Germline APC variants in patients with multiple colorectal adenomas, with evidence for the particular importance of E1317Q

Gene-specific ACMG/AMP classification criteria for germline APC variants: Recommendations from the ClinGen InSiGHT Hereditary Colorectal Cancer/Polyposis Variant Curation Expert Panel

PURPOSE

The Hereditary Colorectal Cancer/Polyposis Variant Curation Expert Panel (VCEP) was established by the International Society for Gastrointestinal Hereditary Tumours and the Clinical Genome Resource, who set out to develop recommendations for the interpretation of germline APC variants underlying Familial Adenomatous Polyposis, the most frequent hereditary polyposis syndrome.

METHODS

Through a rigorous process of database analysis, literature review, and expert elicitation, the APC VCEP derived gene-specific modifications to the ACMG/AMP (American College of Medical Genetics and Genomics and Association for Molecular Pathology) variant classification guidelines and validated such criteria through the pilot classification of 58 variants.

RESULTS

The APC-specific criteria represented gene- and disease-informed specifications, including a quantitative approach to allele frequency thresholds, a stepwise decision tool for truncating variants, and semiquantitative evaluations of experimental and clinical data. Using the APC-specific criteria, 47% (27/58) of pilot variants were reclassified including 14 previous variants of uncertain significance (VUS).

CONCLUSION

The APC-specific ACMG/AMP criteria preserved the classification of well-characterized variants on ClinVar while substantially reducing the number of VUS by 56% (14/25). Moving forward, the APC VCEP will continue to interpret prioritized lists of VUS, the results of which will represent the most authoritative variant classification for widespread clinical use.

Position statement of the International Society for Gastrointestinal Hereditary Tumours (InSiGHT) on APC I1307K and cancer risk

While constitutional pathogenic variants in the APC gene cause familial adenomatous polyposis, APC c.3920T>A; p.Ile1307Lys (I1307K) has been associated with a moderate increased risk of colorectal cancer (CRC), particularly in individuals of Ashkenazi Jewish descent. However, published data include relatively small sample sizes, generating inconclusive results regarding cancer risk, particularly in non-Ashkenazi populations. This has led to different country/continental-specific guidelines regarding genetic testing, clinical management and surveillance recommendations for I1307K. A multidisciplinary international expert group endorsed by the International Society for Gastrointestinal Hereditary Tumours (InSiGHT), has generated a position statement on the APC I1307K allele and its association with cancer predisposition. Based on a systematic review and meta-analysis of the evidence published, the aim of this document is to summarise the prevalence of the APC I1307K allele and analysed the evidence of the associated cancer risk in different populations. Here we provide recommendations on the laboratory classification of the variant, define the role of predictive testing for I1307K, suggest recommendations for cancer screening in I1307K heterozygous and homozygous individuals and identify knowledge gaps to be addressed in future research studies. Briefly, I1307K, classified as pathogenic, low penetrance, is a risk factor for CRC in individuals of Ashkenazi Jewish origin and should be tested in this population, offering carriers specific clinical surveillance. There is not enough evidence to support an increased risk of cancer in other populations/subpopulations. Therefore, until/unless future evidence indicates otherwise, individuals of non-Ashkenazi Jewish descent harbouring I1307K should be enrolled in national CRC screening programmes for average-risk individuals.

The impact of APC polymorphisms on the transition from polyps to colorectal cancer (CRC)

OBJECTIVE

The purpose of this study was to investigate the function of APC polymorphisms (D1822V and E1317Q) on the transition from polyps to colorectal cancer (CRC).

METHODS

259 patients with polyps were included in the study. APC polymorphisms were genotyped via polymerase chain reaction (PCR) and subsequent sequencing. χ² test was performed to analyze the relationship of APC polymorphisms or CRC occurrence with clinical features. COX regression was used to find out risk factors for CRC. Hazard ratio (HR) and 95% confidence interval (CI) represented the risk of CRC.

RESULTS

Clinical information on sex, regular physical activity, smoking history, alcohol use and polyps types was recorded. Neither D1822V nor E1317Q polymorphism was associated with these factors. In following analysis, we found significant difference in the frequency of males between CRC and non-CRC patients (87.4% vs. 58.7%, P < 0.001). Distinct difference in the distribution of D1822V polymorphism was also observed between CRC and non-CRC patients (P = 0.001). In COX analysis, sex was identified as a risk factor for transition from polyps to CRC (HR = 2.442, 95%CI = 1.281-4.654). D1822V polymorphism tended to inhibit the transition process (HR = 0.286, 95%CI = 0.170-0.480). However, E1317Q seemed to have no significant effect on this process (HR = 1.042, 95%CI = 0.676-1.606).

CONCLUSION

In a word, APC D1822V polymorphism has strong effect on the transition from polyps to CRC.

Targeted next generation sequencing reveals a common genetic pathway for colorectal cancers with chromosomal instability and those with microsatellite and chromosome stability

INTRODUCTION

Microsatellite stable sporadic colorectal cancers (CRCs) can be classified as either tumours with chromosomal instability (CIN+) or tumours that are 'Microsatellite and Chromosomal Stable' (MACS). The CIN + tumours are aneuploid whilst MACS are near-diploid; little else is known about their differences. We compared the mutation profiles of CIN + and MACS CRCs.

METHOD

Targeted Next Generation Sequencing for mutation in 26 driver genes (TruSight-26 kit) was undertaken in 46 CIN + and 35 MACSCRCs. Tumours were compared for mutation frequency, allelic imbalance and clonal heterogeneity.

RESULTS

Mutations were detected in 58% genes and, overall, mutation in driver genes was at expected frequencies. Comparison of classes revealed similar mutation frequencies in most genes and allelic imbalance atAPC and TP53. Differences were seen in mutation frequency in KRAS (41% CIN+ vs 68% MACS, p = 0.015) and GNAS (0% CIN+ vs 12% MACS, p = 0.032). Twenty percent CIN + CRCs harboured mutations only in TP53 - a profile not seen in the MACS tumours (p = 0.009). None of the differences were significant after multiple testing corrections.

CONCLUSIONS

The mutation profiles of CIN and MACS CRCs are similar. The events allowing aneuploidy (or forcing retention of diploidy) remain unknown.

Association of APC I1307K and E1317Q polymorphisms with colorectal cancer among Egyptian subjects

Colorectal cancer is a multifactorial disease that involves both environmental and genetic factors. The gene encoding adenomatous polyposis coli (APC) has been reported to be associated with colorectal cancer (CRC) risk in several ethnic populations. The aim of this work is to assess the association of the APC I1307K and E1317Q polymorphisms with CRC risk among Egyptian subjects. This study included 120 unrelated CRC Egyptian patients who were compared to 100 healthy controls from the same locality. For all subjects, DNA was genotyped for APC I1307K and E1317Q polymorphisms using the PCR-ARMS technique. The frequency of APC I1307K carrier (TA+AA genotypes) was noted to be significantly higher among cases with CRC compared to controls (18.3 vs. 9.0 %, OR 2.58, 95 % CI 1.09-6.09, p = 0.03). Also the frequency of the APC I1307K A allele was significantly higher among cases compared to controls (10.4 vs. 4.5 %, OR 2.47; 95 % CI 1.12-5.42, p = 0.03). On the contrast, the frequencies of APC E1317Q GC genotype and C allele showed no significant difference among CRC patients compared to controls (3.3 vs. 2.0 %, OR 1.69; 95 % CI 0.30-9.42, p = 0.69 and 2.1 vs. 1.0 %, OR 2.11; 95 % CI 0.40-10.97, p = 0.46, respectively). Cases of the APC I1307K and E1317Q carriers (TA+AA and GC) showed no significant difference compared to those with I1307K and E1317Q non-carriers (TT and GG) regarding their clinical and laboratory markers. APC I1307K variant was associated with an increased risk of CRC among Egyptian subjects.

