MUTYH-associated Polyposis Research Articles

Gastrointestinal tract cancers: Genetics, heritability and germ line mutations.

Gastrointestinal (GI) tract cancers that arise due to genetic mutations affect a large number of individuals worldwide. Even though many of the GI tract cancers arise sporadically, few of these GI tract cancers harboring a hereditary predisposition are now recognized and well characterized. These include Cowden syndrome, MUTYH-associated polyposis, hereditary pancreatic cancer, Lynch syndrome, Peutz-Jeghers syndrome, familial adenomatous polyposis (FAP), attenuated FAP, serrated polyposis syndrome, and hereditary gastric cancer. Molecular characterization of the genes that are involved in these syndromes was useful in the development of genetic testing for diagnosis and also facilitated understanding of the genetic basis of GI cancers. Current knowledge on the genetics of GI cancers with emphasis on heritability and germ line mutations forms the basis of the present review.

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.

Type and frequency of MUTYH variants in Italian patients with suspected MAP: a retrospective multicenter study.

To determine prevalence, spectrum and genotype-phenotype correlations of MUTYH variants in Italian patients with suspected MAP (MUTYH-associated polyposis), a retrospective analysis was conducted to identify patients who had undergone MUTYH genetic testing from September 2002 to February 2014. Results of genetic testing and patient clinical characteristics were collected (gender, number of polyps, age at polyp diagnosis, presence of colorectal cancer (CRC) and/or other cancers, family data). The presence of large rearrangements of the MUTYH gene was evaluated by Multiplex Ligation-dependent Probe Amplification analysis. In all, 299 patients with colorectal neoplasia were evaluated: 61.2% were males, the median age at polyps or cancer diagnosis was 50 years (16-80 years), 65.2% had <100 polyps and 51.8% had CRC. A total of 36 different MUTYH variants were identified: 13 (36.1%) were classified as pathogenetic, whereas 23 (63.9%) were variants of unknown significance (VUS). Two pathogenetic variants were observed in 78 patients (26.1%). A large homozygous deletion of exon 15 was found in one patient (<1.0%). MAP patients were younger than those with negative MUTYH testing at polyps diagnosis (P<0.0001) and at first cancer diagnosis (P=0.007). MAP patients carrying the p.Glu480del variant presented with a younger age at polyp diagnosis as compared to patients carrying p.Gly396Asp and p.Tyr179Cys variants. A high heterogeneity of MUTYH variants and a high rate of VUS were identified in a cohort of Italian patients with suspected MAP. Genotype-phenotype analysis suggests that the p.Glu480del variant is associated with a severe phenotype.

Colorectal Adenomatous Polyposis: Heterogeneity of Susceptibility Gene Mutations and Phenotypes in a Cohort of Italian Patients.

Colorectal adenomatous polyposis entailing cancer predisposition is caused by constitutional mutations in different genes. APC is associated with the familial adenomatous polyposis (FAP/AFAP) and MUTYH with the MUTYH-associated polyposis (MAP), while POLE and POLD1 mutations cause the polymerase proofreading-associated polyposis (PPAP). We screened for mutations in patients with multiple adenomas/FAP: 121 patients were analyzed for APC and MUTYH mutations, and 36 patients were also evaluated for POLE and POLD1 gene mutations. We found 20 FAP/AFAP, 15 MAP, and no PPAP subjects: pathogenic mutations proved to be heterogeneous, and included 5 APC and 1 MUTYH novel mutations. The mutation detection rate was significantly different between patients with 5-100 polyps and those with >100 polyps (p = 8.154 × 10-7), with APC mutations being associated with an aggressive phenotype (p = 1.279 × 10-9). Mean age at diagnosis was lower in FAP/AFAP compared to MAP (p = 3.055 × 10-4). Mutation-negative probands showed a mean age at diagnosis that was significantly higher than FAP/AFAP (p = 3.46986 × 10-7) and included 45.3% of patients with <30 polyps and 70.9% of patients with no family history. This study enlarges the APC and MUTYH mutational spectra, and also evaluated variants of uncertain significance, including the MUTYH p.Gln338His mutation. Moreover this study underscores the phenotypic heterogeneity and genotype-phenotype correlations in a cohort of Italian patients.

