscopic follow-up. See Video Abstract at http://links.lww.com/DCR/A862.

MutYH-associated polyposis

MutYH-associated polyposis is the only polyposis syndrome with an autosomal recessive type of inheritance, often phenotypically similar to a weakened form of familial adenomatous polyposis. For the development of the disease mutations in both alleles of the gene are required, but an increased risk of developing colorectal cancer in carriers of monoallelic mutations is noted. The diagnosis of MutYH-associated polyposis should be suspected in a patient with colorectal cancer over 45 years old on the background of polyps in the colon. The review presents modern algorithms for diagnostic and treatment of the disease.

Common Genetic Variants of MUTYH are not Associated with Cutaneous Malignant Melanoma: Application of Molecular Screening by Means of High-Resolution Melting Technique in a Pilot Case-Control Study

MUTYH glycosylase recognizes the 8-oxoG:A mismatch and is able to excise the adenine base using proofreading mechanisms. Some papers have reported a strong association between cancer development or aggressiveness and MUTYH gene mutations. The aim of this study was to find a possible association between the most frequent MUTYH mutations and melanoma in the context of a case-control pilot study. One hundred ninety-five melanoma patients and 195 healthy controls were matched for sex and age. Clinical and laboratory data were collected in a specific database and all individuals were analyzed for MUTYH mutations by high-resolution melting and direct sequencing techniques. Men and women had significantly different distributions of tumor sites and phototypes. No significant associations were observed between the Y165C, G382D and V479F MUTYH mutations and risk of melanoma development or aggressiveness. Our preliminary findings therefore do not confirm a role for MUTYH gene mutations in the melanoma risk. Further studies are necessary for the assessment of MUTYH not only in melanoma but also other cancer types with the same embryonic origin, in the context of larger arrays studies of genes involved in DNA stability or integrity.

Inherited Cancer in the Age of Next-Generation Sequencing

Next-generation sequencing (NGS) technology has led to the ability to test for multiple cancer susceptibility genes simultaneously without significantly increasing cost or turnaround time. With growing usage of multigene testing for inherited cancer, ongoing education for nurses and other health-care providers about hereditary cancer screening is imperative to ensure appropriate testing candidate identification, test selection, and posttest management. The purpose of this review article is to (1) provide an overview of how NGS works to detect germline mutations, (2) summarize the benefits and limitations of multigene panel testing, (3) describe risk categories of cancer susceptibility genes, and (4) highlight the counseling considerations for patients pursuing multigene testing.

Association of monoallelic MUTYH mutation among Egyptian patients with colorectal cancer

Colorectal cancer (CRC) is a heterogeneous triat that involves both environmental and genetic factors. Genetic mutations of MUTYH (p.Y179C and p.G396D) have been reported to be associated with increased risk of CRC among several ethnic populations. The aim of this work is to assess the association of the monoallelic MUTYH mutations (p.Y179C and p.G396D) with increased risk of CRC among Egyptian patients. This study included 120 unrelated CRC Egyptian patients who were compared with 100 healthy controls from the same locality. For all individuals, DNA was genotyped for MUTYH p.Y179C and MUTYH p.G396D mutations using the T-ARMS-PCR technique. The frequencies of monoallelic MUTYH mutations showed a strong association with the increased risk of CRC among Egyptian patients compared with controls (12.5 vs. 4.0 %, OR = 3.49, 95 % CI = 1.12-10.90, P = 0.03). Moreover, the frequency of MUTYH p.Y179C mutation was noted to be significantly higher among CRC patients compared to controls rather than MUTYH p.G396D mutation. Interestingly, CRC patients with tumors in the right side colon showed an evidence for association with the MUTYH p.Y179C mutation compared with tumors in the left side colon (p = 0.01). MUTYH p.Y179C mutation was associated with an increased risk of CRC among Egyptian patients rather than MUTYH p.G396D mutation.

Hereditary Colorectal Tumors: A Literature Review on MUTYH-Associated Polyposis

MAP (MUTYH-associated polyposis) is a syndrome, described in 2002, which is associated with colorectal adenomas, with enhanced colorectal carcinogenesis. This review synthesizes the available literature on MAP and outlines its pathogenesis, association with colorectal tumorigenesis, screening, treatment, and the subtle differences between it and its close cousins—FAP and AFAP. The preponderance of data is collected using MAP guidelines. However, although AFAP and MAP appear similar, potentially important distinctions exist, warranting targeted diagnostic criteria and treatment approaches. We suggest that it may be prudent to screen for MAP earlier than in current clinical practice, as it has been shown that sequence variants are associated with more severe disease, presenting with an earlier onset of colorectal cancer. Finally, we issue a call-to-action for much-needed further data to establish clear clinical and diagnostic criteria.

Serum and tissue markers in colorectal cancer: State of art

Colorectal cancer (CRC) represents one of the most commonly diagnosed cancers worldwide. It is the second leading cause of cancer death in Western Countries. In the last decade, the survival of patients with metastatic CRC has improved dramatically. Due to the advent of new drugs (irinotecan and oxaliplatin) and target therapies (i.e. bevacizumab, cetuximab, panitumab, aflibercept and regorafenib), the median overall survival has risen from about 12 mo in the mid nineties to 30 mo recently. Molecular studies have recently widened the opportunity for testing new possible markers, but actually, only few markers can be recommended for practical use in clinic. In the next future, the hope is to have a complete panel of clinical biomarkers to use in every setting of CRC disease, and at the same time: 1) to receive information about prognostic significance by their expression and 2) to be oriented in the choice of the adequate treatment. Moreover, molecular analyses have shown that the natural history of all CRCs is not the same. Individual patients with same stage tumors may have different long-term prognosis and response to therapy. In addition, some prognostic variables are likely to be more important than others. Here we review the role of serum and tissue markers according to the recently published English literature. This paper is an extension of the article "Biological and clinical markers in colorectal cancer: state of art" by Cappellani A published in Jan 2010.