Detection of a Tumor Suppressor Gene Variant Predisposing to Colorectal Cancer in an 18th Century Hungarian Mummy

Mutations of the Adenomatous polyposis coli (APC) gene are common and strongly associated with the development of colorectal adenomas and carcinomas. While extensively studied in modern populations, reports on visceral tumors in ancient populations are scarce. To the best of our knowledge, genetic characterization of mutations associated with colorectal cancer in ancient specimens has not yet been described. In this study we have sequenced hotspots for mutations in the APC gene isolated from 18th century naturally preserved human Hungarian mummies. While wild type APC sequences were found in two mummies, we discovered the E1317Q missense mutation, known to be a colorectal cancer predisposing mutation, in a large intestine tissue of an 18th century mummy. Our data suggests that this genetic predisposition to cancer already existed in the pre-industrialization era. This study calls for similar investigations of ancient specimens from different periods and geographical locations to be conducted and shared for the purpose of obtaining a larger scale analysis that will shed light on past cancer epidemiology and on cancer evolution.

Colorectal tumors from APC*I1307K carriers principally harbor somatic APC mutations outside the A8 tract

Purpose

APC*I1307K (c.3920T>A) is an inherited variant associated with colorectal tumour risk found almost exclusively in those of Ashkenazi Jewish ancestry. A single nucleotide substitution creates an oligo-adenine tract (A8) that appears to be inherently prone to further mis-pairing and slippage. The reported multiple tumor phenotype of carriers is not easily reconciled with molecular and population genetics data. We postulated that some c.3920T>A carriers with multiple adenomas have other unidentified APC germ line or somatic mutations.

Methods

DNA from 82 colonic tumours and accompanying normal tissue collected from 29 carriers with multiple colorectal tumors was directly sequenced between codons 716 and 1604. We also assessed APC gene loss of heterozygosity.

Results

One patient (3.4%) was found to have an additional APC germ line mutation. Twenty-five of the tumours showed no significant somatic molecular change, 36 showed one change, 20 showed two, and one tumour showed more than 2 changes. Our data suggest a correlation between advancing histology and fewer beta-catenin binding sites remaining in the mutant proteins.

Conclusions

There were no other common germ line variants identified within the region of the APC gene examined, suggesting that any effect from this region on tumour production is attributable to the c.3920T>A allele. Our findings further suggest the only somatic genetic change clearly attributable to the c.3920T>A mutation is the c.3924_3925insA.

APC germline mutations in families with familial adenomatous polyposis

Adenomatous polyposis coli (APC) germline mutations are responsible for the occurrence of familial adenomatous polyposis (FAP). Somatic mutations lead to malignant transformation of adenomas. In this context, considering the significance of APC germline mutations in FAP, we aimed to identify APC germline mutations. In the present study, 20 FAP patients were enrolled. The determination of APC germline mutations was performed using sequencing, and the mutations were compared with clinical markers (gender, age at diagnosis, smoking habits, TNM stage, Astler‑Coller stage, degree of differentiation of adenocarcinoma). The data were compared using the SPSS program, with the Fisher's exact test and χ2 test, considering α=0.05. According to the main results in our sample, 16 alleles with deleterious mutations (80% of the patients) were identified while 7 (35%) patients had no deleterious mutations. There was a predominance of nonsense (45% of the patients) and frameshift (20% of the patients) mutations. There was no statistical significance between the APC germline mutations identified and the clinical variables considered in our study. Only TNM stage was associated with the presence of deleterious mutations. Patients with deleterious mutations had an OR, 0.086 (IC=0.001-0.984); TNM stage I+II in comparison with III+IV, when compared with the patients with no deleterious mutations identified. In this context, as a conclusion, we demonstrated the molecular heterogeneity of APC germline mutations in FAP and the difficulty to perform molecular diagnostics in a Brazilian population, considering the admixed population analyzed.

APC polymorphisms and the risk of colorectal neoplasia: a HuGE review and meta-analysis

Adenomatous polyposis coli gene (APC) polymorphisms may influence the risk for colorectal neoplasia. However, results thus far have been inconclusive. We performed a systematic literature search of the Medline, Embase, Cochrane Collaboration, and HuGE databases and reviewed the references of pertinent articles through May 2012. Odds ratios with 95% confidence intervals were used to estimate the association between 3 APC polymorphisms (D1822V, E1317Q, and I1307K) and colorectal neoplasia. In total, 40 studies from 1997 to 2010 were included in this meta-analysis, and individuals with the D1822V variant homozygote VV genotype had a slight decrease in the risk for colorectal neoplasia compared with the wild-type homozygote DD genotype (pooled odds ratio = 0.87, 95% confidence interval: 0.77, 0.99). There was a small association between the APC E1317Q polymorphism and a risk for colorectal neoplasia (variant vs. wild-type: pooled odds ratio = 1.41, 95% confidence interval: 1.14, 1.76), particularly for colorectal adenomas (variant vs. wild-type: odds ratio = 2.89, 95% confidence interval: 1.83, 4.56). Compared with those who carried the wild-type I1307K, Ashkenazi Jews who carried the I1307K variant were at a significantly increased risk for colorectal neoplasia, with a pooled odds ratio of 2.17 (95% confidence interval: 1.64, 2.86). Our study suggests that APC is a candidate gene for colorectal neoplasia susceptibility.

Role of rare variants in undetermined multiple adenomatous polyposis and early-onset colorectal cancer

Some 15-20% of multiple adenomatous polyposis have no genetic explanation and 20-30% of colorectal cancer (CRC) cases are thought to be due to inherited multifactorial causes. Accumulation of deleterious effects of low-frequency dominant and independently acting variants may be a partial explanation for such patients. The aim of this study was to type a selection of rare and low-frequency variants (<5%) to elucidate their role in CRC susceptibility. A total of 1181 subjects were included (866 controls; 315 cases). Cases comprised UK (n=184) and French (n=131) patients with MAP (n=187) or early-onset CRC (n=128). Seventy variants in 17 genes were examined in cases and controls. The effect of the variant effect on protein function was investigated in silico. Out of the 70 variants typed, 36 (51%) were tested for association. Twenty-one variants were rare (minor allele frequency (MAF) <1%). Four rare variants were found to have a significantly higher MAF in cases (EXO1-12, MLH1-1, CTNNB1-1 and BRCA2-37, P<0.05) than in controls. Pooling all rare variants with a MAF <0.5% showed an excess risk in cases (odds ratio=3.2; 95% confidence interval=1.1-9.5; P=0.04). Rare variants are important risk factors in CRC and, as such, should be systematically assayed alongside common variation in the search for the genetic basis of complex diseases.