Formas hereditarias de cáncer colorrectal

Colorectal cancer is one of the most frequent neoplasms in western countries; it is the third most common cancer in men after prostate and lung cancer and the second most common in women after breast cancer. Colorectal cancer is usually sporadic but in a small proportion is hereditary. The genetic cause is well established, allowing pre-symptomatic diagnosis in at-risk relatives. The present article reviews the most novel findings presented at the latest meeting of the American Gastroenterological Association on hereditary forms of colorectal cancer, especially Lynch syndrome and MUTYH-associated polyposis, as well as diverse organisational aspects that can favour the correct management of these patients and their relatives.

Toward a Molecular Classification of Synchronous Colorectal Cancer: Clinical and Molecular Characterization

BackgroundTwo or more primary colorectal tumors coexisting at the time of diagnosis are considered to be synchronous tumors. It is estimated that synchronous colorectal cancer (SCRC) only accounts for 1.1% to 8.1% of all colorectal cancers (CRCs), and its molecular basis is still poorly understood. Patients and MethodsWe evaluated the microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP) statuses in a series of 49 patients (98 tumors) diagnosed with sporadic SCRC at the 12 de Octubre University Hospital with the aim of improving the molecular characterization of this type of tumor. We considered Lynch syndrome, familial adenomatous polyposis, and MUTYH-associated polyposis (MAP) as exclusion criteria. ResultsMolecular subgrouping on the basis of MSI and CIMP enabled us to define 4 groups that corresponded to the molecular classification proposed for single-tumor CRC. We observed a significant predominance of MSI tumors at the right side regardless of the methylation pattern, and a significant prevalence of microsatellite-stable tumors either at the left side or throughout the entire colon (P = .026). Furthermore, we defined some molecular features frequently observed in sporadic SCRC such as a low-frequency of MSI (8.2%). We observed a high concordance in terms of MSI between simultaneous tumors (93.9%) and a lower concordance in terms of CIMP (51%) between such tumors. ConclusionOur findings support the hypothesis that SCRC involves an environmental rather than a genetic component in which various etiologic factors might modify tumor progression. Further studies are required to refine the molecular characterization of SCRC.

Familial Polyposis Syndromes

Although sporadic polyps in the gastrointestinal tract are common with increasing age, the finding of a large number of polyps raises suspicion for a hereditary polyposis syndrome associated with a germline genetic mutation. Because many of these hereditary polyposis syndromes also confer an increased risk of gastrointestinal and extraintestincal cancers, implicated in approximately 1% of all colorectal cancers, recognition of these syndromes is critical to offer preventive screening measures. A key distinguishing feature is polyp histologic type, ranging from adenomatous, to serrated, to hamartomatous. A clinical diagnosis can be confirmed by genetic testing for a germline mutation in known cancer susceptibility genes, although in many polyposis families, a genetic etiology has not yet been identified. This review covers familial adenomatous polyposis, MUTYH-associated polyposis, polyposis associated with polymerase proofreading, juvenile polyposis syndrome, PTEN hamartoma tumor syndromes, hereditary mixed polyposis syndrome, and serrated polyposis. The figures shows the spectrum of histologic types and genetic etiologies of hereditary polyposis syndromes. Tables list polyposis syndromes, American College of Gastroenterology surveillance guidelines for hereditary polyposis syndromes, diagnostic criteria for juvenile polyposis syndrome, diagnostic criteria for PTEN hamartoma tumor syndrome, and World Health Organization diagnostic criteria for serrated polyposis syndrome. This review contains 1 highly rendered figure, 5 tables, and 172 references Key words: Familial adenomatous polyposis; Polyposis syndromes; Gastrointestinal polyps; Hereditary polyposis syndromes

Abstract 5226: Genomic analysis of pancreatic ductal adenocarcinoma in a patient with MUTYH-associated polyposis