Functional interaction between hMYH and hTRADD in the TNF-α-mediated survival and death pathways of HeLa cells

The tumor necrosis factor (TNF) signaling pathway is a classical immune system pathway that plays a key role in regulating cell survival and apoptosis. The TNF receptor-associated death domain (TRADD) protein is recruited to the death domain of TNF receptor 1 (TNFR1), where it interacts with TNF receptor-associated factor 2 (TRAF2) and receptor-interacting protein (RIP) for the induction of apoptosis, necrosis, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), and mitogen-activated protein (MAP) kinase activation. In this study, we found that the human MutY homolog (hMYH) interacted with human TRADD (hTRADD) via the C-terminal domain of hMYH. Moreover, under conditions promoting TNF-α-induced cell death or survival in HeLa cells, this interaction was weakened or enhanced, respectively. The interaction between hMYH and hTRADD was important for signaling pathways mediated by TNF-α. Our results also suggested that the hTRADD-hMYH association was involved in the nuclear translocation of NFκB and formation of the TNFR1-TRADD complex. Thus, this study identified a novel mechanism through which the hMYH-hTRADD interaction may affect the TNF-α signaling pathway.

IMPLICATIONS

In HeLa cells, the hTRADD-hMYH interaction functioned in both cell survival and apoptosis pathways following TNF-α stimulation.

Low-fidelity compensatory backup alternative DNA repair pathways may unify current carcinogenesis theories

The somatic mutation carcinogenesis theory has dominated for decades. The alternative theory, tissue organization field theory, argues that the development of cancer is determined by the surrounding microenvironment. However, neither theory can explain all features of cancer. As cancers share the features of uncontrolled proliferation and genomic instability, they are likely to have the same pathogenesis. It has been found that various DNA repair pathways within a cell crosstalk with one another, forming a DNA repair network. When one DNA repair pathways is defective, the others may work as compensatory backups. The latter pathways are explored for synthetic lethal anticancer therapy. In this article, we extend the concept of compensatory alternative DNA repair to unify the theories. We propose that the microenvironmental stress can activate low-fidelity compensatory alternative DNA repair, causing mutations. If the mutation occurs to a DNA repair gene, this secondarily mutated gene can lead to even more mutated genes, including those related to other DNA repair pathways, eventually destabilizing the genome. Therefore, the low-fidelity compensatory alternative DNA repair may mediate microenvironment-dependent carcinogenesis. The proposal seems consistent with the view of evolution: the environmental stress causes mutations to adapt to the changing environment.

Genomic instability and radiation risk in molecular pathways to colon cancer

Colon cancer is caused by multiple genomic alterations which lead to genomic instability (GI). GI appears in molecular pathways of microsatellite instability (MSI) and chromosomal instability (CIN) with clinically observed case shares of about 15–20% and 80–85%. Radiation enhances the colon cancer risk by inducing GI, but little is known about different outcomes for MSI and CIN. Computer-based modelling can facilitate the understanding of the phenomena named above. Comprehensive biological models, which combine the two main molecular pathways to colon cancer, are fitted to incidence data of Japanese a-bomb survivors. The preferred model is selected according to statistical criteria and biological plausibility. Imprints of cell-based processes in the succession from adenoma to carcinoma are identified by the model from age dependences and secular trends of the incidence data. Model parameters show remarkable compliance with mutation rates and growth rates for adenoma, which has been reported over the last fifteen years. Model results suggest that CIN begins during fission of intestinal crypts. Chromosomal aberrations are generated at a markedly elevated rate which favors the accelerated growth of premalignant adenoma. Possibly driven by a trend of Westernization in the Japanese diet, incidence rates for the CIN pathway increased notably in subsequent birth cohorts, whereas rates pertaining to MSI remained constant. An imbalance between number of CIN and MSI cases began to emerge in the 1980s, whereas in previous decades the number of cases was almost equal. The CIN pathway exhibits a strong radio-sensitivity, probably more intensive in men. Among young birth cohorts of both sexes the excess absolute radiation risk related to CIN is larger by an order of magnitude compared to the MSI-related risk. Observance of pathway-specific risks improves the determination of the probability of causation for radiation-induced colon cancer in individual patients, if their exposure histories are known.

Abnormality in Wnt signaling is causatively associated with oxidative stress-induced intestinal tumorigenesis in MUTYH-null mice

MUTYH is a DNA glycosylase that excises adenine paired with 8-oxoguanine to prevent mutagenesis in mammals. Biallelic germline mutations of MUTYH have been found in patients predisposed to a recessive form of familial adenomatous polyposis (MAP: MUTYH-associated polyposis). We previously reported that Mutyh-deficient mice showed a high susceptibility to spontaneous and oxidative stress-induced intestinal adenoma/carcinoma. Here, we performed mutation analysis of the tumor-associated genes including Apc, Ctnnb1, Kras and Trp53 in the intestinal tumors of Mutyh-deficient mice. In the 62 tumors, we identified 25 mutations in Apc of 18 tumors and 36 mutations in Ctnnb1 of 36 tumors. Altogether, 54 out of the 62 tumors (87.1%) had a mutation in either Apc or Ctnnb1; no tumor displayed mutations simultaneously in the both genes. Similar to MAP, 60 out of 61 mutations (98.3%) were identified as G:C to T:A transversions of which 85% occurred at either AGAA or TGAA sequences. Immunohistochemical analyses revealed the accumulation of β-catenin in the nuclei of tumors. No mutation was found in either Kras or Trp53 in the tumors. These results indicate that the uncontrolled activation of Wnt signaling pathway is causatively associated with oxidative stress-induced intestinal tumorigenesis in the Mutyh-deficient mice.