SEQCHIP: a powerful method to integrate sequence and genotype data for the detection of rare variant associations

MOTIVATION

Next-generation sequencing greatly increases the capacity to detect rare-variant complex-trait associations. However, it is still expensive to sequence a large number of samples and therefore often small datasets are used. Given cost constraints, a potentially more powerful two-step strategy is to sequence a subset of the sample to discover variants, and genotype the identified variants in the remaining sample. If only cases are sequenced, directly combining sequence and genotype data will lead to inflated type-I errors in rare-variant association analysis. Although several methods have been developed to correct for the bias, they are either underpowered or theoretically invalid. We proposed a new method SEQCHIP to integrate genotype and sequence data, which can be used with most existing rare-variant tests.

RESULTS

It is demonstrated using both simulated and real datasets that the SEQCHIP method has controlled type-I errors, and is substantially more powerful than all other currently available methods.

AVAILABILITY

SEQCHIP is implemented in an R-Package and is available at http://linkage.rockefeller.edu/suzanne/seqchip/Seqchip.html.

A survey of APC mutations in Quebec

This is an 11-year survey of molecular analysis of APC germline mutations for the province of Quebec done at the Molecular Pathology Unit of the Jewish General Hospital which offers genetic testing for hereditary forms of colorectal cancer for the whole of Quebec province. We report on 47 unique mutations seen in 66 families affected with familial adenomatous polyposis. Of these unique mutations, 60% are short indels, 28% are point mutations, and 6% are whole exon deletions. The absence of founder mutations and the variety of mutations encountered reinforce the value of RNA-based testing and the need for gene dosage techniques such as multiplex ligation-dependent probe amplification.

Familial colorectal cancer type X syndrome: two distinct molecular entities?

In a fraction of families fulfilling the Amsterdam criteria for hereditary non-polyposis colorectal cancer, colorectal cancers are microsatellite stable and DNA mismatch repair gene (MMR) mutations are not found. These families were designated as familial colorectal cancer type X (FCCTX). We aimed to characterise a group of FCCTX families defined by the Amsterdam criteria and MSS tumours at clinical and molecular level. Twenty-four tumours from 15 FCCTX families were analysed for loss of known tumour suppressor gene (TSG) loci (APC, TP53, SMAD4 and DCC), MGMT and MMR genes promoter methylation, and also APC and KRAS somatic mutations. FCCTX families presented specific clinical features: absence of endometrial tumours, high adenoma/carcinoma ratio (1.91) and prevalence of rectal cancers (13/27, 48%). New molecular features were found: the majority of FCCTX tumours (13/18; 72%) presented TSG loss. TSG loss positive tumours presented frequent APC and KRAS somatic mutations and MGMT methylation [10/13 (77%), 7/13 (54%) and 6/11 (54%), respectively]. In TSG loss negative tumours (5/18; 28%), the same molecular events were found in 2/5 (40%), 2/5 (40%) and 1/3 (33%) tumours, respectively. Transition mutations in KRAS were more frequent among MGMT methylated tumours than in unmethylated [5/8 (63%) vs. 1/10 (10%), P = 0.03]. Although sharing similar clinical features, at least two different molecular entities should exist among FCCTX families, one whose tumours present frequent TSG loss, APC and KRAS somatic mutations, and MGMT promoter methylation, and a second, lesser predominant, with no evidence of TSG loss and rarely presenting promoter methylation.

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.

Cyclin D1 rare variants in UK multiple adenoma and early-onset colorectal cancer patients

We examined the influence that rare variants and low-frequency polymorphisms in the cancer candidate gene CCND1 have on the development of multiple intestinal adenomas and the early onset of colorectal cancer. Individuals with <100 multiple polyps and patients with colorectal cancer diagnosed before 50 years of age were recruited in UK, and screened for sequence changes in the coding and regulatory regions of CCND1. A set of about 800 UK control individuals was genotyped for the variants discovered in the cases. Variants in the promoter, intron-exon boundaries and untranslated regions of the CCND1 gene had higher frequencies in cases than in controls. Five of these variants were typed in a set of French multiple adenoma and early-onset patients, who also showed higher allele frequencies than UK controls. When pooled together, variants with frequencies lower than 1% conferred an increased risk of disease that was significant in the multiple adenoma group (odds ratio (OR) 2.2; 95% confidence interval, 1.1-4.4; P = 0.03). Most variants had a putative functional effect when assessed in silico. We conclude that rare variants of CCND1 are risk factors for colorectal cancer, with considerably larger effects than common polymorphisms, and as such should be systematically evaluated in susceptibility studies.

Inactivation of the APC gene is constant in adrenocortical tumors from patients with familial adenomatous polyposis but not frequent in sporadic adrenocortical cancers

PURPOSE

In adrenocortical tumors (ACT), Wnt/β-catenin pathway activation can be explained by β-catenin somatic mutations only in a subset of tumors. ACT is observed in patients with familial adenomatous polyposis (FAP) with germline APC mutations, as well as in patients with Beckwith-Wiedemann syndrome with Wilms' tumors reported to have WTX somatic mutations. Both APC and WTX are involved in Wnt/β-catenin pathway regulation and may play a role in ACT tumorigenesis. The aim of this study was to report if APC and WTX may be associated with FAP-associated and sporadic ACT.

EXPERIMENTAL DESIGN

ACTs from patients with FAP and sporadic adrenocortical carcinomas (ACC) with abnormal β-catenin localization on immunohistochemistry but no somatic β-catenin mutations were studied. APC was analyzed by denaturing high-performance liquid chromatography followed by direct sequencing and by multiplex ligation-dependent probe amplification when allelic loss was suspected. WTX was studied by direct sequencing.

RESULTS

Four ACTs were observed in three patients with FAP and were ACC, adrenocortical adenoma, and bilateral macronodular adrenocortical hyperplasia, all with abnormal β-catenin localization. Biallelic inactivation of APC was strongly suggested by the simultaneous existence of somatic and germline alterations in all ACTs. In the 20 sporadic ACCs, a silent heterozygous somatic mutation as well as a rare heterozygous polymorphism in APC was found. No WTX mutations were observed.

CONCLUSIONS

ACT should be considered a FAP tumor. Biallelic APC inactivation mediates activation of the Wnt/β-catenin pathway in the ACTs of patients with FAP. In contrast, APC and WTX genetic alterations do not play a significant role in sporadic ACC.