Abstract Biallelic pathogenic germline variants in the DNA repair glycosylase, MUTYH, cause MUTYH-associated polyposis, characterised by an increased susceptibility to colorectal adenomas and carcinomas secondary to defective base excision repair. We report a patient diagnosed with Stage IIB distal pancreatic ductal adenocarcinoma (PDAC) at the age of 45 years. Prior colonoscopy and gastroscopy noted three colonic tubular adenomas and a gastric fundic gland polyp. The patient was consented to whole genome and transcriptome sequencing of the PDAC and matched normal blood DNA through the British Columbia Personalized Onco-Genomics (POG) program. Analysis of germline and somatic variants including single nucleotide variants, copy number determination, loss of heterozygosity detection and mutational signatures was undertaken. Expression fold-changes were calculated against Illumina BodyMap pancreatic tissue averages and compared against The Cancer Genome Atlas PDAC cases. Germline analysis revealed biallelic mutations in the MUTYH gene. In light of this patient's personal and family history of adenomatous colon polyps, clinic-initiated panel testing of 14 cancer susceptibility genes, including MUTYH, via Illumina sequencing with reflex Sanger confirmation revealed the same biallelic MUTYH changes. Analysis of the patient's PDAC revealed a base excision repair pathway signature, demonstrated by an increased frequency of C:G&amp;gt;A:T transversions, consistent with deficient MUTYH activity. This is the first association of germline MUTYH biallelic pathogenic variants with PDAC and provides evidence of the contribution of aberrant MUTYH function to the genomic landscape of a PDAC. Detection of the base excision repair mutational signature may be a sensitive way to screen tumors for aberrant MUTYH function that can reveal potential germline MUTYH-related cancer susceptibility, and allow inference of pathogenicity of detected MUTYH variants, which may have cancer prevention and therapeutic implications. Citation Format: Kasmintan A. Schrader, Carolyn Chu’ng, Eric Zhao, Hui-li Wong, Yaoqing Shen, Martin Jones, Tom Thomson, Howard Lim, Sean Young, Carol Cremin, Robert Holt, Peter Eirew, Joanna Karasinska, Jacquie Schein, Yongjun Zhao, Andy Mungall, Richard Moore, Yussanne Ma, Alexandra Fok, Robyn Roscoe, Stephen Yip, Gillian Mitchell, Aly Karsan, Steven Jones, David Schaeffer, Janessa Laskin, Marco Marra, Daniel Renouf. Genomic analysis of pancreatic ductal adenocarcinoma in a patient with MUTYH-associated polyposis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5226.

Surgical aspects of indications and techniques for adenomatous polyposis variants

Due to the advances in molecular genetic diagnostics of adenomatous polyposis variants, identification of patients with a genetic predisposition and their at risk relatives is becoming increasingly important in clinical practice. Precise knowledge of the specific risk profile is gaining significance especially for surgeons and requires a clinically differentiated approach in order to correctly identify the indications for prophylactic surgery. In this article reference will be made to the technical details of the pouch operation rather than the decision-making process per se, since this has become common knowledge for specialized colorectal surgeons. Besides the more commonly known polyposis syndromes, such as familial adenomatous polyposis (FAP), surgeons should nowadays at least be able to clinically distinguish between attenuated and classical variants of FAP, be aware of MUTYH-associated polyposis (MAP) and also the new polyposis syndrome polymerase proofreading-associated polyposis (PPAP). Surgeons should be familiar with the specific indications and extent of surgery for prophylactic organ removal in the lower gastrointestinal tract in order to be able to competently advise patients.

Clinical Characteristics of Multiple Colorectal Adenoma Patients Without Germline APC or MYH Mutations.

Patients with multiple colorectal adenomas (MCRA) without genetic cause are increasingly being diagnosed. The characteristics and natural history of this condition are not well studied. Twenty-seven patients with MCRA, with cumulatively 10 to 99 colorectal adenomas and without deleterious mutations of APC or MYH genes, were investigated. Results of colonoscopies with a mean follow-up of 4.9 years (range, 0 to 27 y) were evaluated. Findings from esophagogastroduodenoscopy and extracolonic manifestations were assessed. The mean age at polyp diagnosis and MCRA diagnosis was 47.8±13.1 years (range, 21 to 72 y) and 50.4±14.6 years (range, 21 to 72 y), respectively. In 22% of patients another family member had MCRA. At first colonoscopy, the mean number of adenomas was 35.0±35.9 (range, 0 to 99). Serrated polyps were rare. Esophagogastroduodenoscopy revealed 47% of patients had upper tract neoplasia. Patients with upper tract findings were diagnosed with MCRA at significantly younger mean age than those without findings, P<0.05. Eighteen patients (67%) underwent colectomy with a mean time from diagnosis of MCRA of 3.1±1.3 years. After surgery, surveyed patients developed recurrent adenomas in retained colorectum. Nine patients (33%) had extracolonic cancers. MCRA patients have a similar clinicopathologic phenotype to known syndromes of attenuated adenomatous polyposis and the majority have need for colectomy. The management of MCRA patients and families should parallel that of attenuated familial adenomatous polyposis and MUTYH-associated polyposis including surveillance of the upper tract.

An Individual with Both MUTYH-Associated Polyposis and Lynch Syndrome Identified by Multi-Gene Hereditary Cancer Panel Testing: A Case Report.