High prevalence of the c.1227_1228dup (p.Glu410GlyfsX43) mutation in Tunisian families affected with MUTYH-associated-polyposis

Germline mutations in the base excision repair gene MUTYH have been associated with recessive inheritance of multiple colorectal adenomas. Screening of the MUTYH gene was carried on index cases of 10 unrelated Tunisian families and on available DNA samples from some members. Three germline mutations: c.536A > G (p.Y179C), c.1187 G > A (p.G396D) and c.1227_1228dup (p.Glu410GlyfsX43), were identified in the homozygous or compound heterozygous state in 8 out of 10 families. The c.1227_1228dup (p.Glu410GlyfsX43) mutation was the most frequent, since it was found in biallelic homozygous in 7 probands and 2 members of family F1 and in compound heterozygous associated with the c.536 A > G (p.Y179C) or c.1187 G > A (p.G396D) in family F2. Haplotype analysis revealed that the 8 families are unrelated. Moreover, in sporadic colorectal cancer, the c.1227_1228dup (p.Glu410GlyfsX43) mutation was identified in 13 % of patients compared to the p.G396D and p.Y179C found in 1.2 and 2.12 % respectively. Our data shows the high prevalence of the p.Glu410GlyfsX43 mutation in Tunisian families affected with MUTYH associated polyposis as well as in sporadic colorectal carcinoma.

Why is hepatocellular carcinoma less attributable to viral hepatitis in Yemen?

The hepatitis B virus (HBV) and the hepatitis C virus (HCV) are still public health problems in Yemen, with older individuals having much higher prevalence than younger generations. However, research on the prevalence of viral hepatitis in association with hepatocellular cancer (HCC) has not yet been undertaken in Yemen. The aim of this study was to determine the prevalence of HBV and HCV infection among HCC patients and to estimate the risk of these infections being associated with the development of HCC. A cross-sectional study was conducted on patients attending oncology outpatient in Sana'a, Yemen, through the period 2008-mid 2010 with confirmed diagnosis of HCC. A total of 88 cases were studied thoroughly with different investigations such as CT-scan, ultrasound, tumour marker, alpha-feto-protein and histopathological biopsy. A structured questionnaire was also applied and physical examination done to assess the general condition of the patients. Statistical package (SPSS version 16) was used for analysis of the data. The mean age of the cases was 61.2 years (± 12.6) with half over 60 years. There were fewer male patients (36%) compared to females and most (97%) only had basic /no formal education. Seventy nine (89%) were diagnosed as HCC cases with histopathological biopsy while the rest were diagnosed by ultrasound, CT scan, tumour marker, and alpha-feto-protein. Around one-third of the subjects were positive for HBsAg and HCV antibodies. Multivariate analysis showed infection with HCV and use of smoking was associated with HCC diagnosis. Although an association was observed between the occurrence of HCC and viral hepatitis (either HBV or HCV) and cigarette smoking, but the rate of viral infection was lower than what has been reported elsewhere.

Promoter methylation status of DNA repair gene (hMLH1) in gastric carcinoma patients of the Kashmir valley

Cancer is a multi-factorial disease and variation in genetic susceptibility, due to inherited differences in the capacity to repair mismatches in the genome, is an important factor in the development of gastric cancer (GC), for example. Epigenetic changes, including aberrant methylation of 5/CpG islands in the promoter regions of mismatch repair (MMR) genes like hMLH1, have been implicated in the development of various types of GC. In the present study we evaluated the role of hMLH1 promoter hypermethylation in Kashmiri GC patients and controls, and assessed correlations with various dietary and lifestyle factors. The study included 70 GC patients (56 males and 14 females; age (mean ± S.D) 50 ± 11.4 years). Distinction between methylated and unmethylated was achieved with MS-PCR and DNA band patterns. The Chi-square test was applied to assess the risk due to promoter hypermethylation. We found a strikingly high frequency of promoter hypermethylation in GC cases than in normal samples (72.9% (51/70) in GC cases vs 20% (14/70) in normal samples (p=0.0001). We also observed a statistically significant association between methylated hMLH1 gene promoter and smoking, consumption of sundried vegetables and hot salted tea with the risk of GC. This study revealed that hMLH1 hypermethylation is strongly associated with GC and suggested roles for epigenetic changes in stomach cancer causation in the Kashmir valley.

Mutational spectrum of the APC and MUTYH genes and genotype-phenotype correlations in Brazilian FAP, AFAP, and MAP patients

Background

Patients with multiple colorectal adenomas are currently screened for germline mutations in two genes, APC and MUTYH. APC-mutated patients present classic or attenuated familial adenomatous polyposis (FAP/AFAP), while patients carrying biallelic MUTYH mutations exhibit MUTYH-associated polyposis (MAP). The spectrum of mutations as well as the genotype-phenotype correlations in polyposis syndromes present clinical impact and can be population specific, making important to obtain genetic and clinical data from different populations.

Methods

DNA sequencing of the complete coding region of the APC and MUTYH genes was performed in 23 unrelated Brazilian polyposis patients. In addition, mutation-negative patients were screened for large genomic rearrangements by multiplex ligation-dependent probe amplification, array-comparative genomic hybridization, and duplex quantitative PCR. Biallelic MUTYH mutations were confirmed by allele-specific PCR. Clinical data of the index cases and their affected relatives were used to assess genotype–phenotype correlations.

Results

Pathogenic mutations were identified in 20 of the 23 probands (87%): 14 in the APC gene and six in the MUTYH gene; six of them (30%) were described for the first time in this series. Genotype-phenotype correlations revealed divergent results compared with those described in other studies, particularly regarding the extent of polyposis and the occurrence of desmoid tumors in families with mutations before codon 1444 (6/8 families with desmoid).

Conclusions

This first comprehensive investigation of the APC and MUTYH mutation spectrum in Brazilian polyposis patients showed a high detection rate and identified novel pathogenic mutations. Notably, a significant number of APC-positive families were not consistent with the predicted genotype-phenotype correlations from other populations.