The APC Variant p.Glu1317Gln predisposes to colorectal adenomas by a novel mechanism of relaxing the target for tumorigenic somatic APC mutations

Multiple rare nonsynonymous variants in APC predispose to colorectal adenomas. The mechanisms through which such variants act have been unclear, but it has been proposed that a specific ("just-right") level of beta-catenin signaling is required for colorectal tumorigenesis. This appears to be mediated by selection for APC genotypes that retain one, or rarely two, 20 amino acid beta-catenin downregulating repeats (20AARs). We investigated the mechanism through which the variant p.Glu1317Gln (c.3949G>C) contributes to colorectal tumorigenesis. We compared the patterns of somatic APC mutations in tumors from patients with attenuated familial adenomatous polyposis (AFAP) who did, or did not, coinherit p.Glu1317Gln with their AFAP-causing APC mutations. Only 8.2% (4/49) of tumors carrying p.Glu1317Gln had somatic mutations predicted to result in mutant polypeptides retaining a single 20AAR, compared to 62.1% (36/58) of those which did not carry this variant (P=5.64 x 10(-9)). Furthermore, tumors with p.Glu1317Gln often carried somatic mutations that were unusually early or late (downstream of the second 20AAR) in the APC open reading frame. These data support a novel mechanism in which p.Glu1317Gln in combination with other weak mutant APC alleles (generating polypepetides with zero, two, or three 20AARs) can provide the necessary growth advantage for colorectal tumorigenesis.

Analysis of candidate genes in occurrence and growth of colorectal adenomas

Predisposition to sporadic colorectal tumours is influenced by genes with minor phenotypic effects. A case-control study was set up on 295 patients treated for a large adenoma matched with polyp-free individuals on gender, age, and geographic origin in a 1 : 2 proportion. A second group of 302 patients treated for a small adenoma was also characterized to distinguish effects on adenoma occurrence and growth. We focussed the study on 38 single nucleotide polymorphisms (SNPs) encompassing 14 genes involved in colorectal carcinogenesis. Effect of SNPs was tested using unconditional logistic regression. Comparisons were made for haplotypes within a given gene and for biologically relevant genes combinations using the combination test. The APC p.Glu1317Gly variant appeared to influence the adenoma growth (P = .04, exact test) but not its occurrence. This result needs to be replicated and genome-wide association studies may be necessary to fully identify low-penetrance alleles involved in early stages of colorectal tumorigenesis.

APC, MYH, and the correlation genotype-phenotype in colorectal polyposis

BACKGROUND

Familial adenomatous polyposis (FAP) has been divided into two entities: classical (CFAP) and attenuated (AFAP). With the discovery of MYH associated polyposis (MAP) syndrome, the clinical differences have become unclear. The aim of our study was to investigate patients with polyposis treated in our institution for a correlation between genotype and phenotype.

METHODS

Between 1978 and 2007, 515 patients were followed. Four groups were identified: AFAP, CFAP, MAP, and no-mutation patients. Clinical, surgical, histological, and genetic data of patients were collected and compared. Two ranges of mutations responsible for AFAP were used.

RESULTS

Patient breakdown was CFAP patients (n = 322/294), AFAP patients (n = 13/41), MYH patients (n = 17) and no-mut patients (n = 32). Patients not tested for APC mutation (n = 131) were excluded. Genotype/phenotype evaluation showed no difference in the number or location of polyps, age at colectomy, presence of cancer, or duodenal polyps. Major differences were found for MYH patients: later age at diagnosis, more cancers, fewer polyps, and more located in the right part of the colon. For phenotype/genotype correlation, patients aged more than 35 years at the time of colectomy and with fewer than 100 polyps had significantly more mutation found on MYH.

CONCLUSIONS

This two-way analysis did not show any correlation that might help to identify a subgroup of patients with APC mutation that may be considered attenuated. It is more likely that the MAP syndrome is the real AFAP.

Hyperplastic polyps and sessile serrated adenomas as a phenotypic expression of MYH-associated polyposis

BACKGROUND & AIMS

MYH-associated polyposis (MAP) is a disorder caused by a bi-allelic germline MYH mutation, characterized by multiple colorectal adenomas. These adenomas typically harbor G:C-->T:A transversions in the APC and K-ras genes caused by MYH deficiency. Occasional hyperplastic polyps (HPs) have been described in MAP patients but a causal relationship has never been investigated. We examined the presence of HPs and sessile serrated adenomas (SSAs) in 17 MAP patients and studied the occurrence of G:C-->T:A transversions in the APC and K-ras gene in these polyps.

METHODS

MAP patients were analyzed for the presence of HPs/SSAs. APC-mutation cluster region and K-ras codon 12 mutation analysis was performed in adenomas (n = 22), HPs (n = 63), and SSAs (n = 10) from these patients and from a control group of sporadic adenomas (n = 17), HPs (n = 24), and SSAs (n = 17).

RESULTS

HPs/SSAs were detected in 8 of 17 (47%) MAP patients, of whom 3 (18%) met the criteria for hyperplastic polyposis syndrome. APC mutations were detected only in adenomas and comprised exclusively G:C-->T:A transversions. K-ras mutations were detected in 51 of 73 (70%) HPs/SSAs in MAP patients, compared with 7 of 41 (17%) sporadic HPs/SSAs in the control group (P < .0001). In HPs/SSAs, 48 of 51 (94%) K-ras mutations showed G:C-->T:A transversions, compared with 2 of 7 (29%) sporadic HPs/SSAs in the control group (P < .0001).

CONCLUSIONS

HPs and SSAs are a common finding in MAP patients. The detection of almost exclusively G:C-->T:A transversions in the K-ras gene of HPs/SSAs strongly suggests that these polyps are related causally to MYH deficiency. This implies that distinct pathways, that is, APC-gene related in adenomas and nonrelated in HPS/SSAs, appear to be operational in MAP.

Missense polymorphisms in the adenomatous polyposis coli gene and colorectal cancer risk

PURPOSE

Whereas truncating germline mutations of the adenomatous polyposis coli (APC) gene give rise to familial adenomatous polyposis, missense polymorphisms of APC may confer a weaker risk for colorectal cancer.

METHODS

We sequenced the entire open reading frame of the APC gene and tested for two common MYH mutations in a population-based series of patients with colorectal cancer and 5 to 99 adenomas. Missense adenomatous polyposis coli alterations identified in this colorectal cancer multiple-polyp population were analyzed in a population-based series of patients with colorectal cancer and healthy control subjects.

RESULTS

Germline APC or mutY human homologue (MYH) alterations were identified in 16 of 39 colorectal cancer-multiple polyp patients. Four missense APC gene alterations (S130G, E1317Q, D1822V, G2502S) were observed in 13 individuals and 3 additional patients carried presumed pathogenic (APC Y94X, biallelic MYH Y165C and heterozygous MYH G382D) mutations. When independently assessed in 971 patients with colorectal cancer and 954 healthy control subjects, none of the identified missense APC alterations conferred a significantly increased risk for colorectal cancer, odds ratio (95 percent confidence intervals): S130G = 3.1 (0.29-32.25), E1317Q = 1.08 (0.59-2.74), G2502S = 1 (0.65-1.63), D1822V (heterozygous) = 0.79 (0.64-0.98), D1822V (homozygous) = 0.82 (0.63-1.27).

CONCLUSIONS

Germline missense APC alterations observed in 33 percent of patients with multiple colorectal neoplasms seemed to play a limited role in colorectal cancer risk when independently assessed by a population-based, case-control analysis.

