MUTYH-associated polyposis: Is it time to change upper gastrointestinal surveillance? A single-center case series and a literature overview

BACKGROUND The presence of Spigelman stage(SS)IV duodenal polyposis is considered the most significant risk factor for duodenal cancer in patients with MUTYH-associated polyposis(MAP).However,advanced SS disease is rarely reported in MAP patients,and no clear recommendations on small bowel(SB)surveillance have been proposed in this patient setting.AIM To research more because that case reports of duodenal cancers in MAP suggest that they may develop in the absence of advanced benign SS disease and often involve the distal portion of the duodenum.METHODS We describe a series of MAP patients followed up at the Regina Elena National Cancer Institute of Rome(Italy).A literature overview on previously reported SB cancers in MAP is also provided.RESULTS We identified two(6%)SB adenocarcinomas with no previous history of duodenal polyposis.Our observations,supported by literature evidence,suggest that the formula for staging duodenal polyposis and predicting risk factors for distal duodenum and jejunal cancer may need to be adjusted to take this into account rather than focusing solely on the presence or absence of SS IV disease.Core Tip:Case reports of duodenal cancers in MUTYH-associated polyposis suggest that they may develop in the absence of advanced Spigelman stage(SS)benign disease and often involve the distal portion of the duodenum.In our case series,we identified two(6%)small-bowel adenocarcinomas with no previous history of duodenal polyposis.Our observations,supported by literature evidence,suggest that the formula for staging duodenal polyposis and predicting risk factors for distal duodenum and jejunal cancer should be adjusted to take into consideration the presence of SS IV disease,rather than focusing only on this feature.suggestive of invasive adenocarcinoma.

Hereditary gastrointestinal polyposis: Diagnosis, genetic test and risk assessment

Colorectal cancer (CRC) is the second cause of cancer deaths, with over 1 million new cases estimated every year. Familial adenomatous polyposis, MUTYH-associated polyposis and hamartomatous polyposis are inherited syndromes that account for 2%-5% of all colon cancer. The mutated genes responsible for the vast majority of these disorders, are now known (MLH1, MSH2, MSH6, PMS2, APC, MYH, LKB1, SMAD4, BMPR1A, and PTEN) and specific mutations have been identified. Molecular caracterization of inherited CRCs allows pre-symptomatic diagnosis identifying at-risk individuals and improving cancer surveillance. Adenomatous polyposis includes familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and MUTYH-associated polyposis (MAP). Hamartomatous polyposis comprises Peutz-Jeghers syndrome (PJS), juvenile polyposis syndrome (JPS) and “PTEN hamartoma tumour syndrome” (PHTS). MAP is an autosomal recessive condition, while all other disorders are inherited in an autosomal dominant manner. Differential dyagnosis could be very difficult between syndromes because of their phenotypic variability. Attenuated FAP, MAP and Lynch syndrome could be all associated with fewer numbers of adenomas (3-10 polyps), nevertheless, each syndrome has distinct cancer risks, characteristic clinical features, and separate genetic etiologies. Thus, differential diagnosis is essential for correct management of the specific disease. In our laboratory we set up a methodology for genetic tests of the colorectal polyposis syndrome. In these reviews we summarize the literature data and our experience about diagnosis, genetic tests and cancer risk assesment associated with colorectal polyposis. According to literature data, in our experience, there is a portion of analyzing patients that remain without identified mutation, after molecular screening of the specific gene involved in the pathogenesis of the disease. Since the sensibility of used techniques, such as DHPLC, MLPA and sequencing, is now very high, we suggest that a different approach to molecular diagnosis of polyposis syndromes is necessary. In our laboratory, we are now planning to set up analysis of a larger pannel of genes that could be involved in colorectal poliposis syndromes, using a next generation sequencing techniques. In our opinion, a better characterization of molecular basis of the polyposis syndromes will allow a more efficient cancer prevention.