DNA charge transport for sensing and signaling

The DNA duplex is an exquisite macromolecular array that stores genetic information to encode proteins and regulate pathways. Its unique structure also imparts chemical function that allows it also to mediate charge transport (CT). We have utilized diverse platforms to probe DNA CT, using spectroscopic, electrochemical, and even genetic methods. These studies have established powerful features of DNA CT chemistry. DNA CT can occur over long molecular distances as long as the bases are well stacked. The perturbations in base stacking that arise with single base mismatches, DNA lesions, and the binding of some proteins that kink the DNA all inhibit DNA CT. Significantly, single molecule studies of DNA CT show that ground state CT can occur over 34 nm if the duplex is well stacked; one single base mismatch inhibits CT. The DNA duplex is an effective sensor for the integrity of the base pair stack. Moreover, the efficiency of DNA CT is what one would expect for a stack of graphite sheets: equivalent to the stack of DNA base pairs and independent of the sugar-phosphate backbone. Since DNA CT offers a means to carry out redox chemistry from a distance, we have considered how this chemistry might be used for long range biological signaling. We have taken advantage of our chemical probes and platforms to characterize DNA CT in the context of the cell. CT can occur over long distances, perhaps funneling damage to particular sites and insulating others from oxidative stress. Significantly, transcription factors that activate the genome to respond to oxidative stress can also be activated from a distance through DNA CT. Numerous proteins maintain the integrity of the genome and an increasing number of them contain [4Fe-4S] clusters that do not appear to carry out either structural or enzymatic roles. Using electrochemical methods, we find that DNA binding shifts the redox potentials of the clusters, activating them towards oxidation at physiological potentials. We have proposed a model that describes how repair proteins may utilize DNA CT to efficiently search the genome for lesions. Importantly, many of these proteins occur in low copy numbers within the cell, and thus a processive mechanism does not provide a sufficient explanation of how they find and repair lesions before the cell divides. Using atomic force microscopy and genetic assays, we show that repair proteins proficient at DNA CT can relocalize in the vicinity of DNA lesions and can cooperate in finding lesions within the cell. Conversely, proteins defective in DNA CT cannot relocalize in the vicinity of lesions and do not assist other proteins involved in repair within the cell. Moreover such genetic defects are associated with disease in human protein analogues. As we continue to unravel this chemistry and discover more proteins with redox cofactors involved in genome maintenance, we are learning more regarding opportunities for long range signaling and sensing, and more examples of DNA CT chemistry that may provide critical functions within the cell.

MUTYH-associated polyposis (MAP), the syndrome implicating base excision repair in inherited predisposition to colorectal tumors

In 2002, Al-Tassan and co-workers described for the first time a recessive form of inherited polyposis associated with germline mutations of MUTYH, a gene encoding a base excision repair (BER) protein that counteracts the DNA damage induced by the oxidative stress. MUTYH-associated polyposis (MAP) is now a well-defined cancer susceptibility syndrome, showing peculiar molecular features that characterize disease progression. However, some aspects of MAP, including diagnostic criteria, genotype-phenotype correlations, pathogenicity of variants, as well as relationships between BER and other DNA repair pathways, are still poorly understood. A deeper knowledge of the MUTYH expression pattern is likely to refine our understanding of the protein role and, finally, to improve guidances for identifying and handling MAP patients.

Chemical and biological consequences of oxidatively damaged guanine in DNA

Of the four native nucleosides, 2'-deoxyguanosine (dGuo) is most easily oxidized. Two lesions derived from dGuo are 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (Fapy)∙dGuo. Furthermore, while steady-state levels of 8-oxodGuo can be detected in genomic DNA, it is also known that 8-oxodGuo is more easily oxidized than dGuo. Thus, 8-oxodGuo is susceptible to further oxidation to form several hyperoxidized dGuo products. This review addresses the structural impact, the mutagenic and genotoxic potential, and biological implications of oxidatively damaged DNA, in particular 8-oxodGuo, Fapy∙dGuo, and the hyperoxidized dGuo products.

Oxidatively induced DNA damage: mechanisms, repair and disease

Endogenous and exogenous sources cause oxidatively induced DNA damage in living organisms by a variety of mechanisms. The resulting DNA lesions are mutagenic and, unless repaired, lead to a variety of mutations and consequently to genetic instability, which is a hallmark of cancer. Oxidatively induced DNA damage is repaired in living cells by different pathways that involve a large number of proteins. Unrepaired and accumulated DNA lesions may lead to disease processes including carcinogenesis. Mutations also occur in DNA repair genes, destabilizing the DNA repair system. A majority of cancer cell lines have somatic mutations in their DNA repair genes. In addition, polymorphisms in these genes constitute a risk factor for cancer. In general, defects in DNA repair are associated with cancer. Numerous DNA repair enzymes exist that possess different, but sometimes overlapping substrate specificities for removal of oxidatively induced DNA lesions. In addition to the role of DNA repair in carcinogenesis, recent evidence suggests that some types of tumors possess increased DNA repair capacity that may lead to therapy resistance. DNA repair pathways are drug targets to develop DNA repair inhibitors to increase the efficacy of cancer therapy. Oxidatively induced DNA lesions and DNA repair proteins may serve as potential biomarkers for early detection, cancer risk assessment, prognosis and for monitoring therapy. Taken together, a large body of accumulated evidence suggests that oxidatively induced DNA damage and its repair are important factors in the development of human cancers. Thus this field deserves more research to contribute to the development of cancer biomarkers, DNA repair inhibitors and treatment approaches to better understand and fight cancer.

Breakpoint characterization of a novel large intragenic deletion of MUTYH detected in a MAP patient: case report

Background

MUTYH-associated polyposis (MAP) is a recessive, hereditary, colorectal cancer-predisposing syndrome caused by biallelic mutations in the MUTYH gene. Most MUTYH pathogenic variants are missense mutations, and until recently no gross genomic deletions had been described.

