Variable phenotype of familial adenomatous polyposis in pedigrees with 3' mutation in the APC gene

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.

Approach to Familial Predisposition to Colorectal Cancer

The traditional approach of one-size-fits-all for colorectal cancer has been replaced by personalized interventions to an individual's unique genetic, molecular, and environmental profile, seeking to identify high-risk individuals who would benefit from individualized screening and surveillance. This change in approach is due, in part, to emerging technologies, such as next-generation DNA sequencing.

The Second Allele: A Key to Understanding the Timing of Sporadic and Hereditary Colorectal Tumorigenesis

Our understanding of the molecular basis of colorectal neoplasia is derived from Mendelian genetics, with tumor suppressor genes contributing more to the deregulation of growth than oncogenes. In patients with hereditary syndromes, expression of one allele of a key tumor suppressor gene is absent at birth. The loss of the expression of the second allele precipitates tumorigenesis. However, there are multiple ways in which the expression of the second allele of a tumor suppressor gene is lost. Here, we review these ways and their possible effect on phenotype.

Approach to screening for Familial Adenomatous Polyposis (FAP) in a cohort of 226 patients with Desmoid-type Fibromatosis (DF): experience of a specialist center in the UK

INTRODUCTION

Desmoid-type fibromatosis (DF) are locally infiltrative, non-metastasizing tumours associated with significant morbidity and mortality if located intra-abdominally, retroperitoneally or in head and neck localisation. They are mostly sporadic, due to somatic CTNNB1 mutations. Alternatively, they can be associated with germline pathogenic variants in APC causing Familial Adenomatous Polyposis (FAP). Germline APC variants and somatic CTNNB1 mutations are mutually exclusive.

AIMS AND METHODS

We conducted a retrospective descriptive analysis of patients with DF seen at the Royal Marsden NHS Foundation Trust Sarcoma Unit in London. We aimed to describe the methods of screening for FAP in patients with DF from a specialist unit. Patients diagnosed between 1992 and 2020 were selected from the prospectively maintained Sarcoma Unit database.

RESULTS

226 patients were identified and 67% (n = 152) were female. Median age at diagnosis was 37.5 (range 2-81) years. Tumour localisation was limbs/pelvis in 30.9% (N = 70), intra-abdominal 16.8% (N = 38), abdominal wall 23.5% (N = 53), thorax 18.6% (N = 42), head and neck 3.1% (N = 7) and vertebral/paravertebral 7.1% (N = 16). Colonoscopy was requested in 65 patients (28.8% of all cases) and was completed in forty-six (20.4%). Molecular testing of CTNNB1 testing was requested in 35 cases (15.5%). APC germline test was requested in 12 cases. Four patients in our cohort had an FAP-associated DF.

CONCLUSIONS

CTNNB1 ± APC testing and colonoscopy are useful tools for the screening of patients with DF. CTNNB1 molecular testing should be performed in all cases of newly diagnosed DF. Negative CTNNB1 results, alongside clinical assessment, should prompt APC testing and/or colonoscopy.

Novel Pathogenic Germline Variant of the Adenomatous Polyposis Coli (APC) Gene, p.S2627Gfs*12 Identified in a Mild Phenotype of APC-Associated Polyposis: A Case Report

Patient: Male, 80-year-old

Final Diagnosis: Attenuated APC-associated polyposis

Symptoms: Colon polyps • renal carcinoma

Medication: —

Clinical Procedure: —

Specialty: Genetics

Mosaicism in Patients With Colorectal Cancer or Polyposis Syndromes: A Systematic Review

BACKGROUND & AIMS

Somatic mosaicism, in which variants arise post-zygotically and are therefore not present in all cells in the body, may be an underestimated cause of colorectal cancer (CRC) and polyposis syndromes. We performed a systematic review to provide a comprehensive overview of somatic mosaicism in patients with CRC and polyposis syndromes.

METHODS

We searched PubMed through March 2018 to identify reports of mosaicism in patients with CRC or polyposis syndromes. We divided the final set of studies into 3 subgroups describing APC mosaicism, mosaicism in other CRC susceptibility genes, and epigenetic mosaicism.

RESULTS

Of the 232 articles identified in our systematic search, 46 met the criteria for further analysis. Of these, 35 studies described mosaic variants or epimutations in patients with CRC or polyposis syndromes. Nineteen studies described APC mosaicism, comprising a total of 57 patients. Six described mosaicism in genes associated with familial CRC syndromes, such as Lynch and Cowden syndromes. Ten studies described epigenetic mosaicism, sometimes resulting from a germline variant (such as deletion of EPCAM).