Early-onset colorectal cancer:A sporadic or inherited disease?

Colorectal cancer is the third most common cancer diagnosed worldwide. Although epidemiology data show a marked variability around the world, its overall incidence rate shows a slow but steady decrease, mainly in developed countries. Conversely, early-onset colorectal cancer appears to display an opposite trend with an overall prevalence in United States and European Union ranging from 3.0% and 8.6%. Colorectal cancer has a substantial proportion of familial cases. In particular, early age at onset is especially suggestive of hereditary predisposition. The clinicopathological and molecular features of colorectal cancer cases show a marked heterogeneity not only between early- and late-onset cases but also within the early-onset group. Two distinct subtypes of early-onset colorectal cancers can be identified: a “sporadic” subtype, usually without family history, and an inherited subtype arising in the context of well defined hereditary syndromes. The pathogenesis of the early-onset disease is substantially well characterized in the inherited subtype, which is mainly associated to the Lynch syndrome and occasionally to other rare mendelian diseases, whereas in the “sporadic” subtype the origin of the disease may be attributed to the presence of various common/rare genetic variants, so far largely unidentified, displaying variable penetrance. These variants are thought to act cumulatively to increase the risk of colorectal cancer, and presumably to also anticipate its onset. Efforts are ongoing in the attempt to unravel the intricate genetic basis of this “sporadic” early-onset disease. A better knowledge of molecular entities and pathways may impact on family-tailored prevention and clinical management strategies.

Impaired suppressive activities of human MUTYH variant proteins against oxidative mutagenesis

AIM:To investigate the suppressive activity of MUTYH variant proteins against mutations caused by oxidative lesion,8-hydroxyguanine(8OHG),in human cells.METHODS:p.R154H,p.M255V,p.L360P,and p.P377L MUTYH variants,which were previously found in patients with colorectal polyposis and cancer,were selected for use in this study.Human H1299 cancer cell lines inducibly expressing wild-type(WT) MUTYH(type 2) or one of the 4 above-mentioned MUTYH variants were established using the piggyBac transposon vector system,enabling the genomic integration of the transposon sequence for MUTYH expression.MUTYH expression was examined after cumate induction using Western blotting analysis and immunofluorescence analysis.The intracellular localization of MUTYH variants tagged with FLAG was also immunofluorescently examined.Next,the mutation frequency in the supF of the shuttle plasmid pMY189 containing a single 8OHG residue at position 159 of the supF was compared between empty vector cells and cells expressing WT MUTYH or one of the 4 MUTYH variants using a supF forward mutation assay.RESULTS:The successful establishment of human cell lines inducibly expressing WT MUTYH or one of the 4 MUTYH variants was concluded based on the detection of MUTYH expression in these cell lines after treatment with cumate.All of the MUTYH variants and WT MUTYH were localized in the nucleus,and nuclear localization was also observed for FLAG-tagged MUTYH.The mutation frequency of supF was 2.2 × 10-2 in the 8OHG-containing pMY189 plasmid and 2.5 × 10-4 in WT pMY189 in empty vector cells,which was an 86-fold increase with the introduction of 8OHG.The mutation frequency(4.7 × 10-3) of supF in the 8OHG-containing pMY189 plasmid in cells overexpressing WT MUTYH was significantly lower than in the empty vector cells(P < 0.01).However,the mutation frequencies of the supF in the 8OHG-containing pMY189 plasmid in cells overexpressing the p.R154H,p.M255V,p.L360P,or p.P377L MUTYH variant were 1.84 × 10-2,1.55 × 10-2,1.91 × 10-2,and 1.96 × 10-2,respectively,meaning that no significant difference was observed in the mutation frequency between the empty vector cells and cells overexpressing MUTYH mutants.CONCLUSION:The suppressive activities of p.R154H,p.M255V,p.L360P,and p.P377L MUTYH variants against mutations caused by 8OHG are thought to be severely impaired in human cells.