Case Presentation

We have identified a large deletion in the MUTYH gene: a > 4.2 kb deletion encompassing exons 4-16. This is the second description of this rearrangement, which has been recently described as the first large deletion in this gene. The clinically suspected MAP patient was homozygous for this mutation and presented with no amplification products for 14 exons of MUTYH on initial screening. Deletion breakpoints were refined to base pair level through array comparative genomic hybridization (aCGH) analysis followed by sequencing. The identified breakpoints were located within intron 3 and 146 bp downstream of the 3' end of the gene, with the presence of an AluJr element adjacent to the distal breakpoint. The presence of a 2 bp insertion at the junction suggests the involvement of the non-homologous end joining (NHEJ) repair mechanism, possibly facilitated by rearrangement-promoting elements. Examination of the MUTYH locus revealed a high Alu density that may make this region prone to rearrangements.

Conclusion

Large deletions are a possible mechanism for loss of function of the MUTYH gene, and investigation of such mutations may be important in identifying causative mutations in MAP patients.

High resolution melting analysis for a rapid identification of heterozygous and homozygous sequence changes in the MUTYH gene

Background

MUTYH-associated polyposis (MAP) is an autosomal recessive form of intestinal polyposis predisposing to colorectal carcinoma. High resolution melting analysis (HRMA) is a mutation scanning method that allows detection of heterozygous sequence changes with high sensitivity, whereas homozygosity for a nucleotide change may not lead to significant curve shape or melting temperature changes compared to homozygous wild-type samples. Therefore, HRMA has been mainly applied to the detection of mutations associated with autosomal dominant or X-linked disorders, while applications to autosomal recessive conditions are less common.

Methods

MUTYH coding sequence and UTRs were analyzed by both HRMA and sequencing on 88 leukocyte genomic DNA samples. Twenty-six samples were also examined by SSCP. Experiments were performed both with and without mixing the test samples with wild-type DNA.

Results

The results show that all MUTYH sequence variations, including G > C and A > T homozygous changes, can be reliably identified by HRMA when a condition of artificial heterozygosity is created by mixing test and reference DNA. HRMA had a sensitivity comparable to sequencing and higher than SSCP.

Conclusions

The availability of a rapid and inexpensive method for the identification of MUTYH sequence variants is relevant for the diagnosis of colorectal cancer susceptibility, since the MAP phenotype is highly variable.

The genomics of colorectal cancer: state of the art

The concept of the adenoma-carcinoma sequence, as first espoused by Morson et al. whereby the development of colorectal cancer is dependent on a stepwise progression from adenomatous polyp to carcinoma is well documented. Initial studies of the genetics of inherited colorectal cancer susceptibility concentrated on the inherited colorectal cancer syndromes, such as Familial Adenomatous Polyposis (FAP) and Lynch Syndrome (also known as HNPCC). These syndromes, whilst easily characterisable, have a well understood sequence of genetic mutations that predispose the sufferer to developing colorectal cancer, initiated for example in FAP by the loss of the second, normal allelle of the tumour supressor APC gene. Later research has identified other inherited variants such as MUTYH (MYH) polyposis and Hyperplastic Polyposis Syndrome. Recent research has concentrated on the pathways by which colorectal adenomatous polyps not due to one of these known inherited susceptibilities undergo malignant transformation, and determination of the types of polyps most likely to do so. Also, why do individuals in certain families have a predisposition to colorectal cancer. In this article, we will discuss briefly the current state of knowledge of the genomics of the classical inherited colorectal cancer syndromes. We will also discuss in detail the genetic changes in polyps that undergo malignant transformation as well as current knowledge with regards to the epigenomic changes found in colorectal polyps.

MUTYH Associated Polyposis (MAP)

MUTYH Associated Polyposis (MAP), a Polyposis predisposition caused by biallelic mutations in the Base Excision Repair (BER) gene MUTYH, confers a marked risk of colorectal cancer (CRC). The MAP phenotype is difficult to distinguish from other hereditary CRC syndromes. Especially from Familial Adenomatous Polyposis (FAP) and to a lesser extend Lynch Syndrome, which are caused by germline mutations in the APC and Mismatch Repair (MMR) genes, respectively.

Here we review research findings regarding MUTYH interactions, genotypic and phenotypic characteristics of MAP, as well as surveillance and treatment of the disease. The applied papers, published between 1/1 2002- 1/2 2008, were found through PubMed.

The exact role of MUTYH in CRC tumorgenesis is still uncertain, although MAP tumors show distinct molecular features, including somatic G:C>T:A transversions in the APC gene. Furthermore, cooperation between the BER and the MMR systems exists, as MUTYH interacts with MMR gene-products. Possibly, monoallelic defects in both pathways are of significance to CRC development.

Specific MUTYH variants are found to be characteristic in distinct ethnic populations, which could facilitate future genetic screening. Knowledge concerning functional consequences of many MUTYH germline mutations remains sparse. Most thoroughly investigated are the two most common MUTYH variants, Y179C and G396D, both generating dysfunctional gene products.

Phenotypic features of MAP include: development of 10-100 colorectal adenomas, debuting at 46-47 years, often CRC at time of clinical diagnosis, and in some, development of extracolonic manifestations.