CONCLUSIONS

We found that somatic mosaicism is underdiagnosed but critical for determining the clinical management of patients with de novo polyposis who possibly carry mosaic APC variants, and present a decision tree for the clinical management of these patients. Mosaicism in genes associated with susceptibility to CRC contributes to development of other familial CRC syndromes. Heritable epigenetic mosaicism is likely underestimated and could have a dominant pattern of inheritance. However, the inheritance of primary mosaic epimutations, without an underlying genetic cause, is complex and not fully understood.

Next-generation sequencing identifies 2 genomically distinct groups among pyloric gland adenomas

The molecular alterations identified among pyloric gland adenomas (PGAs) in the published literature are based on polymerase chain reaction of targeted genes, and next-generation sequencing (NGS) has not been performed. In this study, we performed NGS and correlated the molecular alterations with the histologic grade of dysplasia and immunohistochemical findings in a cohort of PGAs. Successful DNA extraction and sequencing were performed in 15 pyloric gland adenomas/adenocarcinoma from 12 patients. Additionally, 4 specimens of autoimmune gastritis were selected to serve as the control group. Ten PGAs with low-grade dysplasia were seen to have mutations in the triad of APC, KRAS, and GNAS genes. Five PGAs with high-grade dysplasia/adenocarcinoma exhibited mutations in several genes including APC, CTNNB1, KRAS, GNAS, TP53, CDKN2A, PIK3CA, and EPHA5 genes but did not exhibit mutations in the triad of APC, KRAS, and GNAS genes. The median tumor mutational burden was higher in PGAs with high-grade dysplasia/adenocarcinoma when compared with PGAs with low-grade dysplasia (5.25 and 4.38, respectively). PGAs with high-grade dysplasia/adenocarcinoma had more chromosomal gains and losses than PGAs with low-grade dysplasia. The molecular findings suggest that there are 2 separate mutator pathways of dysplasia development in PGAs.

The genetic basis of colonic adenomatous polyposis syndromes

Colorectal cancer (CRC) is one of the most common forms of cancer worldwide and familial adenomatous polyposis (FAP) accounts for approximately 1% of all CRCs. Adenomatous polyposis syndromes can be divided into; familial adenomatous polyposis (FAP) – classic FAP and attenuated familial adenomatous polyposis (AFAP), MUTYH-associated polyposis (MAP), NTHL1-associated polyposis (NAP) and polymerase proofreading-associated polyposis (PPAP). The polyposis syndromes genetics and clinical manifestation of disease varies and cases with clinical diagnosis of FAP might molecularly show a different diagnosis.

This review examines different aspects of the adenomatous polyposis syndromes genetics and clinical manifestation of disease; in addition the genotype-phenotype and modifier alleles of FAP will be discussed. New technology has made it possible to diagnose some of the APC mutation negative patients into their respective syndromes. There still remain many molecularly undiagnosed adenomatous polyposis patients indicating that there remain causative genes to be discovered and with today’s technology these are expected to be identified in the near future. The knowledge about the role of modifier alleles in FAP will contribute to improved pre-symptomatic diagnosis and treatment.

New novel mutations will continually be discovered in genes already associated with disease and new genes will be discovered that are associated with adenomatous polyposis. The search for modifier alleles in FAP should be made a priority.

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.

Association between the age and the development of colorectal cancer in patients with familial adenomatous polyposis: a multi-institutional study

PURPOSE

To investigate the incidence of colorectal cancer among familial adenomatous polyposis (FAP) patients by phenotype using the latest modalities.

METHODS

We collected data on 303 patients who underwent surgery for FAP at one of 23 institutions between 2000 and 2012. The incidence of colorectal cancer was investigated by phenotype.

RESULTS

Colorectal cancer was diagnosed in 115 (38.0 %) of the 303 patients. Overall, colorectal cancer with the attenuated, sparse, and profuse phenotypes was diagnosed at 30, 31, and 28 years of age, respectively, in 10 % of the patients and at 59, 48, and 41 years of age, respectively, in 50 % of the patients (P = 0.013). The patients with colorectal cancer were older than those without colorectal cancer for all phenotypes. The optimal cut-off age for predicting the development of colorectal cancer in the attenuated, sparse, and profuse phenotypes was 46, 31, and 27 years, respectively.

CONCLUSIONS

Patients with profuse and sparse phenotypes should undergo prophylactic proctocolectomy before their mid-to-late 20 s. On the other hand, the timing and type of surgery for patients with attenuated FAP (AFAP) should be decided individually with reference to the colonoscopic findings.