The utilization of next-generation sequencing technology to interrogate multiple genes simultaneously is being utilized more frequently in hereditary cancer testing. While this has benefits of reducing cost and allowing clinicians to cast a wide net in the elucidation of their patient's cancer, panel testing has the potential to reveal unexpected information. We report on a proband with pathogenic variants resulting in two different hereditary colon cancer syndromes. A 39-year-old male with a history of colon cancer, more than 20 colon polyps and a family history of colon cancer presented for genetic counseling. Testing with a 7-gene high-risk hereditary colon cancer panel identified a homozygous pathogenic variant, c.1187G>A (p.Gly396Asp) in MUTYH, and a likely pathogenic duplication of exon 7 in MSH2. Since this test result, the proband's mother was diagnosed with colon cancer; subsequent genetic testing confirmed she also carries the likely pathogenic duplication in the MSH2 gene. Although the cancer risk in individuals who carry multiple pathogenic variants has not been established for combined biallelic MUTYH-associated polyposis and Lynch syndrome, the identification of multiple pathogenic variants does allow for screening for cancers associated with both syndromes and has implications for cancer risk for family members. In particular, this has significant impact on those who test negative for a known familial pathogenic variant, yet could be still be at risk for cancer due to a second pathogenic variant in a family. More information is needed on the frequency of occurrence of multiple pathogenic variants, as well as the phenotypic spectrum when multiple pathogenic variants are present.

Frequency and Features of Duodenal Adenomas in Patients WithMUTYH-Associated Polyposis.

MUTYH-associated polyposis (MAP) is similar to familial adenomatous polyposis (FAP), in that it increases the risk for duodenal adenomas and cancer. Almost all patients with FAP develop duodenal adenomas and 5% develop duodenal cancer. Little is known about the prevalence of duodenal adenomas and cancer in patients with MAP, but current surveillance recommendations are the same for patients with FAP-they should begin surveillance when they are 25 years old. We aimed to assess the prevalence, extent, and progression of duodenal adenomas in patients with MAP and evaluate upper gastrointestinal tract surveillance recommendations. In a retrospective study, we collected data on all patients (n= 92) with MAP undergoing surveillance esophagogastroduodenoscopy from registries at St Mark's Hospital (London, UK) and the Academic Medical Center (Amsterdam, The Netherlands) from 2002 through 2014. We collected information on adenoma development, age at adenoma detection, interventions, and disease progression. Duodenal adenomas were detected in 31 patients (34%), at a median age of 50 years. When duodenal polyposis first was detected, it was Spigelman stages I or II in 84% of patients; most had few small polyps, without high-grade dysplasia or villous features. Subsequent esophagogastroduodenoscopy evaluation of 18 of these patients found that 14 (78%) had Spigelman stages 0 to II disease (median follow-up period, 7.8 y). Disease progressed in stage in 6 patients, over 9.5 years, because of lesion size or villous features (2 reached stage IV disease). Adenomas were down-staged in 8 patients after biopsy or polypectomy analyses, and were unchanged for 3 patients. In a data analysis from 92 patients with MAP, duodenal polyposis seemed to develop less frequently than in patients with FAP, and developed at a later age. Increasing lesion size and villous change appear to promote adenoma progression, rather than polyp number or dysplasia. It may be time to consider a new staging system for patients with MAP, to better determine disease severity and surveillance strategies.

Exome sequencing identifies potential novel candidate genes in patients with unexplained colorectal adenomatous polyposis.

In up to 30% of patients with colorectal adenomatous polyposis, no germline mutation in the known genes APC, causing familial adenomatous polyposis, MUTYH, causing MUTYH-associated polyposis, and POLE or POLD1, causing Polymerase-Proofreading-associated polyposis can be identified, although a hereditary etiology is likely. To uncover new causative genes, exome sequencing was performed using DNA from leukocytes and a total of 12 colorectal adenomas from seven unrelated patients with unexplained sporadic adenomatous polyposis. For data analysis and variant filtering, an established bioinformatics pipeline including in-house tools was applied. Variants were filtered for rare truncating point mutations and copy-number variants assuming a dominant, recessive, or tumor suppressor model of inheritance. Subsequently, targeted sequence analysis of the most promising candidate genes was performed in a validation cohort of 191 unrelated patients. All relevant variants were validated by Sanger sequencing. The analysis of exome sequencing data resulted in the identification of rare loss-of-function germline mutations in three promising candidate genes (DSC2, PIEZO1, ZSWIM7). In the validation cohort, further variants predicted to be pathogenic were identified in DSC2 and PIEZO1. According to the somatic mutation spectra, the adenomas in this patient cohort follow the classical pathways of colorectal tumorigenesis. The present study identified three candidate genes which might represent rare causes for a predisposition to colorectal adenoma formation. Especially PIEZO1 (FAM38A) and ZSWIM7 (SWS1) warrant further exploration. To evaluate the clinical relevance of these genes, investigation of larger patient cohorts and functional studies are required.