Extra nuchal-type fibroma associated with elastosis, traumatic neuroma, a rare APC gene missense mutation, and a very rare MUTYH gene polymorphism: a case report and review of the literature*

We report a case of an extra nuchal-type fibroma in a 51-year-old male suspected to have attenuated familial adenomatous polyposis (Gardner's syndrome), who presented with a longstanding buttock mass excised due to enlargement and pain. Histopathologically, lobules of haphazard, hypocellular, hyalinized collagen bundles replaced the dermis and subcutis and entrapped nerve bundles, mimicking Morton neuroma. Ramifying nerve twigs found around larger nerve fascicles showed the co-existence of traumatic neuroma. Elastic tissue stain revealed elastosis characterized by large, arborizing fibers lying between and within the hyalinized collagen bundles. Modified Masson's trichrome stain showed light blue staining of collagen bundles producing the hyalinized nodules with irregular, light red staining of collagen bundles at their periphery and within tumor collagen. Compression and/or degeneration of collagen and secondary elastosis with later entrapment by tumor collagen could explain this microscopic phenotype. By immunohistochemistry, tumor spindle cells expressed nuclear β-catenin and cyclin D1, mostly within regions of fibrosis implicating activation of the adenomatous polyposis coli (APC)-Wnt pathway. Genetic analysis showed a missense mutation in APC gene (c.7504G>A, p.G2502S in exon 15) and a functional homozygous polymorphism in the MUTYH gene (c.36+325G>C, (IVS1+5G/C)). Nuchal-type fibroma has been associated with Gardner's syndrome and trauma. In this patient, genetic predisposition coupled with repetitive, localized trauma and collagen degeneration may have provided the stimulus for the development of extra nuchal-type fibroma.

Frequency of the common germline MUTYH mutations p.G396D and p.Y179C in patients diagnosed with colorectal cancer in Southern Brazil

INTRODUCTION

MUTYH-associated polyposis (MAP) is an autosomal recessive cancer predisposition syndrome associated with the development of colorectal tumors and colonic polyps at an early age. MAP syndrome is associated to germline biallelic mutations in the MUTYH gene which lead to deficient DNA repair through the base-excision repair system and accumulation of G:C→T:A transversions. Occurrence of such mutations in oncogenes and tumor suppressor genes drives colorectal carcinogenesis and is associated with the development of colonic polyps. Two common mutations, p.Y179C and p.G396D, are present in approximately 70-80% of MAP in European families with identified MUTYH germline mutations. The aim of this study was to assess the frequency of the germline MUTYH mutations p.Y179C and p.G396D in Brazilian patients with MAP and other hereditary colorectal cancer (CRC) phenotypes, as well as in sporadic CRC cases.

MATERIALS AND METHODS

A total of 75 patients were included. Samples were screened for the MUTYH germline mutations p.Y179C and p.G396D by allelic discrimination assays using allele-specific TaqMan® probes. In all mutation-positive cases, results were confirmed by sequencing.

RESULTS AND CONCLUSIONS

Biallelic germline MUTYH mutations were identified in 4 of 60 (6.6%) patients with a phenotype of hereditary colorectal cancer. Germline MUTYH mutation screening should be considered in the differential diagnosis of hereditary colorectal syndromes, and not only in MAP, but also in familial adenomatous polyposis and Bethesda criteria-positive families. Additional mutation screening studies of the MUTYH gene in a larger number of Brazilian patients will be necessary to confirm these results and determine the validity and applicability of MUTYH mutation screening in our population.

Mutants of the base excision repair glycosylase, endonuclease III: DNA charge transport as a first step in lesion detection

Endonuclease III (EndoIII) is a base excision repair glycosylase that targets damaged pyrimidines and contains a [4Fe-4S] cluster. We have proposed a model where BER proteins that contain redox-active [4Fe-4S] clusters utilize DNA charge transport (CT) as a first step in the detection of DNA lesions. Here, several mutants of EndoIII were prepared to probe their efficiency of DNA/protein charge transport. Cyclic voltammetry experiments on DNA-modified electrodes show that aromatic residues F30, Y55, Y75, and Y82 help mediate charge transport between DNA and the [4Fe-4S] cluster. On the basis of circular dichroism studies to measure protein stability, mutations at residues W178 and Y185 are found to destabilize the protein; these residues may function to protect the [4Fe-4S] cluster. Atomic force microscopy studies furthermore reveal a correlation in the ability of mutants to carry out protein/DNA CT and their ability to relocalize onto DNA strands containing a single base mismatch; EndoIII mutants that are defective in carrying out DNA/protein CT do not redistribute onto mismatch-containing strands, consistent with our model. These results demonstrate a link between the ability of the repair protein to carry out DNA CT and its ability to relocalize near lesions, thus pointing to DNA CT as a key first step in the detection of base damage in the genome.

Association between monoallelic MUTYH mutation and colorectal cancer risk: a meta-regression analysis

Whether people who inherit a mutation in MUTYH from only one parent (monoallelic mutation) are at increased risk of colorectal cancer (CRC) remains controversial. Most previous studies and meta-analyses have not found statistically significant associations but, given carriers are relatively rare, may be underpowered to detect small increased risks. We have conducted a systematic review and meta-regression analysis of previously published case-control studies to estimate the strength of association for monoallelic MUTYH mutation and CRC risk. Potential sources of heterogeneity were evaluated. We have compared the carrier frequency in cases with a family history of CRC to that of controls, as a novel and powerful design, to measure statistical evidence of an association but not the strength of association. The magnitude of the genotype-disease association, estimated from a pooled odds ratio comparing cases unselected for family history with controls, was 1.15 (95% CI = 0.98-1.36) and not substantially altered by adjustment for potential sources of heterogeneity. Monoallelic mutation carrier frequency was greater for cases ascertained due to a family history (3.3%; SE 0.9%) than for controls (1.4%; SE 0.3%) (P = 0.02). Monoallelic MUTYH mutation carriers are at increased risk of CRC but the average increase is small.