Multiple rare nonsynonymous variants in the adenomatous polyposis coli gene predispose to colorectal adenomas

It has been proposed that multiple rare variants in numerous genes collectively account for a substantial proportion of multifactorial inherited predisposition to a variety of diseases, including colorectal adenomas (CRA). We have studied this hypothesis by sequencing the adenomatous polyposis coli (APC) gene in 691 unrelated North American patients with CRAs and 969 matched healthy controls. Rare inherited nonsynonymous variants of APC were significantly overrepresented in patients who did not carry conventional pathogenic mutations in the APC or MutY homologue genes [non-familial adenomatous polyposis (FAP) non-MUTYH-associated polyposis (MAP) patients; 81 of 480, 16.9%] compared with patients with FAP or MAP (20 of 211, 9.5%, P = 0.0113), and this overrepresentation was highest in those non-FAP non-MAP patients with 11 to 99 CRAs (30 of 161, 18.6%, P = 0.0103). Furthermore, significantly more non-FAP non-MAP patients carried rare nonsynonymous variants in the functionally important beta-catenin down-regulating domain compared with healthy controls (32 of 480 versus 37 of 969, P = 0.0166). In silico analyses predicted that approximately 46% of the 61 different variants identified were likely to affect function, and upon testing, 7 of 16 nonsynonymous variants were shown to alter beta-catenin-regulated transcription in vitro. These data suggest that multiple rare nonsynonymous variants in APC play a significant role in predisposing to CRAs.

American founder mutation for attenuated familial adenomatous polyposis

BACKGROUND & AIMS

Specific mutations in the adenomatous polyposis coli (APC) gene can lead to an attenuated form of familial adenomatous polyposis (AFAP). Although AFAP mutation carriers have a 69% risk of colorectal cancer by age 80, clinical recognition remains a challenge in some cases because they present with few colonic adenomas and are difficult to distinguish clinically from patients with sporadic polyps.

METHODS

Family relationships were established using family history reports, the Utah Population Database, and the public records of the Mormon Church. Genetic analysis of representative family members was performed using a 10,000 single nucleotide polymorphism array platform. Colonoscopy data were available on 120 individuals with the AFAP mutation.

RESULTS

Two large AFAP kindreds with the identical APC disease-causing mutation (c.426_427delAT) were linked to a founding couple who came to America from England around 1630. Genetic analysis showed that the 2 families share a conserved haplotype of 7.17 Mbp surrounding the mutant APC allele. The data show that 36.6% of the mutation-positive family members have fewer than 10 colonic adenomatous polyps, and 3 (6.8%) of these individuals were diagnosed with colorectal cancer.

CONCLUSIONS

In view of the apparent age of this mutation, a notable fraction of both multiple-adenoma patients and perhaps even colon cancer cases in the United States could be related to this founder mutation. The colon cancer risk associated with the mutation makes genetic testing of considerable importance in patients with a personal or family history of either colonic polyps or cancer at a young age.

Variable Phenotypic Expression of Identical MYH Germline Mutations in Siblings with Attenuated Familial Adenomatous Polyposis

Germline mutations in the Mutant-Y-homologue (MYH) gene have been linked to an attenuated form of familial adenomatous polyposis in patients who express a wild-type adenomatous polyposis coli gene. However, the diverse clinical manifestations of MYH mutations have not been fully elucidated. We report a case of siblings with identical germline mutations in the MYH gene, one of whom developed a locally advanced colon adenocarcinoma with few other adenomatous lesions, whereas the other had numerous benign colonic polyps. The variable genotype–phenotype manifestations of MYH mutations and the attenuated familial adenomatous polyposis syndrome are discussed.

Colorectal adenomatous polyposis Associated with MYH mutations: genotype and phenotype characteristics

PURPOSE

Recent literature reports that several digestive diseases are associated with mutations in the base excision repair gene MYH. This study was designed to establish the prevalence of germ-line MYH mutations in a series of 56 consecutive patients with no detectable APC mutation and describe the phenotype of those with MYH mutations.

METHODS

MYH mutations were screened by DNA sequencing after polymerase chain reaction amplification of each exon. Clinical, endoscopic, and surgical data were collected for the tested patients.

RESULTS

MYH mutations were identified only in the group of patients with attenuated adenomatous polyposis with ten or more adenomatous polyps. The prevalence of MYH mutations was 34.4 percent (11 cases) in this subgroup of 30 patients. There were two homozygotes and eight compound heterozygotes. Only one patient had a monoallelic mutation. At least one of two mutational hot spots was identified in ten patients. Three patients presented with a family history of adenomatous polyposis in siblings, without vertical transmission. The median number of colorectal adenomatous polyps was 53 without preferential localization. Colorectal cancer was associated with polyposis in seven patients. Gastric and duodenal adenomas were diagnosed in one case. Ten of 11 patients underwent colectomy.

CONCLUSIONS

MYH mutations have been observed in one-third of patients with attenuated polyposis. The phenotype of the disease is similar to attenuated familial adenomatous polyposis. Upper gastrointestinal endoscopy also should be recommended. However, its transmission shows evidence of a recessive pattern.

Immunohistochemical staining for mismatch repair proteins, and its relevance in the diagnosis of hereditary non-polyposis colorectal cancer

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) arises mostly from germline mutations of the mismatch repair genes MSH2 and MLH1. The diagnosis of HNPCC is based on a set of clinical criteria that may be too restrictive to identify all affected patients. Immunohistochemical staining (IHC) for the mismatch repair proteins, MutS homologue 2 (MSH2) and MutL homologue 1 (MLH1), reliably identifies the microsatellite instability phenotype. This study evaluated the ability of IHC to detect germline mutations in an unselected group of patients with colorectal cancer (CRC).

METHODS

All patients with CRC operated on between July 2000 and March 2003, and demonstrating a loss of protein, were contacted. Following informed consent, searchs for germline mutation and methylation of the promoter were performed on normal and tumoral DNA.

RESULTS

Thirty patients agreed to participate, four of whom fulfilled the Amsterdam II criteria. Loss of expression of MLH1 was found in 20 patients, and loss of expression of MSH2 in ten patients. Four of the MLH1-deficient patients had a germline MLH1 point mutation (positive predictive value (PPV) 20 (95 per cent confidence interval (c.i.) 2 to 38 per cent) and 11 had promoter methylation. Seven of the MSH2-deficient patients had a germline MSH2 point mutation (PPV 70 (95 per cent c.i. 54 to 96 per cent), and none showed promoter methylation.

CONCLUSION

MLH1-deficient patients who are young or have a positive family history of cancer should be referred for genetic testing and counselling, whereas MSH2-deficient patients should be counselled in the same way as patients with HNPCC.

Very high incidence of familial colorectal cancer in Newfoundland: a comparison with Ontario and 13 other population-based studies

Newfoundland has the highest rate of colorectal cancer (CRC) of any Canadian province. In order to investigate the factors, especially genetic components, responsible for CRC we established the Newfoundland Colorectal Cancer Registry. In a 5-year period we examined every case of CRC diagnosed under the age of 75 years and obtained consent from 730 cases. Careful analysis of family history was used to assign a familial cancer risk, based on established criteria. We observed that 3.7% of CRC cases came from families meeting the Amsterdam II criteria and a further 0.9% of cases involved familial adenomatous polyposis (FAP). An additional 43% of cases met one or more of the revised Bethesda criteria and 31% of all cases had a first-degree relative affected with CRC. We compared the Newfoundland data with data from the province of Ontario, where the same recruitment and risk-assessment criteria were used. In all categories, the indicators of familial risk were significantly higher in Newfoundland. These data were also compared to results published from 13 other population-based studies worldwide. In every category the proportion of Newfoundland cases meeting the criteria was higher than in any other population. The mean differences were: 3.5-fold greater for FAP, 2.8-fold higher for Amsterdam criteria, 2.0-fold higher for Bethesda criteria and 1.9-fold higher for the number of affected first-degree relatives. We conclude that the high incidence of CRC in Newfoundland may be attributable to genetic, or at least familial, factors. In the high-risk families we provide evidence for the involvement of founder mutations in the APC and MSH2 genes.

