Attenuated familial adenomatous polyposis due to a mutation in the 3' part of the APC gene. A clue for understanding the function of the APC protein

Attenuated Familial Adenomatous Polyposis: A Phenotypic Diagnosis but Obsolete Term?

BACKGROUND

Attenuated familial adenomatous polyposis is characterised by low number (≤100) and delayed development of colorectal adenomas. Various definitions have been used, and genotype-phenotype correlations have been suggested.

OBJECTIVE

We aimed to evaluate phenotypic and genotypic correlation in patients with presumed attenuated familial adenomatous polyposis and assess familial variability.

DESIGN

This is a retrospective study.

SETTINGS

This study was conducted at a tertiary polyposis registry.

PATIENTS

Individuals with attenuated familial adenomatous polyposis were identified. Phenotypic group was defined as 100 or fewer adenomas at age 25 years and genotypic group was defined as a variant in the adenomatous polyposis coli region associated with attenuated familial adenomatous polyposis. Pathology polyp count was used for patients who had undergone surgery and endoscopic polyp count for those with intact colon.

MAIN OUTCOME MEASURES

We evaluated phenotypic and genotypic correlation in patients with presumed attenuated familial adenomatous polyposis and familial variability.

RESULTS

A total of 69 patients were identified in the phenotypic group, of whom 54 (78%) had a pathogenic variant in the attenuated regions of the adenomatous polyposis coli gene. Forty-eight (70%) had intact colon (median age at last colonoscopy 43 [25-73] years; median endoscopic polyp count 20 [0-100]) and 21 (30%) had undergone colectomy (median age at surgery 45 [25-54] years; median pathology polyp count 43 [3-100]). Eighty-three patients were identified in the genotypic group of which 54 (65%) had attenuated phenotype. Inter- and intrafamilial variability were observed.

LIMITATIONS

This study was limited by its retrospective nature and single-center experience.

CONCLUSION

Phenotype in familial adenomatous polyposis lies on a spectrum and is determined in part by genotype and age at adenoma count. Diagnosis of attenuated familial adenomatous polyposis should be based on phenotype; genotype is not a reliable indicator. Management should be personalized according to the phenotype of each individual. See Video Abstract at http://links.lww.com/DCR/B775.

POLIPOSIS ADENOMATOSA FAMILIAR ATENUADA UN DIAGNSTICO FENOTPICO PERO TRMINO OBSOLETO

ANTECEDENTES:La poliposis adenomatosa familiar atenuada se caracteriza por un número bajo (≤100) y desarrollo retardado de adenomas colorrectales. Se han utilizado varias definiciones y se han sugerido correlaciones genotipo-fenotipo.OBJETIVO:Nuestro objetivo es evaluar la correlación fenotípica y genotípica en pacientes con presunta poliposis adenomatosa familiar atenuada y evaluar la variabilidad familiar.DISEÑO:Este es un estudio retrospectivo.AJUSTE:Este estudio se realizó en un registro terciario de poliposis.PACIENTES:Se identificaron individuos con poliposis adenomatosa familiar atenuada. El grupo fenotípico se definió como ≤100 adenomas a la edad de 25 años y el grupo genotípico se definió como una variante en la región de poliposis coli adenomatosa asociada con poliposis adenomatosa familiar atenuada. Se utilizó el recuento de pólipos en patología para los pacientes que se habían sometido a cirugía y el recuento de pólipos endoscópico para los que tenían el colon intacto.PRINCIPALES MEDIDAS DE RESULTADO:Evaluamos la correlación fenotípica y genotípica en pacientes con presunta poliposis adenomatosa familiar atenuada y variabilidad familiar.RESULTADOS:Un total de 69 pacientes se identificaron en el grupo fenotípico de los cuales 54 (78%) tenían una variante patogénica en las regiones atenuadas del gen de la poliposis coli adenomatosa. Cuarenta y ocho (70%) tenían colon intacto (edad media en la última colonoscopia 43 [25-73] años; mediana del recuento de pólipos endoscópicos 20 [0-100]) y 21 (30%) se habían sometido a colectomía (edad edia en el momento de la cirugía 45 [25-54] años; mediana del recuento de pólipos patológicos 43 [3-100]). Se identificaron 83 pacientes en el grupo genotípico de los cuales 54 (65%) tenían fenotipo atenuado. Se observó variabilidad inter e intrafamiliar.LIMITACIONES:Este estudio estuvo limitado por su naturaleza retrospectiva y la experiencia de un solo centro.CONCLUSIÓNES:El fenotipo en la poliposis adenomatosa familiar se encuentra en un espectro, determinado en parte por el genotipo y la edad en el momento del recuento de adenomas. El diagnóstico de poliposis adenomatosa familiar atenuada debe basarse en el fenotipo; el genotipo no es un indicador confiable. El manejo debe personalizarse según el fenotipo de cada individuo. Consulte Video Resumen en http://links.lww.com/DCR/B775.

Importance of sessile serrated lesions in a patient with familial adenomatous polyposis

A 28-year-old male visited hospital because his mother had been diagnosed with familial adenomatous polyposis (FAP) with a pathological variant of the APC gene. Total colonoscopy showed that he has more than 100 polyps distributed throughout the colorectum, and the APC gene variant was also detected. After he was diagnosed with FAP, he received information that surgery was currently the only way to prevent the development of colorectal cancer. However, he firmly declined to undergo surgical procedures and decided to have strict follow-up with frequent endoscopic polypectomy to prevent the development of colorectal cancer. At the first endoscopy, polypectomy was performed on 52 polyps. Histological analysis of the dissected polyps showed that they were all adenomas, but adenocarcinoma was not detected. The second endoscopic polypectomy was performed after 4 months later. We found a pale 20 mm wide flat, elevated type polyp in the ascending colon with an adherent mucus cap that was resistant to washing off. After endoscopic mucosal resection, histological analysis revealed that there were two lesions in the polyps, a sessile serrated lesion (SSL) and SSL with dysplasia. SSL is a high-risk lesion for colorectal cancer, but it was reported to be rare in patients with FAP, and the existence of SSL suggested another carcinogenesis pathway in patients with FAP in addition to the adenoma-carcinoma sequence. Our report may be significant not only in consideration of the pathogenesis of FAP but also useful to raise awareness of SSL for clinicians who perform endoscopic polypectomy to prevent the development of colorectal cancer in patients with FAP.

Different Expressivity of two Adjacent Mutations of the APC Gene

Aims and background

The phenotypic expression of different APC mutations in familial adenomatous polyposis (FAP) is variable: two to three variants of the disease have been defined based on the severity of colonic manifestations. Age of onset and number of polypectomies per person-year of postsurgical follow-up were compared in two FAP families with very close mutation sites in the APC gene, in order to ascertain mutation-specific variation of expressivity.

Families and APC mutations

Family A (5 patients) carried a newly characterized mutation, a four bp deletion at codon 843. Family B (5 patients) carried a previously identified mutation at codon 835.

Results

Mean age of onset was 49.7 years in family A and 30.5 years in family B; number of polypectomies per person-year of follow-up was 1.05 for family A and 10.1 for family B (P <0.001).