Molecular genetics of colorectal cancer

Over the past three decades, molecular genetic studies have revealed some critical mutations underlying the pathogenesis of the sporadic and inherited forms of colorectal cancer (CRC). A relatively limited number of oncogenes and tumor-suppressor genes-most prominently the APC, KRAS, and p53 genes-are mutated in a sizeable fraction of CRCs, and a larger collection of genes that are mutated in subsets of CRC have begun to be defined. Together with DNA-methylation and chromatin-structure changes, the mutations act to dysregulate conserved signaling networks that exert context-dependent effects on critical cell phenotypes, including the regulation of cellular metabolism, proliferation, differentiation, and survival. Much work remains to be done to fully understand the nature and significance of the individual and collective genetic and epigenetic defects in CRC. Some key concepts for the field have emerged, two of which are emphasized in this review. Specifically, the gene defects in CRC often target proteins and pathways that exert pleiotropic effects on the cancer cell phenotype, and particular genetic and epigenetic alterations are linked to biologically and clinically distinct subsets of CRC.

MUTYH-associated polyposis - variability of the clinical phenotype in patients with biallelic and monoallelic MUTYH mutations and report on novel mutations

To further characterize 215 APC mutation-negative patients with colorectal neoplasias classified in classical, attenuated, or atypical familial adenomatous polyposis (FAP) coli we performed mutation screening in the Mut Y homologue (MUTYH) gene. The incidence was 15% for biallelic and 3.7% for monoallelic MUTYH mutations. We describe six novel MUTYH mutations in biallelic constellation and two novel monoallelic missense mutations. Of 33 MUTYH-associated polyposis coli (MAP) patients 57% were attenuated familial adenomatous polyposis (AFAP) patients, 10% display early-onset classical FAP and 18% had only few adenomas at higher age. Biallelic cases had a high incidence of extracolonic polyposis in 32% and colorectal cancer (CRC) in 33% of the cases. The clinical picture of MAP ranged from classical FAP or synchronous CRC at age 30 years to few adenomas at age 54 years without evidence of CRC, initially suspected for hereditary non-polyposis colorectal cancer (HNPCC). The mean age of onset was 43 years, with 11 (33%) patients being younger than 40 years of age, indicating that the clinical manifestation can be earlier than so far reported. Monoallelic MUTYH mutation carriers had a positive family history in seven of eight cases allowing the hypothesis of a disease-causing synergism of MUTYH mutations with other genes.

Frequent mutation in North African patients with MUTYH-associated polyposis

MUTYH-associated polyposis (MAP) has been characterized as an autosomal recessive disease predisposing to a variable number of colorectal adenomas with a high risk of cancer. Numerous studies have indicated that two missense mutations (Y179C and G396D) account for about 80% of MUTYH allelic variants in Europeans. Ethnic and geographic differences in the mutation spectrum have been observed. The aim of this study was to report mutations in patients from North Africa, determine the incidence of the c.1227_1228dup mutation in our cohort of MUTYH patients and to evaluate the existence of a founder effect. Within a group of 36 families with MAP, 11 were shown to have a homozygous c.1227_1228dup mutation. These families came from Algeria (n = 5), Tunisia (n = 4), Morocco (n = 1) and Portugal (n = 1). Probands belonging to families of North African origin showed a significantly higher frequency of c.1227_1228dup (78.6% vs 4.5%, p < 0.0001). Haplotype analyses were performed using 10 microsatellite markers surrounding the MUTYH gene spanning a region of 4.4 cM. We identified a common haplotype of at least 1.3 cM in all families suggesting a founder effect for this mutation.

Ser 524 is a phosphorylation site in MUTYH and Ser 524 mutations alter 8-oxoguanine (OG): a mismatch recognition

MUTYH-associated polyposis (MAP) is a colorectal cancer predisposition syndrome that is caused by inherited biallelic mutations in the base excision repair (BER) gene, MUTYH. MUTYH is a DNA glycosylase that removes adenine (A) misinserted opposite 8-oxo-7,8-dihydro-2'-deoxyguanosine (OG). In this work, wild type (WT) MUTYH overexpressed using a baculovirus-driven insect cell expression system (BEVS) provided significantly higher levels of enzyme compared to bacterial overexpression. The isolated MUTYH enzyme was analyzed for potential post-translational modifications using mass spectrometry. An in vivo phosphorylation site was validated at Serine 524, which is located in the C-terminal OG recognition domain within the proliferating cell nuclear antigen (PCNA) binding region. Characterization of the phosphomimetic (S524D) and phosphoablating (S524A) mutants together with the observation that Ser 524 can be phosphorylated suggest that this residue may play an important regulatory role in vivo by altering stability and OG:A mismatch affinity.

An in-frame exon-skipping MUTYH mutation is associated with early-onset colorectal cancer

PURPOSE

MUTYH-associated polyposis syndrome is inherited as a recessive trait and is characterized by the presence of colorectal adenomas and cancer predisposition. Carriers of biallelic mutations in the base excision repair gene MUTYH are exposed to an increased risk of colorectal cancer. The aim of this study was to investigate the pathogenicity of the 13-base-pair deletion, c.504 + 19_504 + 31del13, located on intron 6 of the MUTYH gene, which was identified in 2 unrelated Greek patients with MUTYH-associated polyposis.

METHODS

Genomic DNA and total RNA were extracted from peripheral blood lymphocytes of 2 unrelated families with polyposis. Screening of the entire coding region of the APC gene and MUTYH gene was performed by direct sequencing.

RESULTS

cDNA analysis of a patient homozygous for the c.504 + 19_504 + 31del13 mutation, and a patient heterozygous for the c.504 + 19_504 + 31del13/c.1437_1439delGGA mutations, revealed complete skipping of MUTYH exon 6. A part of the glycosylase catalytic domain, the pseudo-helix-hairpin-helix motif, is located within exon 6, which enhances the pathogenic effect of the mutation.

CONCLUSION

This study demonstrates a rare pathogenic MUTYH mutation that is possibly associated with a relatively severe MUTYH-associated polyposis phenotype, highlighted by early-onset colorectal cancer. These data can become useful in clinical practice for the appropriate surveillance and management of families with MUTYH-associated polyposis. It is evident that each MUTYH-associated polyposis case should be handled according to its distinct genotype, following a specific prophylaxis protocol to ensure cancer prevention.