Polipose adenomatosa familiar atenuada

A Polipose Adenomatosa Familiar Atenuada(PAFA) é uma síndrome autossômica dominante, de diagnóstico tardio, comparando-se à forma clássica da polipose adenomatosa familiar. Dentre as características da síndrome estão: a)presença de menos de 100 pólipos colorretais; b) curso brando da doença, com idade tardia do diagnóstico e do aparecimento de câncer; c)prevalência maior dos pólipos à direita do cólon; d) reto poupado de lesões, na maioria dos casos. Analisar as características clínicas, tratamento e seguimento de 13 pacientes com diagnóstico de PAFA. Dos pacientes estudados, a média de idade ao diagnóstico foi 55 anos. Cinco pacientes apresentavam história familiar de polipose e/ou neoplasia. Nove (69%) pacientes já tinham câncer no momento do diagnóstico. A maioria dos pacientes possuía pólipos localizados no cólon direito (31%). Do total, 06 pacientes foram submetidos à ressecção cirúrgica, com proctocolectomia ou colectomia. A média de seguimento dos pacientes foi de 26 meses. O controle foi realizado através de colonoscopias e retossigmoidoscopias, de acordo com o tratamento realizado. O diagnóstico de PAFA foi feito em idade tardia em relação à forma clássica da doença, com a maioria dos pólipos localizados no cólon direito. O controle endoscópico dos pacientes deve ser realizado com rigor. A colectomia com anastomose do íleo-reto é uma boa opção cirúrgica no tratamento dos pacientes, com baixa recidiva de pólipos no reto.

Investigation of pathogenic mechanisms in multiple colorectal adenoma patients without germline APC or MYH/MUTYH mutations

Patients with multiple (5–100) colorectal adenomas (MCRAs) often have no germline mutation in known predisposition genes, but probably have a genetic origin. We collected a set of 25 MCRA patients with no detectable germline mutation in APC, MYH/MUTYH or the mismatch repair genes. Extracolonic tumours were absent in these cases. No vertical transmission of the MCRA phenotype was found. Based on the precedent of MYH-associated polyposis (MAP), we searched for a mutational signature in 241 adenomatous polyps from our MCRA cases. Somatic mutation frequencies and spectra at APC, K-ras and BRAF were, however, similar to those in sporadic colorectal adenomas. Our data suggest that the genetic pathway of tumorigenesis in the MCRA patients' tumours is very similar to the classical pathway in sporadic adenomas. In sharp contrast to MAP tumours, we did not find evidence of a specific mutational signature in any individual patient or in the overall set of MCRA cases. These results suggest that hypermutation of APC does not cause our patients' disease and strongly suggests that MAP is not a paradigm for the remaining MCRA patients. Our MCRA patients' colons showed no evidence of microadenomas, unlike in MAP and familial adenomatous polyposis (FAP). However, nuclear β-catenin expression was significantly greater in MCRA patients' tumours than in sporadic adenomas. We suggest that, at least in some cases, the MCRA phenotype results from germline variation that acts subsequent to tumour initiation, perhaps by causing more rapid or more likely progression from microadenoma to macroadenoma.

[Colorectal carcinogenesis. 1. Hereditary predisposition and colorectal cancer]

Tumors arising sporadically represent 70-80% of colorectal cancer (CRC). The two best defined forms of inherited CRC-familial multiple polyposis (FMP) and Hereditary Non-Polyposis Colon Cancer (HNPCC) account respectively for<1% and 2-3% of CRC. These rare genetic syndromes (FMP, HNPCC, Peutz-Jeghers Syndrome) are caused by major predisposing gene mutations (APC gene, MMR gene, BMPR1A. SMAD4,...) and local environmental factors play only a minor role. In the sporadic forms of CRC, 25% have significant genetic predisposition probably related to alleles with weak penetration (APC*I1307K, TGFbR1*6Ala...) and are more strongly affected by environmental factors.

Familial adenomatous polyposis complicated with an invasive colo-rectal adenocarcinoma in a 26-year-old Nigerian male ? a rare finding

Familial adenomatous polyposis is very rare in our environment. This condition occurring with a complication of a colorectal cancer has never been reported to the best of our knowledge. We present a case of a 26-year-old Nigerian man who came to us in February this year with a 10-year history of watery stool, which is also mucoid with tenesmus. There was also associated weight loss and colicky abdominal pains. He had also previously had a previous proctoscopy and rectal biopsy that showed numerous adenomatous polyps with dysplastic changes confirmed by histology. Barium enema revealed multiple polyps up to the right side of the transverse colon. Repeat histology after panproctocolectomy confirmed foci of invasive adenocarcinoma of the colon up to the muscle coat. The patient post-operatively is alive and well.

MYH, OGG1, MTH1, and APC alterations involved in the colorectal tumorigenesis of Korean patients with multiple adenomas

This study was done to characterize base excision repair (BER) genes and adenomatous polyposis coli (APC) alterations in the tumorigenesis of multiple colorectal adenomas in Korean patients. In total, 217 adenomas (mean number = 10) and 117 cancers were available from 143 patients. The heterozygous genotype of OGG1 c.1-18G>T was closely associated with multiple adenoma families (P < 0.001), while MYH A359V mutation exhibited a tendency (P = 0.053). MYH R170G mutation was exclusively identified in one patient. The G:C>T:A transversion or attenuated familial adenomatous polyposis (AFAP) mutations of APC was identified in the specific genotypes of BER variants. Tubular adenomas or adenomas with none-to-mild dysplasia were significantly associated with polymorphic genotypes of OGG1 IVS4-15 and S326C. In addition, large and pedunculated adenomas were more frequent in patients with G:C>T:A transversion and AFAP mutations of APC, respectively. However, BER variants were not associated with mismatch repair or altered p53 protein expression. Conclusively, two novel mutations of MYH and a novel OGG1 polymorphism seemed to be associated with multiple colorectal adenomas in Korean families, differing from those in other ethnic groups. Some BER variants involved in specific APC mutations are associated with characteristics of histogenesis other than altered mismatch repair or p53 pathway.

Implication of MYH in colorectal polyposis

OBJECTIVE

The aim of this study was to determine the frequency of MYH mutations in one large population of polyposis patients without APC mutation identified.

SUMMARY BACKGROUND DATA

Familial adenomatous polyposis (FAP) is the most known inherited colorectal cancer syndrome. In 70% to 80% of polyposis patients, an APC mutation is found. Patients with polyposis but no APC mutation are considered as APC-muted patients and followed as their relatives accordingly. Biallelic mutation of MYH has been found to responsible of colorectal polyposis and cancer in an autosomal recessive pattern of inheritance.