Conclusions

There is significant variation of expressivity (allelic heterogeneity) in FAP between two mutations separated by only eight codons, located at the 5’ extremity of APC gene exon 15.

Contribution of APC and MUTYH mutations to familial adenomatous polyposis susceptibility in Hungary

Familial adenomatous polyposis (FAP) is a colorectal cancer predisposition syndrome with considerable genetic and phenotypic heterogeneity, defined by the development of multiple adenomas throughout the colorectum. FAP is caused either by monoallelic mutations in the adenomatous polyposis coli gene APC, or by biallelic germline mutations of MUTYH, this latter usually presenting with milder phenotype. The aim of the present study was to characterize the genotype and phenotype of Hungarian FAP patients. Mutation screening of 87 unrelated probands from FAP families (21 of them presented as the attenuated variant of the disease, showing <100 polyps) was performed using DNA sequencing and multiplex ligation-dependent probe amplification. Twenty-four different pathogenic mutations in APC were identified in 65 patients (75 %), including nine cases (37.5 %) with large genomic alterations. Twelve of the point mutations were novel. In addition, APC-negative samples were also tested for MUTYH mutations and we were able to identify biallelic pathogenic mutations in 23 % of these cases (5/22). Correlations between the localization of APC mutations and the clinical manifestations of the disease were observed, cases with a mutation in the codon 1200-1400 region showing earlier age of disease onset (p < 0.003). There were only a few, but definitive dissimilarities between APC- and MUTYH-associated FAP in our cohort: the age at onset of polyposis was significantly delayed for biallelic MUTYH mutation carriers as compared to patients with an APC mutation. Our data represent the first comprehensive study delineating the mutation spectra of both APC and MUTYH in Hungarian FAP families, and underscore the overlap between the clinical characteristics of APC- and MUTYH-associated phenotypes, necessitating a more appropriate clinical characterization of FAP families.

Hereditary cancer syndromes as model systems for chemopreventive agent development

Research in chemoprevention has undergone a shift in emphasis for pragmatic reasons from large, phase III randomized studies to earlier phase studies focused on safety, mechanisms, and utilization of surrogate endpoints such as biomarkers instead of cancer incidence. This transition permits trials to be conducted in smaller populations and at substantially reduced costs while still yielding valuable information. This article will summarize some of the current chemoprevention challenges and the justification for the use of animal models to facilitate identification and testing of chemopreventive agents as illustrated though four inherited cancer syndromes. Preclinical models of inherited cancer syndromes serve as prototypical systems in which chemopreventive agents can be developed for ultimate application to both the sporadic and inherited cancer settings.

Wnt/β-catenin signaling plays an ever-expanding role in stem cell self-renewal, tumorigenesis and cancer chemoresistance

Wnt signaling transduces evolutionarily conserved pathways which play important roles in initiating and regulating a diverse range of cellular activities, including cell proliferation, calcium homeostasis, and cell polarity. The role of Wnt signaling in controlling cell proliferation and stem cell self-renewal is primarily carried out through the canonical pathway, which is the best-characterized the multiple Wnt signaling branches. The past 10 years has seen a rapid expansion in our understanding of the complexity of this pathway, as many new components of Wnt signaling have been identified and linked to signaling regulation, stem cell functions, and adult tissue homeostasis. Additionally, a substantial body of evidence links Wnt signaling to tumorigenesis of cancer types and implicates it in the development of cancer drug resistance. Thus, a better understanding of the mechanisms by which dysregulation of Wnt signaling precedes the development and progression of human cancer may hasten the development of pathway inhibitors to augment current therapy. This review summarizes and synthesizes our current knowledge of the canonical Wnt pathway in development and disease. We begin with an overview of the components of the canonical Wnt signaling pathway and delve into the role this pathway has been shown to play in stemness, tumorigenesis, and cancer drug resistance. Ultimately, we hope to present an organized collection of evidence implicating Wnt signaling in tumorigenesis and chemoresistance to facilitate the pursuit of Wnt pathway modulators that may improve outcomes of cancers in which Wnt signaling contributes to aggressive disease and/or treatment resistance.

Genetic predisposition to colorectal cancer: Where we stand and future perspectives

The development of colorectal cancer (CRC) can be influenced by genetic factors in both familial cases and sporadic cases. Familial CRC has been associated with genetic changes in high-, moderate- and low-penetrance susceptibility genes. However, despite the availability of current gene-identification techniques, the genetic causes of a considerable proportion of hereditary cases remain unknown. Genome-wide association studies of CRC have identified a number of common low-penetrance alleles associated with a slightly increased or decreased risk of CRC. The accumulation of low-risk variants may partly explain the familial risk of CRC, and some of these variants may modify the risk of cancer in patients with mutations in high-penetrance genes. Understanding the predisposition to develop CRC will require investigators to address the following challenges: the identification of genes that cause uncharacterized hereditary cases of CRC such as familial CRC type X and serrated polyposis; the classification of variants of unknown significance in known CRC-predisposing genes; and the identification of additional cancer risk modifiers that can be used to perform risk assessments for individual mutation carriers. We performed a comprehensive review of the genetically characterized and uncharacterized hereditary CRC syndromes and of low- and moderate-penetrance loci and variants identified through genome-wide association studies and candidate-gene approaches. Current challenges and future perspectives in the field of CRC predisposition are also discussed.

The APC p.I1307K polymorphism is a significant risk factor for CRC in average risk Ashkenazi Jews

BACKGROUND

The p.I1307K adenomatous polyposis coli (APC) gene variant, prevalent among Ashkenazi Jews, may increase the risk for colorectal neoplasia. We studied the clinical importance of screening for this polymorphism in 3305 Israelis undergoing colonoscopy.

PATIENTS AND METHODS

Clinical data regarding potential risk factors for colorectal cancer (CRC) were collected from individuals undergoing colonoscopic examination at the Tel-Aviv medical center. The APC p.I1307K was detected using real-time PCR (polymerase chain reaction) from DNA extracted from peripheral mononuclear cells.

RESULTS

The overall prevalence of the p.I1307K polymorphism was 8.0% (10.1% among Ashkenazi and 2.7% among Sephardic Jews, p<0.001). The overall adjusted odds ratio (OR) for colorectal neoplasia among carriers was 1.51 (95% confidence intervals (CI), 1.16-1.98). Among average risk Ashkenazi Jews, the adjusted OR was 1.75 (95% CI 1.26-2.45). A multiplicative interaction was identified between Ashkenazi ethnicity and APC p.I1307K carrier status (P(INTERACTION) = 0.055). The histopathological features of adenomas and carcinomas did not differ between carriers and non-carriers.

CONCLUSIONS

The APC p.I1307K gene variant is an important risk factor for colorectal neoplasia in average risk Ashkenazi Jews. Carriers in this group should be considered for screening colonoscopy at the age of 40, to be repeated every 5 years, similar to recommendations in individuals with family history of colorectal cancer.