Functional analysis of MUTYH mutated proteins associated with familial adenomatous polyposis

The MUTYH DNA glycosylase specifically removes adenine misincorporated by replicative polymerases opposite the oxidized purine 8-oxo-7,8-dihydroguanine (8-oxoG). A defective protein activity results in the accumulation of G>T transversions because of unrepaired 8-oxoG:A mismatches. In humans, MUTYH germline mutations are associated with a recessive form of familial adenomatous polyposis and colorectal cancer predisposition (MUTYH-associated polyposis, MAP). Here we studied the repair capacity of the MUTYH variants R171W, E466del, 137insIW, Y165C and G382D, identified in MAP patients. Following expression and purification of human proteins from a bacterial system, we investigated MUTYH incision capacity on an 8-oxoG:A substrate by standard glycosylase assays. For the first time, we employed the surface plasmon resonance (SPR) technology for real-time recording of the association/dissociation of wild-type and MUTYH variants from an 8-oxoG:A DNA substrate. When compared to the wild-type protein, R171W, E466del and Y165C variants showed a severe reduction in the binding affinity towards the substrate, while 137insIW and G382D mutants manifested only a slight decrease mainly due to a slower rate of association. This reduced binding was always associated with impairment of glycosylase activity, with adenine removal being totally abrogated in R171W, E466del and Y165C and only partially reduced in 137insIW and G382D. Our findings demonstrate that SPR analysis is suitable to identify defective enzymatic behaviour even when mutant proteins display minor alterations in substrate recognition.

Undefined familial colorectal cancer

Colorectal cancer (CRC), one of the most common cancers of the world, is actually a spectrum of several subtypes, with different molecular profiles, clinico-pathological characteristics and possibly separate pathways of progression. It is estimated that in approximately 25%-35% of cases, a familial component exists, so they are classified as familial CRC (fCRC). However the known hereditary CRC syndromes justify only up to 5%. The rest are attributed to some inherited genetic predisposition passed to offspring through low-penetrance genes, which in the proper environmental setting can bring on tumorigenesis. Furthermore, part of the familial clustering may be attributed to chance. Because of the complexity regarding the etiology of CRC, the clinician is sometimes faced with obscure patient data, and cannot be sure if they are dealing with fCRC or sporadic CRC. The elucidation of what is going on with the as yet “undefined” portion of CRC will aid not only in the diagnosis, classification and treatment of CRC, but more importantly in the proper adjustment of the screening guidelines and in genetic counselling of patients.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is characterized by the development of many tens to thousands of adenomas in the rectum and colon during the second decade of life. FAP has an incidence at birth of about 1/8,300, it manifests equally in both sexes, and accounts for less than 1% of colorectal cancer (CRC) cases. In the European Union, prevalence has been estimated at 1/11,300-37,600. Most patients are asymptomatic for years until the adenomas are large and numerous, and cause rectal bleeding or even anemia, or cancer develops. Generally, cancers start to develop a decade after the appearance of the polyps. Nonspecific symptoms may include constipation or diarrhea, abdominal pain, palpable abdominal masses and weight loss. FAP may present with some extraintestinal manifestations such as osteomas, dental abnormalities (unerupted teeth, congenital absence of one or more teeth, supernumerary teeth, dentigerous cysts and odontomas), congenital hypertrophy of the retinal pigment epithelium (CHRPE), desmoid tumors, and extracolonic cancers (thyroid, liver, bile ducts and central nervous system). A less aggressive variant of FAP, attenuated FAP (AFAP), is characterized by fewer colorectal adenomatous polyps (usually 10 to 100), later age of adenoma appearance and a lower cancer risk. Some lesions (skull and mandible osteomas, dental abnormalities, and fibromas on the scalp, shoulders, arms and back) are indicative of the Gardner variant of FAP. Classic FAP is inherited in an autosomal dominant manner and results from a germline mutation in the adenomatous polyposis (APC) gene. Most patients (~70%) have a family history of colorectal polyps and cancer. In a subset of individuals, a MUTYH mutation causes a recessively inherited polyposis condition, MUTYH-associated polyposis (MAP), which is characterized by a slightly increased risk of developing CRC and polyps/adenomas in both the upper and lower gastrointestinal tract. Diagnosis is based on a suggestive family history, clinical findings, and large bowel endoscopy or full colonoscopy. Whenever possible, the clinical diagnosis should be confirmed by genetic testing. When the APC mutation in the family has been identified, genetic testing of all first-degree relatives should be performed. Presymptomatic and prenatal (amniocentesis and chorionic villous sampling), and even preimplantation genetic testing is possible. Referral to a geneticist or genetic counselor is mandatory. Differential diagnoses include other disorders causing multiple polyps (such as Peutz-Jeghers syndrome, familial juvenile polyps or hyperplastic polyposis, hereditary mixed polyposis syndromes, and Lynch syndrome). Cancer prevention and maintaining a good quality of life are the main goals of management and regular and systematic follow-up and supportive care should be offered to all patients. By the late teens or early twenties, colorectal cancer prophylactic surgery is advocated. The recommended alternatives are total proctocolectomy and ileoanal pouch or ileorectal anastomosis for AFAP. Duodenal cancer and desmoids are the two main causes of mortality after total colectomy, they need to be identified early and treated. Upper endoscopy is necessary for surveillance to reduce the risk of ampullary and duodenal cancer. Patients with progressive tumors and unresectable disease may respond or stabilize with a combination of cytotoxic chemotherapy and surgery (when possible to perform). Adjunctive therapy with celecoxib has been approved by the US Food and Drug Administration and the European Medicines Agency in patients with FAP. Individuals with FAP carry a 100% risk of CRC; however, this risk is reduced significantly when patients enter a screening-treatment program.