METHODS

Between 1978 and 2004, 433 patients were operated for polyposis. A mutation on APC was identified in 322 patients. Among the remaining patients, 44 were identified as possible MYH-muted patients and contacted, and 31 signed informed consent. Clinical data were obtained from the patients' medical notes. Germline mutation of MYH was searched by sequencing the whole gene. To confirm the deleterious effects of biallelic MYH mutation, transversions on K-ras and APC were searched.

RESULTS

There were 9 women and 22 men with a mean age of 53.9 years (range, 22-68 years) at the time of diagnosis. The mean number of polyps was 62.8 (range, 11-266). Eighteen patients (58.1%) had a colorectal cancer. We found biallelic MYH mutation in 6 patients (19.3%; 95% confidence interval, 5.2%-33.5%) and 5 (83.3%) had transversions in K-ras and/or APC.

CONCLUSION

MYH is a new gene responsible for about 1.4% of all adenomatous polyposis and about 20% of adenomatous polyposis without APC mutation identified. Search for MYH biallelic mutation in these patients should be systematic as it changes their and relatives'surveillance.

The genetics of FAP and FAP-like syndromes

The presence of multiple adenomatous polyps in the large bowel confers a high lifetime risk of colorectal cancer. Although many cases of classical familial adenomatous polyposis (> 100 polyps) can be accounted for by mutations in the adenomatous polyposis coli (APC) gene, a large group of patients remains with multiple (5-100) adenomas and in whom there is no detectable APC mutation. Recently two new genetic variants have been found to be associated with multiple colorectal adenomas and cancer, MYH/MUTYH on chromosome 1p and the HMPS/CRAC1 locus on chromosome 15q13-q14. New information also continues to emerge regarding the less common hamartomatous polyposis conditions, Peutz-Jeghers syndrome and Juvenile Polyposis syndrome. In approximately half to two thirds of these families, germline genetic variants can now be uncovered. In this review we draw together some of the most recent information pertinent to the molecular pathogenesis of colorectal polyposis.

APC E1317Q Is Not Associated with Colorectal Cancer in a Population-Based Case-Control Study in Northern Israel

A variant in the adenomatous polyposis coli gene, APC E1317Q, has been inconsistently associated with risk of colorectal cancer. We used data collected as a part of the Molecular Epidemiology of Colorectal Cancer study, a population-based study of colorectal cancer in northern Israel (1,834 matched cases and controls), to evaluate the relationship between this variant and risk of sporadic colorectal cancer. There was no association between E1317Q and colorectal cancer [odds ratio (OR), 1.15; 95% CI, 0.65-2.02]. When the control sample was restricted to polyp-free controls, the OR was 0.87 (95% CI, 0.36-2.14), indicating that this result is unlikely to be due to nondifferential misclassification due to undiagnosed polyps. A meta-analysis including these data and prior published reports found a nonsignificant summary OR nearly identical to the association reported here in the Molecular Epidemiology of Colorectal Cancer case-control study. Although there are previously published reports addressing this question, due to the low frequency of the variant, many of these studies lack the power to estimate the risk in a meaningful way. Given the substantial size of our study and the consistency of our findings with the results of our meta-analyses, we conclude that it is unlikely that APC E1317Q is associated with a clinically meaningful risk of colorectal cancer.

Cancer genetics: colorectal cancer as a model

Cancer is essentially a somatic evolutionary process and is, therefore, effectively defined by the genetic and epigenetic changes underlying this process. An understanding of the function of these changes is fundamental to devising new approaches to prevention and treatment. Colorectal cancer (CRC), apart from its obvious importance as one of the most frequent cancers, provides an excellent model for such studies because of the availability of precursor adenoma lesions and the existence of several clear-cut familial inherited susceptibilities. These include familial adenomatous polyposis (FAP), which led to the identification of the APC gene and the importance of the Wnt pathway, and hereditary non-polyposis CRC (HNPCC), which identified the role of the mismatch repair genes in colorectal and other cancers. The presently known range of genetic and epigenetic changes in CRCs and adenomas is reviewed in this paper and the evidence against a requirement for genomic instability presented, together with a discussion of patterns of gene methylation, including especially our work on the homeobox gene, CDX1. Clearly, familial cancers, such as FAP and HNPCC, cannot account for more than perhaps 5% of the incidence of CRC. There is, however, evidence that approximately a further 25-30% have some inherited susceptibility. Based on the association of APC missense variants with multiple adenomas, we proposed that much of this may be due to the cumulative effects of low frequency, low penetrance variants, and the "rare variant hypothesis". The evidence for this from our work on multiple adenoma cases, and certain other examples, is discussed.

Single nucleotide polymorphisms of the APC gene and colorectal cancer risk: a case-control study in Taiwan

Background

Colorectal cancer (CRC), which has become especially prevalent in developed countries, is currently the third highest cause of cancer mortality in Taiwan. Mutation of the adenomatous polyposis coli (APC) gene, a tumour suppressor, is thought to be an early event in colorectal tumourigenesis. To date, however, no large-scale screening for APC gene variants in Chinese subjects has been performed. The present study was undertaken to identify APC gene variants that are significantly associated with the occurrence of CRC in Taiwanese subjects.

Methods

In order to compare the genotype distribution of variant sites, the full-length APC genes of 74 healthy individuals and 80 CRC patients were sequenced.

Results

Among the 154 Taiwanese subjects examined in this study, three new mutations, but no previously reported mutations, were found. One deletion at codon 460 leading to a frameshift and two missense mutations resulting in p.V1125A and p.S1126R substitutions were identified. Additionally, three high risk genotypes associated with three single nucleotide polymorphisms and one low risk genotype at codon 1822 were identified.

Conclusion

The findings of this case-control study are consistent with the proposal that Taiwanese subjects differ from other subjects with respect to phenotypic presentation of APC and CRC risk.

Absence of MutY homologue mutation in patients with multiple sporadic adenomatous polyps in Korea

AIM: Recently, germ-line mutation in the base excision repair gene MYH has been identified to cause a novel autosomal recessive form of familial adenomatous polyposis (FAP). Interestingly, a striking evidence for MYH mutations within different ethnic groups has been demonstrated. In this study, we screened 30 patients with multiple adenomatous polyps for MYH mutations to assess its prevalence and ethnic specificity in Korea.

METHODS: Thirty patients (21 men and 9 women; mean age 62.3 years) with multiple adenomatous polyps were examined for MYH mutations. The mean number of adenomas per patient was 10.0. Sixteen exonic regions and their intronic sequences were amplified by PCR and subjected to SSCP and DNA sequencing analyses.

RESULTS: None of the patients was identified to carry any truncating or sequence alterations in MYH. Our screening for the mutational regions, which were recognized from Caucasian patients or affected Indian families, also failed to detect sequence substitutions.