Wnt signalling pathway in the serrated neoplastic pathway of the colorectum: possible roles and epigenetic regulatory mechanisms

The role of Wnt signalling in the serrated neoplastic pathway of colorectal tumourigenesis appears to be heterogeneous. Wnt pathway abnormalities contribute to the progression of at least a subset of traditional serrated adenomas of the colorectum, but may play a less active role in its pathogenesis compared with that in conventional adenoma-carcinoma. However, immunohistochemical studies of β-catenin in sessile serrated adenomas have shown wide variability, producing conflicting results on Wnt signalling activation in sessile serrated adenomas. DNA methylation, involving APC, SFRPs and mutated in colorectal cancer (MCC), may bridge the mutational gap of APC or β-catenin for activating Wnt signalling in serrated adenomas of the colorectum.

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.

Does intra-abdominal desmoid disease affect patients with an ileal pouch differently than those with an ileorectal anastomosis?

BACKGROUND

Nobody has analyzed the sequelae of desmoids according to the type of surgery that precipitated them.

OBJECTIVE

This study aims to determine whether the clinical effects of abdominal desmoids would be worse in patients with restorative proctocolectomy than in patients with ileorectal anastomosis.

DESIGN

This is a retrospective, database study.

PATIENTS

Included were patients with familial adenomatous polyposis who had undergone proctocolectomy with IPAA or colectomy and ileorectal anastomosis, and subsequently developed an intra-abdominal desmoid tumor.

MAIN OUTCOME MEASURES

The primary outcome measures were the clinical course of the desmoids; morbidity, and the requirement for stoma.

RESULTS

There were 86 patients: 49 had restorative proctocolectomy and 37 had ileorectal anastomosis. Patient demographics were similar. Average follow-up was 9.8 years (range, 2.7-23.8) and 16.3 years (range, 2.3 - 42.9). Treatment of the desmoids included surgery (64.4% vs 65.6%), medical therapy (69.4% vs 59.5%), chemotherapy (36.2% vs 30.0%), and radiotherapy (4.5% vs 10.0%), and was the same for each group. The overall complication rate of desmoids was similar, approaching 70%. The risk of individual complications was also similar (bleeding (2.0% vs 0.0%), fistula (10.2% vs 13.5%), bowel obstruction (32.7% vs 48.6%), pain (34.7% vs 21.6%), and death related to desmoid tumors (2.0% vs 10.8%)); 38.8% of the restorative proctocolectomy group and 51.4% the ileorectal group had surgery for desmoid tumor complications (P = .21), and 22.4% and 22.2% of patients ultimately had permanent stomas.

LIMITATIONS

This study was limited by the relatively small numbers of patients.

CONCLUSION

The morbidity associated with desmoid tumors has not been shown to differ, whether they arise after restorative proctocolectomy or ileorectal anastomosis.

FAP, gastric cancer, and genetic counseling featuring children and young adults: a family study and review

Familial adenomatous polyposis is a highly complex and multifaceted colorectal cancer prone disorder which is often significantly confounded by extracolonic cancers inclusive of gastric cancer, a significant problem in the Orient. Gastric cancer in familial adenomatous polyposis is heavily influenced by fundic gland polyps which are often so voluminous as to defy effective endoscopic surveillance. This study involves more than two decades of investigation of an attenuated familial adenomatous polyposis family where gastric cancer posed an early diagnostic problem because it was obscured by multiple fundic gland polyps. Fundic gland polyps are common in familial adenomatous polyposis and attenuated familial adenomatous polyposis and, if voluminous, may interfere with effective endoscopic gastric cancer surveillance. This family is believed to be the first of its type reported with focus upon education and genetic counseling in the setting of a family information service. Cancer control in familial adenomatous polyposis may be partially resolved through use of familial colorectal cancer registries, with greater attention to family history and its interpretation, genetic counseling, and clinical translation for diagnosis and management.

Mutational spectrum of APC and genotype-phenotype correlations in Greek FAP patients

BACKGROUND

Familial adenomatous polyposis, an autosomal dominant inherited disease caused by germline mutations within the APC gene, is characterized by early onset colorectal cancer as a consequence of the intrinsic phenotypic feature of multiple colorectal adenomatic polyps. The genetic investigation of Greek adenomatous polyposis families was performed in respects to APC and MUTYH germline mutations. Additionally, all available published mutations were considered in order to define the APC mutation spectrum in Greece.

METHODS

A cohort of 25 unrelated adenomatous polyposis families of Greek origin has been selected. Genetic testing included direct sequencing of APC and MUTYH genes. APC gene was also checked for large genomic rearrangements by MLPA.

RESULTS

Analysis of the APC gene performed in a Greek cohort of twenty five FAP families revealed eighteen different germline mutations in twenty families (80%), four of which novel. Mutations were scattered between exon 3 and codon 1503 of exon 15, while no large genomic rearrangements were identified.

CONCLUSION

This concise report describes the spectrum of all APC mutations identified in Greek FAP families, including four novel mutations. It is concluded that the Greek population is characterized by genetic heterogeneity, low incidence of genomic rearrangements in APC gene and lack of founder mutation in FAP syndrome.

Polishing the crystal ball: knowing genotype improves ability to predict desmoid disease in patients with familial adenomatous polyposis

INTRODUCTION

Desmoid disease occurs in one third of patients with familial adenomatous polyposis. Patients may be protected by changing surgical strategy. We designed a formula to predict desmoid risk and tested the value of adding genotype to the formula.

METHODS

A desmoid risk factor was calculated by summing points awarded for gender (male = 1, female = 3), extracolonic manifestations (nil = 1, one = 2, >one = 3), and family history of desmoids (negative = 1, one relative = 2, more than one relative = 3). Performance of the score with and without genotype (5' 1309 = 1, 1309-1900 = 2, 3' 1900 = 3) was analyzed.

RESULTS

There were 839 patients (138 desmoids) without genotype and 154 (30 desmoids) with genotype. The mean desmoid risk factor score of patients without desmoids (no genotype) was 4.7 (+/-1.4 SD) and for patients with desmoid the desmoid risk factor was 6.0 (+/-1.7, P < 0.001). Corresponding data for patients with genotype was 6.1 +/- 1.3 (no desmoids) and 8.4 +/- 1.8 with desmoids (P < 0.001). Of patients without genotype, 648 patients were at low risk and 9.9% had desmoid disease, 178 patients were at medium risk and 34% had desmoids, and 10 patients were at high risk and all had desmoids. Of those with genotype information, 83 patients were at low risk and 5% had desmoids, 52 patients were at medium risk and 21% had desmoids, and 18 patients were at high risk and 83% had desmoids.

CONCLUSION

The desmoid risk factor identifies patients with various levels of risk for developing desmoid disease, and can be used to plan surgical strategies designed to minimize desmoid risk.