Two different nucleotide substitutions of APC gene in a family with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome leading to colorectal cancer. This disease appears as a result of germline mutation in adenomatous polyposis coli (APC) gene. The aim of the present study is to report the association between two different nucleotide substitutions detected in a family with FAP. In the proband, p.His1172Gln (c.3516delT) was detected in exon 15 of the APC gene. Furthermore, p.His1172Gln (c.3516delT) and, in addition to this mutation, p.Met1413Val (c.4237 A > G) were detected in exon 15 in both daughters of the proband. However, we believe that single nucleotide change in codon 1413 may be a polymorphic variant and deletion T in codon 1172 of APC gene is associated with FAP, attenuated FAP and extracolonic FAP involvement. Along with common use of genetic tests in the clinical practice, genotype–phenotype correlation may be recognized better and useful for early diagnosis and prevention of familial cancer syndromes.

Attenuated familial adenomatous polyposis with desmoids caused by an APC mutation

We present here a case of attenuated familial adenomatous polyposis (AFAP) with a family history of desmoids and thyroid tumors. This patient had no colonic polyps but did have multiple desmoids. Genetic analysis identified a 4-bp deletion in codon 2644 (c.7932_7935delTTAT: p.Tyr2645LysfsX14) of the adenomatous polyposis coli (APC) gene. In cases with limited numbers of colonic polyps and desmoids, AFAP may be caused by a mutation in the 3′ region of APC.

Diagnosis, surveillance, and treatment strategies for familial adenomatous polyposis: rationale and update

Familial adenomatous polyposis is characterized by the development of multiple (>100) colorectal adenomas throughout the colorectum. This disorder can be caused by a germline mutation in the adenomatous polyposis coli gene and can be diagnosed either clinically or genetically. After diagnosis with the condition, patients should undergo prophylactic proctocolectomy with a neoreservoir, usually an ileoanal pouch, at an appropriate time. Individuals with a family history of this disease who have not been diagnosed should be advised to attend genetic counseling and to enroll in appropriate clinical and genetic surveillance programs. Recent progress in endoscopic technology, including high-resolution endoscopy, capsule endoscopy, and double-balloon endoscopy, has made possible more detailed and wide-ranging investigation of the gastrointestinal tract. Although there has been limited evidence, further studies on these new endoscopic technologies might alter the surveillance strategies for familial adenomatous polyposis.

Sphingolipids in colon cancer

Colorectal cancer is one of the major causes of death in the western world. Despite increasing knowledge of the molecular signaling pathways implicated in colon cancer, therapeutic outcomes are still only moderately successful. Sphingolipids, a family of N-acyl linked lipids, have not only structural functions but are also implicated in important biological functions. Ceramide, sphingosine and sphingosine-1-phosphate are the most important bioactive lipids, and they regulate several key cellular functions. Accumulating evidence suggests that many cancers present alterations in sphingolipids and their metabolizing enzymes. The aim of this review is to discuss the emerging roles of sphingolipids, both endogenous and dietary, in colon cancer and the interaction of sphingolipids with WNT/β-catenin pathway, one of the most important signaling cascades that regulate development and homeostasis in intestine. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Identification of patients at risk for hereditary colorectal cancer

Diagnosis of hereditary colorectal cancer syndromes requires clinical suspicion and knowledge of such syndromes. Lynch syndrome is the most common cause of hereditary colorectal cancer. Other less common causes include familial adenomatous polyposis (FAP), Peutz-Jeghers syndrome (PJS), juvenile polyposis syndrome, and others. There have been a growing number of clinical and molecular tools used to screen and test at risk individuals. Screening tools include diagnostic clinical criteria, family history, genetic prediction models, and tumor testing. Patients who are high risk based on screening should be referred for genetic testing.

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.

Prevalence of skin lesions in familial adenomatous polyposis: a marker for presymptomatic diagnosis?

BACKGROUND AND AIMS

Benign skin tumors such as lipomas, fibromas, and epidermal cysts are among the extracolonic manifestations of familial adenomatous polyposis (FAP). Readily detectable by inspection, they could serve as presymptomatic diagnostic markers to identify FAP patients. We therefore prospectively determined the prevalence of cutaneous lesions in genetically confirmed adenomatous polyposis coli (APC) mutation carriers and assessed their potential usefulness in the identification of FAP patients.

METHODS

Whole-skin examination was performed in 56 adult APC mutation carriers, compared with a control group (n = 116). In addition, FAP patients were investigated for the presence of congenital hypertrophy of the retinal pigment epithelium (CHRPE), an established clinical marker for FAP, and a detailed review of medical records was performed.