Functional Evaluation of Nine Missense-Type Variants of the Human DNA Glycosylase Enzyme MUTYH in the Japanese Population.

Biallelic germline mutations of MUTYH, the gene encoding DNA glycosylase, cause MUTYH-associated polyposis (MAP), characterized by multiple colorectal adenomas and carcinoma(s). However, a considerable number of MUTYH variants are still functionally uncharacterized. Herein, we report the results of functional evaluation of nine missense-type MUTYH variant proteins in the Japanese population. The DNA glycosylase activity and ability to suppress mutations caused by 8-hydroxyguanine, an oxidized form of guanine, were examined for the nine variants of type 2 MUTYH, a nuclear form of the enzyme, by DNA cleavage activity assay and supF forward mutation assay, respectively. Both activities were severely defective in the p.N210S MUTYH type 2 variant corresponding to p.N238S in the reference MUTYH form and partially defective in p.R219G variant corresponding to p.R247G, but nearly fully retained in seven other variants examined. Our results suggest that p.N238S and p.R247G are likely to be pathogenic alleles for MAP.

Molecular approach to genetic and epigenetic pathogenesis of early-onset colorectal cancer.

Colorectal cancer (CRC) is the third most frequent cancer type and the incidence of this disease is increasing gradually per year in individuals younger than 50 years old. The current knowledge is that early-onset CRC (EOCRC) cases are heterogeneous population that includes both hereditary and sporadic forms of the CRC. Although EOCRC cases have some distinguishing clinical and pathological features than elder age CRC, the molecular mechanism underlying the EOCRC is poorly clarified. Given the significance of CRC in the world of medicine, the present review will focus on the recent knowledge in the molecular basis of genetic and epigenetic mechanism of the hereditary forms of EOCRC, which includes Lynch syndrome, Familial CRC type X, Familial adenomatous polyposis, MutYH-associated polyposis, Juvenile polyposis syndrome, Peutz-Jeghers Syndrome and sporadic forms of EOCRC. Recent findings about molecular genetics and epigenetic basis of EOCRC gave rise to new alternative therapy protocols. Although exact diagnosis of these cases still remains complicated, the present review paves way for better predictions and contributes to more accurate diagnostic and therapeutic strategies into clinical approach.

Mutation analysis of MUTYH in Japanese colorectal adenomatous polyposis patients.

Germline MUTYH mutations were investigated in 14 Japanese colorectal polyposis patients without germ line adenomatous polyposis coli (APC) gene mutations. Three patients had a heterozygous IVS10-2A>G MUTYH mutation. The onset of MUTYH-associated polyposis (MAP) occurs later than that of familial adenomatous polyposis with germline APC mutation. Thus, we compared the carrier frequency of MUTYH IVS10-2A>G heterozygote in the APC mutation negative cases with that in 115 controls over 70 years of age who showed no apparent clinical manifestations of cancer and claimed that they had no history of cancer at the time of enrollment. The frequency of IVS10-2A>G heterozygote in APC germline mutation negative polyposis patients was significantly higher than control subject (p = 0.012, Chi square test). Although the sample size is still too small to conclude, the IVS10-2A>G MUTYH heterozygote might add to the risk of developing germline APC mutation negative polyposis.

Low-level APC mutational mosaicism is the underlying cause in a substantial fraction of unexplained colorectal adenomatous polyposis cases

BackgroundIn 30–50% of patients with colorectal adenomatous polyposis, no germline mutation in the known genes APC, causing familial adenomatous polyposis, MUTYH, causing MUTYH-associated polyposis, or POLE or POLD1, causing polymerase-proofreading-associated...

Adenoma development in familial adenomatous polyposis and MUTYH-associated polyposis: somatic landscape and driver genes.