APC somatic mosaicism in a patient with Gardner syndrome carrying the E1573X mutation: report of a case

We report a case of somatic APC mosaicism in an person with a clinical diagnosis of Gardner syndrome with features of attenuated polyposis coli and with an uninformative family history. In initial screening for APC mutations, the germline mutation E1573X was detected in a lower proportion than that predicted by a heterozygous mutation indicating the presence of somatic mosaicism. Pyrosequencing confirmed this hypothesis and quantified the presence of the mutation in approximately 18% of the blood lymphocytes. Mutational analysis performed in the offspring revealed a fully heterozygous E1573X mutation in 2 of the 3 individuals tested. The milder colonic phenotype exhibited by the index patient could be a consequence of the presence of the mosaicism in the colon mucosa. The detection of the mutation in other tissues and in the offspring suggests that it may have occurred early during embryogenesis, before the separation of the embryonic layers. The E1573X mutation is the most distal mutation in the APC sequence reported to date as a mosaic and, interestingly, in the context of Gardner syndrome with extensive extracolonic features. Mosaicism is an important consequence of de novo APC mutations and it should be considered in the management of apparently sporadic or de novo cases, particularly in the evaluation of the risk of siblings and offspring.

May the APC gene somatic mutations in tumor tissues influence the clinical features of Chinese sporadic colorectal cancers?

The APC gene plays an important role in colorectal carcinogenesis. The impact of APC mutations on the clinical features in sporadic CRC remains to be uncovered. The APC gene was screened for mutations with systematic analysis techniques including DHPLC, PTT, MLPA and DNA sequencing in 43 Chinese sporadic CRC patients. Twenty nine somatic mutations (in 17 different types) in APC gene were found in 18 of 43 sporadic CRC patients. Of those, nine were novel mutations. Higher frequency of somatic APC mutations was found in younger CRC patients than that in elder ones. The biallelic somatic mutations of APC gene were identified in four CRC patients whose tumors had more invasive clinical features. The nonsense mutation Arg1114X in APC gene was found in five of 43 CRC tumor tissues. A higher cancer metastasis rate was uncovered in CRC patients with this mutation. The somatic mutations of APC gene may influence the clinical features of sporadic CRC. Arg1114X in APC gene, as a hot spot mutation in Chinese CRC, may predispose to the cancer metastasis of sporadic CRC.

[Hereditary colorectal cancer]

One of the main challenges in the clinical management of familial colorectal cancer (CRC) remains the overlap of syndromes with different underlying genetic causes and the differentiated risk management of colorectal and associated malignancies. The Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC) is characterized by the development of colorectal, endometrial, gastric and other cancers and is caused by a mutation in one of the mismatch repair (MMR) genes. Microsatellite instability (MSI) and/or immunohistochemistry (IHC) are important prognostic factors and may predict the response to chemotherapy. Familial adenomatous polyposis (FAP) may be seen as a counterpart to Lynch syndrome, responsible for <1% of all CRC cases. Recently the MUTYH gene has been identified as a further polyposis gene. The associated disorder has been termed MYH-associated polyposis (MAP) and displays an autosomal recessive pattern of inheritance. For clinical management, distinguishing between Lynch syndrome, attenuated FAP and MAP is important for risk assessment, surveillance recommendations and indication for prophylactic surgery.

Prognostic and therapeutic implications of Apc mutations in colorectal cancer

The adenomatous polyposis coli gene (Apc) is mutated in most colorectal cancers. The multifunctional character of the Apc protein in the regulation of beta-catenin-mediated gene transcription and cytoskeletal proteins has been well described. An important question is how this protein affects the behaviour of cells within a tumour and how its mutational status influences the prognosis for these tumours. Here we provide an overview of the functions of Apc and examine how this information can be used in the prognosis and development of directed therapy in colorectal cancer.

Mutational screening of the APC gene in Chilean families with familial adenomatous polyposis: nine novel truncating mutations

PURPOSE

Familial adenomatous polyposis is characterized by the development of hundreds of adenomatous polyps located mainly in the colon and rectum. Patients with familial adenomatous polyposis who do not receive treatment will develop cancer before aged 40 years. This disease is caused by germline mutations in the adenomatous polyposis coli gene. Different studies have shown a correlation between the location of the mutation and the clinical phenotype, such as the grade of severity and/or the presence of extracolonic manifestations, such as desmoid tumors. This study was designed to identify germline mutation in the adenomatous polyposis coli gene in Chilean families with familial adenomatous polyposis.

METHODS

We examined the adenomatous polyposis coli gene in 24 Chilean families with familial adenomatous polyposis. The adenomatous polyposis coli gene was screened for mutations combining single strand conformation polymorphism technique, protein truncation test, and DNA sequencing.

RESULTS

We detected 17 different truncating mutations in 21 of 24 families (87.5 percent); 9 of these were novel. Fourteen mutations were detected in exon 15, being the most frequent c.3,927_3,931delAAAGA, found in 3 of 21 families (14 percent). Eight families (33 percent) showed at least one patient affected with desmoid tumors, presenting mutations between codons 849 and 1,533. Interestingly, two mutations, c.3,632dupA and c.3,783_3,784delTT, leading into a truncating protein at codons 1,216 and 1,274, were associated with almost 100 percent penetrance for desmoid tumors among relatives.

CONCLUSIONS

We achieved 87 percent mutation detection rate in adenomatous polyposis coli gene; more than 50 percent of them were novel. The high percentage of novel mutations found may be because of the genetic composition of the Chilean population, which is an admixture of Amerindian and Spaniards, and the scarce information in the literature about similar populations.

Somatic APC mosaicism: a frequent cause of familial adenomatous polyposis (FAP)

Somatic mutational mosaicism presents a challenge for both molecular and clinical diagnostics and may contribute to deviations from predicted genotype-phenotype correlations. During APC mutation screening in 1,248 unrelated patients with familial adenomatous polyposis (FAP), we identified 75 cases with an assumed or confirmed de novo mutation. Prescreening methods (protein truncation test [PTT], DHPLC) indicated the presence of somatic mosaicism in eight cases (11%). Sequencing of the corresponding fragments revealed very weak mutation signals, pointing to the presence of either nonsense or frameshift mutations at low level. All mutations were confirmed and quantified by SNaPshot analysis: in leukocyte DNA from the eight patients, the percentage of mosaicism varied between 5.5% and 77%, while the proportion of the mutation in DNA extracted from adenomas of the respective patient was consistently higher. The eight mutations identified as mosaic are localized within codons 216-1464 of the APC gene. According to the known genotype-phenotype correlation, patients with mutations in this region exhibit typical or severe FAP. However, six of the eight patients presented with an attenuated or atypical polyposis phenotype. Our data demonstrate that in a fraction of FAP patients the causative APC mutation may not be detected due to weak signals or somatic mosaicism that is restricted to tissues other than blood. SNaPshot analysis was proven to be an easy, rapid, and reliable method of confirming low-level mutations and evaluating the degree of mosaicism. Some of the deviations from the expected phenotype in FAP can be explained by the presence of somatic mosaicism.

