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

Spectrum of germline cancer susceptibility gene mutations in Turkish colorectal cancer patients: a single center study

Background/aim

Quarter of colorectal cancer patients have a family history and 6% of these comprise hereditary cancer syndromes. For developing national health strategies for genetic screening, it is crucial to determine the spectrum of damaging alterations in causative genes and to describe frequent founder mutations.

Materials and methods

One hundred and thirty six unrelated colorectal cancer cases were investigated. Qiagen large hereditary cancer panel and Hereditary Cancer Solution v1.1 panel were used for sequencing. The sequencing process was performed on the Illumina MiSeq system. The data analyses were performed on QIAGEN Clinical Insight (QCI™) Analyze software and Sophia DDM software.

Results

Of 136 patients, 11 (8%) were found to carry a pathogenic and 2 (1.4%) were found to carry a likely pathogenic mutation. Altogether, 12 different pathogenic and likely pathogenic mutations were detected.

Conclusion

This study is the first study in Turkish colorectal cancer patients using next-generation sequencing. Point mutation screening in the families of patients with mutations will be able to identify individuals at risk in a cost-effective manner.

[MUTYH-associated polyposis: Review and update of the French recommendations established in 2012 under the auspices of the National Cancer Institute (INCa)]

MUTYH-associated polyposis (MUTYH-associated polyposis, MAP) is an autosomal recessive inheritance disorder related to bi-allelic constitutional pathogenic variants of the MUTYH gene which was first described in 2002. In 2011, a group of French experts composed of clinicians and biologists, performed a summary of the available data on this condition and drew up recommendations concerning the indications and the modalities of molecular analysis of the MUTYH gene in index cases and their relatives, as well as the management of affected individuals. In view of recent developments, some recommendations have become obsolete, in particular with regard to the molecular analysis strategy since MUTYH gene has been recently included in a consensus panel of 14 genes predisposing to colorectal cancer. This led us to revise all the points of the previous expertise. We report here the revised version of this work which successively considers the phenotype and the tumor risks associated with this genotype, the differential diagnoses, the indication criteria and the strategy of the molecular analysis and the recommendations for the management of affected individuals. We also discuss the phenotype and the tumor risks associated with mono-allelic pathogenic variants of MUTYH gene.

c.1227_1228dupGG (p.Glu410Glyfs), a frequent variant in Tunisian patients with MUTYH associated polyposis

INTRODUCTION

Familial adenomatous polyposis (FAP) is an autosomal dominant-inherited disease caused by germline variants in the APC gene. It is characterized by the development of hundreds to thousands of adenomatous polyps in colon and rectum. Recently, biallelic germline variants in the base excision repair (BER) gene: MUTYH have been identified in patients with attenuated FAP and/or negative APC result. It can be responsible for an autosomal recessive inherited colorectal cancer syndrome (MAP syndrome: MUTYH-associated polyposis).

OBJECTIVE

The aim of this study was to evaluate germline variants of MUTYH gene in Tunisian patients with attenuated FAP.

METHODS

thirteen unrelated patients from Tunisia with attenuated FAP were screened for MUTYH germline variants. Direct sequencing was performed to identify point variants in this gene.

RESULTS

A Biallelic MUTYH germline variant were found in all patients and showed an attenuated polyposis phenotype almost of them without extra-colic manifestations: The known pathogenic frameshift variant c.1227_1228dupGG (p. Glu410Glyfs) was found, in homozygous state, in 13 index patients.

CONCLUSION

Patients with attenuated familial adenomatous polyposis (<=100) and no obvious vertical transmission of the disease should be considered for MUTYH gene testing.

Molecular basis of familial adenomatous polyposis in the southeast of Brazil: identification of six novel mutations

BACKGROUND

The goal of this study was to screen point mutations and deletions in APC and MUTYH genes in patients suspected of familial adenomatous polyposis (FAP) in a Brazilian cohort.

METHODS

We used high-resolution melting, Sanger direct sequencing and multiplex ligation-dependent probe association (MLPA) assays to identify point mutations, and large genomic variations within the coding regions of APC and MUTYH genes.

RESULTS

We identified 19 causative mutations in 40 Brazilian patients from 20 different families. Four novel mutations were identified in the APC gene and two in the MUTYH gene. We also found a high intra- and inter-familial diversity regarding extracolonic manifestations, and gastric polyps were the most common manifestation found in our cohort.