CONCLUSION: Mutation in MYH may be rarely involved in the pathogenesis of multiple sporadic colorectal adenomas in Korean population, although a large-scale analysis will be required to clarify the presence of specific MYH variants in a subset of patients and their role in the predisposition of multiple colorectal adenomas in Korean population.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal-dominant colorectal cancer syndrome, caused by a germline mutation in the adenomatous polyposis coli (APC) gene, on chromosome 5q21. It is characterized by hundreds of adenomatous colorectal polyps, with an almost inevitable progression to colorectal cancer at an average age of 35 to 40 yr. Associated features include upper gastrointestinal tract polyps, congenital hypertrophy of the retinal pigment epithelium, desmoid tumors, and other extracolonic malignancies. Gardner syndrome is more of a historical subdivision of FAP, characterized by osteomas, dental anomalies, epidermal cysts, and soft tissue tumors. Other specified variants include Turcot syndrome (associated with central nervous system malignancies) and hereditary desmoid disease. Several genotype-phenotype correlations have been observed. Attenuated FAP is a phenotypically distinct entity, presenting with fewer than 100 adenomas. Multiple colorectal adenomas can also be caused by mutations in the human MutY homologue (MYH) gene, in an autosomal recessive condition referred to as MYH associated polyposis (MAP). Endoscopic screening of FAP probands and relatives is advocated as early as the ages of 10-12 yr, with the objective of reducing the occurrence of colorectal cancer. Colectomy remains the optimal prophylactic treatment, while the choice of procedure (subtotal vs proctocolectomy) is still controversial. Along with identifying better chemopreventive agents, optimizing screening of extracolonic cancers and applying new radiological and endoscopic technology to the diagnosis and management of extracolonic features are the major challenges for the future.

Twelve years of endoscopic surveillance in a family carrying biallelic Y165C MYH defect: report of a case

PURPOSE

We report the case of two siblings, clinically andendoscopically followed for 12 years, who displayed anattenuated adenomatous polyposis coli phenotype.

METHODS

On workup for rectal bleeding with colonoscopy, we found multiple adenomas mainly right-sided in a 21-year-old female and the same colonic phenotype was observed in her 27-year-old brother. We made a clinical diagnosis of attenuated adenomatous polyposis coli and performed APC gene testing. Because they had refused the proposed ileorectal anastomosis surgical option, we planned a periodic, endoscopic follow-up.

RESULTS

Gene testing did not confirm the clinical suspicion of attenuated adenomatous polyposis coli. Actually, we did not find anypathogenic mutation in APC gene and we recently identified a biallelic Y125C MYH defect. During the endoscopic follow-up, a progressive reduction of adenomas was seen.

CONCLUSIONS

New insight colorectal cancer genetics have allowed definition of a new class of polyposis that applies to some patients with attenuated adenomatous polyposis coli phenotype as in the siblings we have described. To prevent colorectal cancer without recurring to surgery, colonoscopic polypectomy may be a suitable tool in controlling MYH polyposis.

The dialectics of cancer: A theory of the initiation and development of cancer through errors in RNAi

The recent discoveries of the RNA-mediated interference system in cells could explain all of the known features of human carcinogenesis. A key, novel idea, proposed here, is that the cell has the ability to recognise a mutated protein and/or mRNA. Secondly, the cell can generate its own short interfering RNA (siRNA) using an RNA polymerase to destroy mutated mRNA, even when only a single base pair in the gene has mutated. The anti-sense strand of the short RNA molecule (called sicRNA), targets the mutated mRNA of an oncogene or a tumour suppressor. The resulting double stranded RNA, using the RNA-induced silencing complex in the cytoplasm dices the mutated mRNA. In cancer-prone tissues, during cell mitosis, the sicRNA complex can move into the nucleus to target the mutated gene. The sicRNA, possibly edited by dsRNA-specific adenosine deaminase, converting adenosines to inosines, can be retained in the nucleus, with enhanced destructive capability. The sicRNA triggers the assembly of protein complexes leading to epigenetic modification of the promoter site of the mutant gene, specifically methylation of cytosines. In some instances, instead of methylation, the homologous DNA is degraded, leading to loss of heterozygosity. The factors controlling these two actions are unknown but the result is gene silencing or physical destruction of the mutant gene. The cell survives dependent on the functioning of the single, wild-type allele. An error in RNAi defence occurs when the sicRNA enters the nucleus and targets the sense strand of the wrong DNA. The sicRNA, because of the similarity of its short sequence and relaxed stringency, can target other RNAs, which are being transcribed. This can result in the methylation of the wrong promoter site of a gene or LOH of that region. In the vast majority of these cases, the aberrant hybridisations will have no effect on cell function or apoptosis eliminates non-viable cells. On a rare occasion, a preneoplastic cell is initiated when aberrant hybridisations switches on/off a gene involved in apoptosis, as well as a gene involved in cell proliferation and DNA damage surveillance. Genetic instability results when the sicRNA competes for a repeat sequence in the centromere or telomere, leading to gross chromosomal rearrangements. A malignancy develops when the sicRNAs fortuitously targets a microRNA (miRNA) or activates a transcription factor, resulting in the translation of a large number of new genes, alien to that tissue. This leads to dedifferentiation of the tissue, a resculpting of the histone code, chromosomal rearrangements, along a number of specific pathways, the gain of immortality and the dissemination of a metastatic cancer.

Colorectal polyps in carriers of the APC I1307K polymorphism

PURPOSE

The probability of colorectal cancer is moderately increased among carriers of the APC I1307K polymorphism. However, it is not known if endoscopic surveillance of this high-risk group is warranted. The prevalence of polyps and adenomas in specimens of colorectal cancer who are carriers and noncarriers of the APC I1307K polymorphism is compared.

METHOD

Prevalence of adenomatous polyps in the pathology specimens of the study participants, stratified by their APC I1307K polymorphism status, was studied in 900 consecutive cases of colorectal cancer diagnosed in northern Israel between 1998 and 2002, within the framework of a population-based, case-controlled study (MECC Study).

RESULTS

The APC I1307K mutation was detected in 78 colorectal cancer cases (8.7 percent) of the study population. Prevalence was higher among Ashkenazi Jews (11.2 percent) than among non-Ashkenazi Jews (2.7 percent) or Arabs (3.1 percent). After adjustment for age, APC I1307K carriers were significantly more likely than noncarriers to have polyps in their surgical specimen (51.3 percent vs. 32.6 percent, P = 0.002). Adenomas with a tubular component (either tubular adenomas or tubulovillous adenomas), but not villous adenomas, were significantly more frequent among carriers (37.2 percent vs. 23.6 percent, P = 0.005).

CONCLUSION

Together with former evidence of I1307K being a risk factor for colorectal cancer, these data suggest that colonoscopic surveillance for colorectal adenomas and cancer may be warranted in I1307K carriers, even in the absence of other identifiable risk factors.

Prophylaktische Chirurgie der familiären adenomatösen Polyposis coli

Familial adenomatous polyposis coli (FAP) may not be considered a single disease entity with standardized guidelines for operative treatment. However, prophylactic colectomy after the manifestation of polyps but prior to the development of colorectal cancer is essential. The optimal timing of prophylactic surgery remains a clinical decision taken independently of mutation analysis. In case of the classic FAP phenotype, restorative proctocolectomy and ileal pouch-anal anastomosis is the procedure of choice. The development of reliable guidelines for attenuated FAP variants requires further evidence from clinical studies on surgical strategy and the advantages of prophylactic surgery over regular endoscopic screening with removal of polyps.