How the I1307K adenomatous polyposis coli gene variant contributes in the assessment of risk of colorectal cancer, but not stomach cancer, in a Turkish population

Germline and somatic truncating mutations of the adenomatous polyposis coli gene (APC) are thought to initiate colorectal tumor formation in familial adenomatous polyposis syndrome and sporadic colorectal carcinogenesis, respectively. Recently, an isoleucine-lysine polymorphism at codon 1307 (I1307K) of the APC gene has been identified in 6-7% of the Ashkenazi Jewish population. To assess the risk of this common APC allelic variant in colorectal carcinogenesis, a cohort of unselected Turkish subjects with stomach or colorectal cancer (or both) was analyzed for the APC I1307K polymorphism. Genomic DNA was extracted from patients by obtaining all stomach and colon malign polipose tissues using nuclei lysis methods. Detection of the I1307K mutation was performed using the commercial Pronto APC kit according to the manufacturer's instructions. The APC I1307K allele was identified in 7 of 57 stomach carcinoma patients (12.3%; P > 0.05) and 30 of 56 colon carcinoma patients (53.6%; P < 0.05) using antigen-anticor interaction methods. Comparing the frequencies of the two separate population control groups, the APC I1307K allele is associated with an estimated relative risk of 1.9 for colorectal neoplasia. Furthermore, APC I1307K carriers had greater numbers of adenomas and colorectal cancers per patient than noncarriers. The conclusion is that the APC I1307K variant leads to increased adenoma formation and colorectal cancer. The estimated relative risk for carriers may justify specific clinical screening for Turkish people expected to harbor this allele, and genetic testing in the long term may significantly promote colorectal cancer prevention in this population.

Germline mutations in APC and MUTYH are responsible for the majority of families with attenuated familial adenomatous polyposis

A small fraction of families with familial adenomatous polyposis (FAP) display an attenuated form of FAP (AFAP). We aimed to assess the presence of germline mutations in the MUTYH and adenomatous polyposis coli (APC) genes in AFAP families and to compare the clinical features between the two causative genes. Families with clinical AFAP were selected from the Dutch Polyposis Registry according to the following criteria: (a) at least two patients with 10-99 adenomas diagnosed at age >30 years or (b) one patient with 10-99 adenomas at age >30 years and a first-degree relative with colorectal cancer (CRC) with a few adenomas, and, applying for both criteria, no family members with more than 100 polyps before the age of 30 years. All probands were screened for germline mutations in the APC and MUTYH genes. Twenty-five of 315 Dutch families with FAP (8%) met our criteria for AFAP. These families included 146 patients with adenomas and/or CRC. Germline APC mutations were identified in nine families and biallelic MUTYH mutations in another nine families. CRC was identified at a mean age of 54 years (range 24-83 years) in families with APC and at 50 years (range 39-70 years) in families with MUTYH (p = 0.29). APC and biallelic MUTYH mutations are responsible for the majority of AFAP families. Based on our results and those reported in the literature, we recommend colonoscopy once every 2 years in AFAP families, starting surveillance from the late teens in APC mutation carriers and from age 20-25 years in biallelic MUTYH mutation carriers.

Germline MYH mutations in a clinic-based series of Canadian multiple colorectal adenoma patients

OBJECTIVES

MYH is a member of the DNA base excision repair (BER) pathway and mutations of this gene predispose to the development of colorectal neoplasia in an autosomal recessive transmission pattern. Our objective was to determine the significance of MYH mutations in a series of Canadian patients with multiple adenomas.

METHODS

We screened for germline MYH mutations (by dHPLCO) in 20 clinic-based multiple adenoma patients who were adenomatous polyposis coli (APC) mutation-negative. Suspected mutations were confirmed by sequence analysis.

RESULTS

Six of 20 (30%) patients carried pathogenic biallelic MYH mutations, 1 Y165C homozygote and 5 compound heterozygotes of other sequence variants. We identified three novel variants, Q377X, 1314delA, and P281L, which are likely pathogenic. Twenty-nine relatives of the Y90X/1103delC compound heterozygous carrier were also screened for germline MYH mutations, and 1 homozygous and 14 heterozygous carriers were identified.

CONCLUSIONS

Among patients with multiple adenomas, biallelic MYH mutations account for approximately 30% of APC mutation negative cases and two thirds of these carry mutations other than the "common" Y165C and G382D variants. Clinical screening algorithms which focus only on the Y165C and G382D alleles are inadequate since additional pathogenic mutations may be identified by screening the entire gene.

Familial adenomatous polyposis: The practical applications of clinical and molecular screening

Familial adenomatous polyposis (FAP) is an autosomal dominant condition mostly due to a mutation of the APC gene on the chromosome 5q. Carriers have an almost 100% chance of developing colorectal cancer after having multiple (typically 100s to 1000s) of adenomatous polyps. It is usually readily identified through this phenotype of multiple adenomas. Correlations between the location of the family-specific mutation on the APC gene and clinical manifestations of the disease are of some assistance in clinical management, though there is heterogeneity in clinical course even between family members with the same mutation. FAP is important to recognize, as there are disease-specific management implications with respect to offering mutational analysis of the APC (and perhaps other) genes for predictive testing of other family members, endoscopic diagnostic procedures, surveillance planning, and surgical management. Extra-colonic manifestations, including duodenal polyposis, desmoid disease and other tumours, can dominate clinical care after colectomy. The inheritable and lethal nature of the disease, together with the availability of effective treatment strategies, makes a sensitive clinical and psychosocial approach important to maximize compliance and good outcomes for all members of affected families.

Familial adenomatous polyposis (FAP): genotype correlation to FAP phenotype with osteomas and sebaceous cysts

Gardner syndrome is characterized by the triad of colorectal adenomas, soft and hard tissue tumors. This disorder was regarded as a separate disease until the identification of the APC gene when it was recognized that mutations in the APC gene were the underlying cause of both Gardner syndrome and familial adenomatous polyposis (FAP). The present study aimed at examining whether a particular APC genotype could be delineated in FAP patients with benign extracolonic manifestations: sebaceous cysts and/or osteomas. A questionnaire was sent to all Danish FAP patients (N = 234) asking for occurrence of sebaceous cysts and palpable osteomas. Medical records later verified positive findings, when possible. The results for each patient were correlated to the position of his or her mutation in the APC gene. Positive participation compliance was 77% (N = 180), and in 105 of these patients the pathogenic APC mutation was known. Palpable osteomas were reported in 17 of the patients in whom a pathogenic mutation had been identified. Osteomas were only identified in patients with mutations between codon 767 and 1513, a gene area also associated with congenital hypertrophy of the retinal-pigmented epithelium (CHRPE) and hepatoblastoma. Sebaceous cysts were reported in 51% of the patients, and their APC mutations were evenly distributed in the gene with no particular hotspot. Osteomas appeared most frequently in patients with sebaceous cysts, odds ratio 6.6, P < 0.001. The study provides molecular evidence that Gardner syndrome is a variant of FAP and essentially obsolete in clinical practice.

Evolution of the nomenclature for the hereditary colorectal cancer syndromes

The hereditary forms of colorectal cancer have been given many names historically as the manifestations have been gradually understood. Lynch syndrome has had several names, most prominently 'Hereditary Nonpolyposis Colorectal Cancer' or HNPCC. Clarification of the genetic basis and full phenotypic expression of this disease mandates a more clinically useful name that clarifies the consideration of non-colonic cancers in a family history, and unifies the diagnosis around the germline mutation in a DNA mismatch repair (MMR) gene. The term 'Lynch syndrome' is proposed for the autosomal dominant disease caused by a germline mutation in a DNA MMR gene.