Familial adenomatous polyposis (FAP) and MUTYH‐associated polyposis (MAP) are inherited disorders associated with multiple colorectal adenomas that lead to a very high risk of colorectal cancer. The somatic mutations that drive adenoma development in these conditions have not been investigated comprehensively. In this study we performed analysis of paired colorectal adenoma and normal tissue DNA from individuals with FAP or MAP, sequencing 14 adenoma whole exomes (eight MAP, six FAP), 55 adenoma targeted exomes (33 MAP, 22 FAP) and germline DNA from each patient, and a further 63 adenomas by capillary sequencing (41 FAP, 22 MAP). With these data we examined the profile of mutated genes, the mutational signatures and the somatic mutation rates, observing significant diversity in the constellations of mutated driver genes in different adenomas, and loss‐of‐function mutations in WTX (9%; p < 9.99e‐06), a gene implicated in regulation of the WNT pathway and p53 acetylation. These data extend our understanding of the early events in colorectal tumourigenesis in the polyposis syndromes. © 2015 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Distinct functional consequences of MUTYH variants associated with colorectal cancer: Damaged DNA affinity, glycosylase activity and interaction with PCNA and Hus1.

MUTYH is a base excision repair (BER) enzyme that prevents mutations in DNA associated with 8-oxoguanine (OG) by catalyzing the removal of adenine from inappropriately formed OG:A base-pairs. Germline mutations in the MUTYH gene are linked to colorectal polyposis and a high risk of colorectal cancer, a syndrome referred to as MUTYH-associated polyposis (MAP). There are over 300 different MUTYH mutations associated with MAP and a large fraction of these gene changes code for missense MUTYH variants. Herein, the adenine glycosylase activity, mismatch recognition properties, and interaction with relevant protein partners of human MUTYH and five MAP variants (R295C, P281L, Q324H, P502L, and R520Q) were examined. P281L MUTYH was found to be severely compromised both in DNA binding and base excision activity, consistent with the location of this variation in the iron-sulfur cluster (FCL) DNA binding motif of MUTYH. Both R295C and R520Q MUTYH were found to have low fractions of active enzyme, compromised affinity for damaged DNA, and reduced rates for adenine excision. In contrast, both Q324H and P502L MUTYH function relatively similarly to WT MUTYH in both binding and glycosylase assays. However, P502L and R520Q exhibited reduced affinity for PCNA (proliferation cell nuclear antigen), consistent with their location in the PCNA-binding motif of MUTYH. Whereas, only Q324H, and not R295C, was found to have reduced affinity for Hus1 of the Rad9-Hus1-Rad1 complex, despite both being localized to the same region implicated for interaction with Hus1. These results underscore the diversity of functional consequences due to MUTYH variants that may impact the progression of MAP.

Mitochondrial variants in MT-CO2 and D-loop instability are involved in MUTYH-associated polyposis.

Mitochondrial DNA alterations have been widely reported in different human tumours, including colorectal carcinoma, but their mutational spectrum and pathogenic role in specific subsets of patients with polyposis syndromes have been poorly investigated. We compared the breadth of somatic variants across the mitochondrial genome of MUTYH-associated polyposis (MAP) patients with homogeneous groups of classical/attenuated familial adenomatous polyposis (FAP/AFAP) and sporadic cases. Overall, we screened 121 adenomas and seven adenocarcinomas and their corresponding germinal controls, for mitochondrial genes with a crucial role in oxidative phosphorylation and translation (MT-CO1, MT-CO2, MT-CO3, MT-TD, MT-TS1, MT-ATP6) as well as a hypervariable sequence (HV-II) within the control region displacement loop (D-loop), a marker of hypermutability and clonal expansion. The sequencing analysis revealed the presence of 17 variants, mostly causing non-synonymous changes in conserved amino acid residues, typically distributed in the MT-CO2 gene of MAP patients (P < 0.0001), who frequently carried the hot spot m.7763G>A variant. Accordingly, D-loop instability was also significantly associated with variants grouped inside the MT-CO2 gene (P = 0.0061). This is the first report showing a locus-specific distribution of mitochondrial DNA alterations in a subtype of colorectal tumourigenesis. In addition, our findings suggest that MT-CO2 variants, representing early molecular events in MAP tumorigenesis, might be a potential prognostic biomarker for the cancer-risk assessment of patients affected by this syndrome. We compared the frequencies of mtDNA variants in MAP vs. FAP/AFAP/sporadic patients. We found a gene-specific (MT-CO2) distribution of mtDNA variants in MAP cases. Most mtDNA variants caused non-synonymous changes in conserved amino acid residues. D-loop instability was significantly associated with variants grouped inside MT-CO2. MT-CO2 variants might be a potential prognostic biomarker in MAP patients.