CONCLUSION

We believe that the FAP mutational spectrum can be population-specific and screening FAP patients in different populations can improve pre-clinical diagnosis and improve clinical conduct.

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.

The genetic basis of familial adenomatous polyposis and its implications for clinical practice and risk management

Familial adenomatous polyposis (FAP) is an inherited disorder that represents the most common gastrointestinal polyposis syndrome. Germline mutations in the APC gene were initially identified as responsible for FAP, and later, several studies have also implicated the MUTYH gene as responsible for this disease, usually referred to as MUTYH-associated polyposis (MAP). FAP and MAP are characterized by the early onset of multiple adenomatous colorectal polyps, a high lifetime risk of colorectal cancer (CRC), and in some patients the development of extracolonic manifestations. The goal of colorectal management in these patients is to prevent CRC mortality through endoscopic and surgical approaches. Individuals with FAP and their relatives should receive appropriate genetic counseling and join surveillance programs when indicated. This review is focused on the description of the main clinical and genetic aspects of FAP associated with germline APC mutations and MAP.

Germline CDKN2A mutations in Brazilian patients of hereditary cutaneous melanoma

Approximately 10 % of all cutaneous melanoma cases occur in a familial context. The major susceptibility gene for familial melanoma is CDKN2A. In Latin America, genetic studies investigating melanoma predisposition are scarce. The aim of this work was to investigate germline CDKN2A point mutations and genomic rearrangements in a cohort of 59 Brazilian melanoma-prone patients. Screening of CDKN2A alterations was performed by sequencing and multiplex ligation probe amplification. Germline CDKN2A mutations affecting p16(INK4a) were detected in 8 unrelated probands (13.6 %), including 7 familial cases and one patient with multiple melanomas; 4 out of 8 mutation carriers met the criteria for familial melanoma and had multiple primary lesions. Although this study adds to the literature on melanoma susceptibility in Latin America, it is limited by the small size of the cohort. Our findings suggest that stringent inclusion criteria led to a substantially increased rate of CDKN2A mutation detection. This consideration should be taken into account when referring patients for genetic screening in a setting of limited budget, such as in developing countries.

MUTYH-associated colorectal cancer and adenomatous polyposis

MUTYH-associated polyposis (MAP) was first described in 2002. MUTYH is a component of a base excision repair system that protects the genomic information from oxidative damage. When the MUTYH gene product is impaired by bi-allelic germline mutation, it leads to the mutation of cancer-related genes, such as the APC and/or the KRAS genes, via G to T transversion. MAP is a hereditary colorectal cancer syndrome inherited in an autosomal-recessive fashion. The clinical features of MAP include the presence of 10-100 adenomatous polyps in the colon, and early onset of colorectal cancer. Ethnic and geographical differences in the pattern of the MUTYH gene mutations have been suggested. In Caucasian patients, c.536A>G (Y179C) and c.1187G>A (G396D) mutations are frequently detected. In the Asian population, Y179C and G396D are uncommon, whereas other variants are suggested to be the major causes of MAP. We herein review the literature on MUTYH-associated colorectal cancer and adenomatous polyposis.

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.

MUTYH the base excision repair gene family member associated with colorectal cancer polyposis

COLORECTAL CANCER IS CLASSIFIED IN TO THREE FORMS

sporadic (70-75%), familial (20-25%) and hereditary (5-10%). hereditary colorectal cancer syndromes classified into two different subtypes: polyposis and non polyposis. Familial Adenomatous polyposis (FAP; OMIM #175100) is the most common polyposis syndrome, account for <1% of colorectal cancer incidence and characterized by germline mutations in the Adenomatous polyposis coli (APC, 5q21- q22; OMIM #175100). FAP is a dominant cancer predisposing syndrome which 20-25% cases are de novo. There is also another polyposis syndrome; MUTYH associated polyposis (MAP, OMIM 608456) which it is caused by mutation in human Mut Y homologue MUTYH (MUTYH; OMIM 604933) and it is associated with multiple (15-100) colonic adenomas. In this paper we discuss MUTYH mechanism as an important member of Base Excision Repair (BER) family and its important role in polyposis condition.

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.