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.

Generation of a unique strain of multiple intestinal neoplasia (Apc(+/Min-FCCC)) mice with significantly increased numbers of colorectal adenomas

The relevance of the Apc(+/Min) mouse model in the study of human colorectal cancer remains uncertain due to the predominance of small intestinal adenomas and few, if any, colorectal adenomas. A new strain of Apc(+/Min) mice (Apc(+/Min-FCCC)) with significantly greater numbers of colorectal adenomas has been generated and characterized. Male C57BL/6J-Apc(+/Min) mice (the Jackson Laboratory, Bar Harbor, ME) were crossed with wild-type (Apc(+/+)) C57BL/6J females from an independent colony at this institution (offspring=Apc(+/Min-FCCC)) and 233 animals were evaluated over 20 generations. In order to determine the contribution of genetics to the enhanced colorectal adenoma phenotype, breeding pairs (Apc(+/Min) male x wild type female C57BL/6J) were purchased from the Jackson Laboratory and offspring (Apc(+/Min-JAX)) were maintained in our facility under identical conditions (n=98). Animals were fed Purina Rodent chow (#5013) diet containing 5% fat. The entire intestinal tract was examined histopathologically in both strains. Both the Apc and Pla2g2a (candidate for Mom1) genes were sequenced and found to be identical for both the Apc(+/Min-FCCC) and Apc(+/Min-JAX) mouse strains. The multiplicity of colorectal adenomas in the Apc(+/Min-FCCC) mice was much higher than reported in the literature and significantly greater than the multiplicity of colorectal adenomas in Apc(+/Min-JAX) mice maintained in our facility (P=0.01). Apc(+/Min-FCCC) had a significantly greater incidence of rectal prolapse (P = 0.02) and small intestinal adenocarcinomes (P=0.001), and multiplicity of small intestinal adenocarcinomas (P=0.001) compared to Apc(+/Min-JAX) mice. Male Apc(+/Min-FCCC) mice had significantly greater numbers of colorectal adenomas compared to female Apc(+/Min-FCCC) mice (P=0.0002), as did male Apc(+/Min-JAX) mice vs. female Apc(+/Min-JAX) mice (P< 0.0001). These results allow us to conclude: (1) Apc(+/Min-FCCC) mice are unique in that they develop significantly greater numbers of colorectal adenomas and small intestinal cancers, and a significantly greater incidence of small intestinal cancers and rectal prolapse than Apc(+/Min-JAX) mice. (2) This study represents the first report of a significant gender difference in multiplicity of colorectal adenomas. (3) Differences between Apc(+/Min-FCCC) and Apc(+/Min-JAX) mice in currently undefined genetic modifiers may contribute to the enhanced colorectal phenotype. (4) The Apc(+/Min-FCCC) strain is highly suited for the investigation of colorectal neoplastic disease and chemoprevention studies.

Familial adenomatous polyposis: experience from a study of 1164 unrelated german polyposis patients

The autosomal-dominant precancerous condition familial adenomatous polyposis (FAP) is caused by germline mutations in the tumour suppressor gene APC. Consistent correlations between the site of mutations in the gene and clinical phenotype have been published for different patient groups. We report our experiences of APC mutation analysis and genotype-phenotype correlations in 1166 unrelated polyposis families and discuss our results in the light of literature data. We show that the mutation detection rates largely depend on the family history and clinical course of the disease. We present a list of 315 different point mutations and 37 large deletions detected in 634 of the 1166 index patients. Our results confirm previously published genotype-phenotype correlations with respect to the colorectal phenotype and extracolonic manifestations. However, 'exceptions to the rule' are also observed, and possible explanations for this are discussed. The discovery of autosomal-recessive MUTYH-associated polyposis (MAP) as a differential diagnosis to FAP implies that some results have to be reinterpreted and surveillance guidelines in the families have to be reevaluated.

Adenomatous polyposis families that screen APC mutation-negative by conventional methods are genetically heterogeneous

PURPOSE

One third of families with classical adenomatous polyposis (FAP), and a majority of those with attenuated FAP (AFAP), remain APC mutation-negative by conventional methods. Our purpose was to clarify the genetic basis of polyposis and genotype-phenotype correlations in such families.

PATIENTS AND METHODS

We studied a cohort of 29 adenomatous polyposis families that had screened APC mutation-negative by the protein truncation test, heteroduplex analysis, and exon-specific sequencing. The APC gene was investigated for large genomic rearrangements by multiplex ligation-dependent probe amplification (MLPA), and for allelic mRNA expression by single nucleotide primer extension (SNuPE). The AXIN2 gene was screened for mutations by sequencing.

RESULTS

Four families (14%) showed a constitutional deletion of the entire APC gene (three families) or a single exon (one family). Seven families (24%) revealed reduced or extinct mRNA expression from one APC allele in blood, accompanied by loss of heterozygosity in the APC region in six (75%) of eight tumors. In 15 families (52%), possible APC involvement could be neither confirmed nor excluded. Finally, as detailed elsewhere, three families (10%) had germline mutations in genes other than APC, AXIN2 in one family, and MYH in two families.

CONCLUSION

"APC mutation-negative" FAP is genetically heterogeneous, and a combination of MLPA and SNuPE is able to link a considerable proportion (38%) to APC. Significant differences were observed in clinical manifestations between subgroups, emphasizing the importance of accurate genetic and clinical characterization for the proper management of such families.

Familial adenomatous polyposis: aberrant splicing due to missense or silent mutations in the APC gene

Familial adenomatous polyposis (FAP) is caused by germline mutations in the tumor suppressor gene APC. To date, the relevance of rare exonic single-base substitutions at nucleotide positions close to splice sites that are predicted to result in missense or silent (SNP) variants or substitutions in introns at splice-site positions that are not highly conserved has not been systematically examined in FAP patients. In 34 index patients, we identified 26 different heterozygous single-base substitutions at or close to the splice sites. We characterized five exonic mutations in exon 4 (c.423G>T), exon 14 (c.1956C>T, c.1957A>G, and c.1957A>C), and exon 15 (c.1959G>A) by transcript analysis and by splice-prediction programs (BDGP, SpliceSiteFinder, and ESEfinder). The splicing patterns of these variants were compared to those of 16 different substitutions at highly or less-conserved intronic splice-site positions, and to normal controls. In addition, we analyzed cosegregation of the variants with affected family members and examined the genotype-phenotype correlation. We could demonstrate that the four unclear variants in exon 4 and 14 that are predicted to result in missense or silent mutations in fact lead to complete exon skipping due to aberrant splicing; one possible explanation for this observed effect might be the disruption of exonic splicing enhancer (ESE) motifs. In contrast, the substitution at the first position of exon 15 seems to actually be a silent variant. We present the first systematic evaluation of different single-base substitutions in APC at or close to splice sites at transcript level. We show that the consequence of exonic mutations cannot be evaluated only by the predicted change in amino acid sequence but rather by the change at DNA level. The functional analysis of variants with unknown pathogenic effect plays an important role in increasing the mutation detection rate and achieving validation of predictive testing.

Colorectal cancer in two pre-teenage siblings with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder that characteristically presents with colon cancer in early adult life. We describe a Pakistani FAP family in which two sons had an unusually early manifestation of colorectal cancer. The index patient presented at 11 years of age with abdominal pain, rectal bleeding and iron deficiency anaemia. Colonoscopy showed that the colon was carpeted with a myriad of polyps. Oesophago-gastric and duodenal endoscopy revealed that polyps had also developed in the duodenum. Multiple biopsies indicated neoplastic lesions. The patient underwent a proctocolectomy and endoscopic duodenal mucosectomy. The diagnosis of an adenocarcinoma of the colon and further adenomatous polyps with low-grade and high-grade dysplasia was confirmed by histology. Family screening including a blood test for anaemia and bowel examination revealed that his 12-year-old brother was also affected.

CONCLUSION

Children with familial adenomatous polyposis are at risk for colon cancer and emphasise the need for early tumour recognition. Gastrointestinal symptoms in children should be thoroughly evaluated and standard screening for colonic polyposis should be performed in all individuals with a positive family history and/or known mutations in cancer-associated genes, particularly in children who are under 10 years of age.

Highly penetrant hereditary cancer syndromes

The past two decades have brought many important advances in our understanding of the hereditary susceptibility to cancer. Approximately 5-10% of all cancers are inherited, the majority in an autosomal dominant manner with incomplete penetrance. While this is a small fraction of the overall cancer burden worldwide, the molecular genetic discoveries that have resulted from the study of families with heritable cancer have not only changed the way these families are counselled and managed, but have shed light on molecular regulatory pathways important in sporadic tumour development as well. In this review, we consider 10 of the more highly penetrant cancer syndromes, with emphasis on those predisposing to breast, colon, and/or endocrine neoplasia. We discuss the prevalence, penetrance, and tumour spectrum associated with these syndromes, as well as their underlying genetic defects.

Genetic testing and phenotype in a large kindred with attenuated familial adenomatous polyposis

BACKGROUND & AIMS

An attenuated form of familial adenomatous polyposis has been described, but the phenotype remains poorly understood.

METHODS

We performed genetic testing on 810 individuals from 2 attenuated familial adenomatous polyposis kindreds harboring an identical germline adenomatous polyposis coli gene mutation. Colonoscopy was performed on mutation-positive persons.

RESULTS

The disease-causing mutation was present in 184 individuals. Adenomatous polyps were present in 111 of 120 gene carriers who had colonoscopy at an average age of 41 years. The median number of adenomas was 25 (range, 0-470), with striking variability of polyp numbers and a proximal colonic predominance of polyps. Colorectal cancer occurred in 27 mutation carriers (average age, 58 years; range, 29-81 years), with 75% in the proximal colon. The cumulative risk of colorectal cancer by age 80 was estimated to be 69%. An average of 3.4 recurrent polyps (range, 0-29) were found in the postcolectomy rectal remnant over a mean of 7.8 years (range, 1-34 years), with 1 rectal cancer.

CONCLUSIONS

This investigation shows that attenuated familial adenomatous polyposis in the kindreds examined shows a much smaller median number of polyps than typical familial adenomatous polyposis, a wide variability in polyp number even at older ages, and a more proximal colonic location of polyps and cancer, yet it is associated with an extremely high risk of colon cancer. The phenotype of attenuated familial adenomatous polyposis mimics typical familial adenomatous polyposis in some cases but in others is difficult to distinguish from sporadic adenomas and colorectal cancer, thus making genetic testing particularly important.

Intron 4 mutation in APC gene results in splice defect and attenuated FAP phenotype

The adenomatous polyposis coli (APC) protein is a tumor suppressor frequently involved in the development of inherited and sporadic colon cancers. Somatic mutations of the APC gene are found in 80% of all colon cancers. Inherited mutations result in familial adenomatous polyposis (FAP) as well as an attenuated form of this syndrome. FAP is characterized by the early age onset of hundreds to thousands of colonic adenomatous polyps and a virtual certainty of colon cancer unless the colon is removed. The attenuated form of FAP (AFAP) is characterized by fewer adenomas, later onset of adenomas and cancer, and a decreased lifetime cancer risk. We report a 37-year-old man with a history of more than 50 colonic adenomatous polyps, located predominately in the right colon. An insertion of a single thymidine between the second and third base pairs of intron 4 of the APC gene was identified (c.531+2_531+3insT). Monoallelic hybrid cells harboring a single copy of human chromosome 5 were generated from patient lymphoblasts. Sequencing of the APC cDNA product from these cells revealed a single RNA transcript with aberrant splicing in the mutant mRNA whereby exon 4 is deleted. The translational reading frame is shifted after codon 140 and a translational stop is generated predicting a truncated protein of 147 amino acids, thus indicating that the intronic mutation is disease causing. The lack of a secondary transcript from the mutant allele suggests that incomplete exon skipping is not the molecular mechanism behind the attenuated phenotype.

Profuse familial adenomatous polyposis with an adenomatous polyposis coli exon 3 mutation

The attenuated form of familial adenomatous polyposis coli (AAPC) is associated with mutations in the adenomatous polyposis coli (APC) gene which cluster in the 5' region of the gene. It has been proposed that a 'genotype-phenotype boundary' exists at codons 159-163, and mutations that are 5' of this boundary will produce AAPC. Herein we document a three-generation family with an exon 3 mutation well to the 5' side of the proposed boundary, in which two affected individuals have had, in their 40s, a profuse form of familial adenomatous polyposis coli. We conclude that the codon 159-163 'boundary' is indicative rather than definitive. These two patients also had postoperative intra-abdominal adhesions, severely so in one.

Multiple approach to the exploration of genotype-phenotype correlations in familial adenomatous polyposis

PURPOSE

Familial adenomatous polyposis (FAP), caused by a mutation in the APC gene, is a colorectal cancer predisposition syndrome associated with several other clinical conditions. The severity of the FAP is related to the position of the inherited mutation in the APC gene. We analyzed a large series of FAP patients to identify associations among major clinical manifestations and to correlate the mutation site with specific disease manifestations.

MATERIALS AND METHODS

APC mutations were identified in 953 FAP patients from 187 families. We used unconditional logistic regression models and a method involving generalized estimating equations to investigate the association between genotype and phenotype. We used multiple correspondence analysis to represent the interrelationships of a multiway contingency table of the considered variables.

RESULTS

APC germline mutations were located between codons 156 and 2011 of the APC gene. Mutations spanning the region between codons 543 and 1309 were variable, but strongly associated with congenital hypertrophy of retinal pigment epithelium. Mutations between codons 1310 and 2011 were associated with a six-fold risk of desmoid tumors relative to the low-risk reference region (159 to 495). Mutations at codon 1309 were associated with early development of colorectal cancer. Mutations between codons 976 and 1067 were associated with a three- to four-fold increased risk of duodenal adenomas. The cumulative frequency of extracolonic manifestations was highest for mutations between codons 976 and 1067, followed by mutations between 1310 and 2011.

CONCLUSION

Analysis of the relation between APC mutation site and phenotype identifies subgroups of FAP patients at high risk for major extracolonic disease, which is useful for surveillance and prevention.

Preventive surgery for colon cancer in familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer syndrome

BACKGROUND

A better understanding of the molecular basis of hereditary colorectal cancer syndromes such as hereditary nonpolyposis colorectal cancer syndrome (HNPCC) and familial adenomatous polyposis (FAP) has profound consequences for both the diagnosis and (prophylactic) treatment of (pre)malignant neoplastic lesions.

DISCUSSION

Sequence analysis of the underlying genes for these conditions and the detection of disease-causing genetic alterations in an index patient enable predictive testing for individuals at risk within an affected family. However, the clinical implications of predictive molecular testing depend on the overall penetrance and variability in the expression of pathogenic mutations. The extent of these parameters differs considerably among the various known hereditary colorectal cancer syndromes. Hence the integration of genetic information into the daily surgical practice remains challenging.

CONCLUSIONS

This review provides an update on the indications for family assessment, purpose and limitations of the genetic testing and resulting recommendations for prophylactic surgery in FAP and HNPCC.

APC, beta-Catenin and hTCF-4; an unholy trinity in the genesis of colorectal cancer

Mutations in APC have been identified in up to 80% of 'classic' sporadic colorectal cancers. Although the APC gene was first sequenced over a decade ago, new functions are still being described and its importance in the genesis of colorectal cancer continues to increase. The current focus of attention is on the APC/beta-Catenin/TCF signal transduction pathway as the main effector mechanism, and recent work has also implicated this pathway in the aetiology of the minority of CRCs that develop through mismatch repair. At the same time, new evidence on the interactions of APC with the cytoskeleton and the demonstration of a nuclear export function in the protein have shown that it has multiple additional roles in colorectal carcinogenesis. Thus this is an area that benefits from further review of the ever expanding literature.

Effect of sulindac treatment for attenuated familial adenomatous polyposis with a new germline APC mutation at codon 161: report of a case

INTRODUCTION

Patients with familial adenomatous polyposis develop colorectal cancers if left untreated. As indicated in patients with familial adenomatous polyposis, prophylactic colectomy has been recommended even in a milder colonic phenotype referred to as attenuated familial adenomatous polyposis. However, therapeutic strategies in attenuated familial adenomatous polyposis are still controversial.

METHODS

We report a patient with attenuated familial adenomatous polyposis who has been treated with sulindac for five years. During the period of observation, she has been carefully followed up by chromoscopic and radiographic surveillance. Immunohistochemical study for cyclooxygenase-2 and genetic analysis in the adenomatous polyposis coli gene was also performed.

RESULTS

Continuous administration of sulindac resulted in obvious regression of both colorectal adenomatous polyps and gastric fundic gland polyps, and no cancers developed during the observation period. Immunohistochemical study showed the decrease of cyclooxygenase-2-positive epithelial cells in colorectal polyps by the treatment. The genetic analysis revealed a C to A substitution at nucleotide 481 of her germline adenomatous polyposis coli gene, which resulted in a nonsense mutation at codon 161.

CONCLUSIONS

Our case suggests that treatment with sulindac accompanied by intensive colonoscopic surveillance may be a choice of management for attenuated familial adenomatous polyposis.

Genetic insights into familial cancers-- update and recent discoveries

While the vast majority of cancers are believed to occur sporadically, most forms of cancer, both adult and paediatric, have a hereditary equivalent. In the case of adult malignancies, these include hereditary breast and ovarian cancer and syndromes such as the multiple endocrine neoplasias types 1 and 2 characterised by specific tumours of the endocrine gland system. In the case of paediatric malignancies, these include syndromes such as retinoblastoma and Wilms tumour. In a little over a single decade, we have seen a tremendous increase in the knowledge of the primary genetic basis of many of the familial cancer syndromes. The majority of familial syndromes are inherited as autosomal dominant traits including hereditary colon cancer and familial malignant melanoma, however, the genetics behind autosomal recessive disorders such as Bloom syndrome and Fanconi anaemia are also being elucidated. A third mode of inheritance less well understood in the setting of familial cancer is that of imprinting recently observed in a subset of families with inherited paraganglioma. In this review, we discuss 31 genes inherited in an autosomal dominant manner associated with 20 familial cancer syndromes. Genes inherited in an autosomal recessive manner linked to familial cancer syndromes are also discussed. The identification of genes associated with familial cancer syndromes has in some families enabled a 'molecular diagnosis' that complements clinical assessment and allows directed cancer surveillance for those individuals determined to be at-risk of disease.

Attenuated APC alleles produce functional protein from internal translation initiation

Some truncating mutations of the APC tumor suppressor gene are associated with an attenuated phenotype of familial adenomatous polyposis coli (AAPC). This work demonstrates that APC alleles with 5' mutations produce APC protein that down-regulates beta-catenin, inhibits beta-catenin/T cell factor-mediated transactivation, and induces cell-cycle arrest. Transfection studies demonstrate that cap-independent translation is initiated internally at an AUG at codon 184 of APC. Furthermore, APC coding sequence between AAPC mutations and AUG 184 permits internal ribosome entry in a bicistronic vector. These data suggest that AAPC alleles in vivo may produce functional APC by internal initiation and establish a functional correlation between 5' APC mutations and their associated clinical phenotype.

Molecular diagnosis of familial adenomatous polyposis (FAP): genotyping of adenomatous polyposis coli (APC) alleles by MALDI-TOF mass spectrometry

OBJECTIVES

Familial adenomatous polyposis (FAP) is an autosomal dominantly inherited colorectal cancer predisposition syndrome caused by germ line mutations in the adenomatous polyposis coli gene (APC). For prophylactic colectomy, timely identification of patients at risk is urgent. Here, matrix assisted laser desorption ionization - time of flight - mass spectrometry (MALDI-TOF-MS) genotyping is offered for an efficient molecular diagnosis of APC germline mutations.

DESIGN AND METHODS

The four most frequent APC germ line mutations (three deletions, one point mutation) were genotyped by allele specific elongation and termination of extension primers. The extension products generated were analyzed by MALDI-TOF-MS.

RESULTS

Following PCR amplification and allele specific primer extension reactions MALDI-TOF-MS allowed the unambiguous identification of informative nucleic acid fragments corresponding to distinct genotypes or mutants even in duplex assays. Results were confirmed by DNA-sequencing.

CONCLUSIONS

Due to its high molecular resolution and accuracy, this method is highly suitable as an alternative for clinical APC genotyping.

Gene mutation as a target for early detection in cancer diagnosis

The increasing number of genetic aberrations implicated in the development of human cancer has prompted a search to detect them at the earliest possible stage of their formation. Of the many such genetic changes identified thus far, relatively few meet the standard for markers in early diagnosis and prognosis, namely that the genetic modifications occur during the early onset phase of cancer development. Parallel to the increasing number of such genes is the growing availability of technologies using more powerful and cost-efficient methods that enable mass screening for genetic alterations. The purpose of this review is to summarize the currently available genes that can serve as markers for early detection of cancers and methods that allow their detection.