RESULTS

Nearly half of all FAP patients (48.2%) had at least one FAP-associated skin lesion, compared with one third (34.5%) of controls. Only multiple lipomas and combined skin lesions were significantly more prevalent in APC mutation carriers. CHRPE was observed in 22 (43.1%) of 51 FAP patients, including 14 (37.8%) of 37 individuals with APC mutations outside the CHRPE-associated region between codons 311 and 1465.

CONCLUSIONS

Despite a significantly higher prevalence of multiple lipomas, occurring at younger age, and combined skin lesions in APC mutation carriers, the low diagnostic sensitivity of FAP-associated skin lesions precludes their use as markers for FAP in clinical practice. Based on our findings, the common CHRPE-associated region should be extended to APC codons 148-2043.

Genotype-phenotype correlation in colorectal polyposis

Familial adenomatous polyposis (FAP) has been divided into three clinical subtypes: mild, classical and severe. This study aimed to investigate for a correlation between genotype and phenotype. A codon-specific survival difference is unknown. A retrospective longitudinal study of 492 patients on the Manchester Polyposis Registry was conducted. Patients were grouped according to genotypes: 0, unknown mutation; 1, adenomatous polyposis coli (APC) 0-178 (and 312-412 of exon 9); 2, APC >1550; 3, APC 179-1249; 4, APC 1250-1549; and 5, MutYH. Date of onset of polyposis, incidence of colorectal cancer (CRC), survival and actuarial time to surgery were calculated. Median age of onset of polyposis for genotype 0 was 20.3 years, genotype 1 35.6 years, genotype 2 32.2, genotype 3 15.9 years, and genotype 4 14.8 years (p < 0.0001). Age of onset of CRC was similar between genotypes. Median survival for genotype 0 was 56.6 years, genotype 1 74.9 years, genotype 2 61.0 years, genotype 3 63.0 years, genotype 4 48.1 years, and genotype 5 69.7 years (p = 0.003). This survival difference was also seen when patients who underwent screening and those who did not were analysed separately. Survival in the screened population was 53.9 years in genotype 4 and 72.9 years in genotype 3. Patients with genotype 4 (APC 1249-1549) have a significantly worse survival despite screening and early prophylactic surgery. This analysis supports a genotype-phenotype correlation. Patients with a mutation APC 1249-1549 develop polyposis at an early age and have a worse survival. Patients with a mutation APC 0-178 or 312-412 develop polyposis later and have an improved survival. This survival difference has not previously been documented.

Lower gastrointestinal tract cancer predisposition syndromes

Although inherited predisposition to colorectal cancer (CRC) has been suspected for more than 100 years, definitive proof of Mendelian syndromes had to await maturation of molecular genetic technologies. Since the l980s, the genetics of several clinically distinct entities has been revealed. Five disorders that share a hereditary predisposition to CRC are reviewed in this article.

Genotype to phenotype: analyzing the effects of inherited mutations in colorectal cancer families

With improvements to DNA sequencing technologies, including the advent of massively parallel sequencing to perform "deep sequencing" of tissue samples, the ability to determine all of the nucleotide variations in a tumor becomes a possibility. This information will allow us to more fully understand the heterogeneity within each tumor, as well as to identify novel genes involved in cancer development. However, the new challenge that arises will be to interpret the pathogenic significance of each genetic variant. The enormity and complexity of this challenge can be demonstrated by focusing on just the genes involved in the hereditary colon cancer syndromes, familial adenomatous polyposis (FAP) and hereditary non-polyposis coli (HNPCC). The genes responsible for each disease were identified almost two decades ago -APC for FAP and the MMR genes for HNPCC - and a large number of germline variations have been identified in these genes in hereditary cancer patients. However, relating the effect of an individual genotype to phenotype is not always straightforward. This review focuses on the roles of the APC and MMR genes in tumor development and the work that has been done to relate different variants in each gene to functional aberrations and ultimately tumorigenesis. By considering the work that has already been done on two well-defined diseases with clear genetic associations, one can begin to understand the challenges that lie ahead as new genes and gene mutations are discovered through tumor sequencing.

[Colorectal cancer in familial adenomatous polyposis: Are there clinical predictive factors?]

BACKGROUND

Familial Adenomatous Polyposis (FAP) is a hereditary disorder with multiple colorectal polyps that exhibit an almost inevitable risk of colorectal cancer (CRC) in untreated patients.

GOALS

To evaluate clinical features related to CRC risk at diagnosis.

MATERIAL AND METHODS

Charts from 88 patients were reviewed to collect information regarding age, family history, symptoms, polyposis severity and association with CRC.

RESULTS

41 men (46.6%) and 47 women (53.4%) were assisted. CRC was detected in 53 patients (60.2%), with a frequency of 9.1% under 20 years, 58% between 21-40 and 85% over 41 years of age. Average age of patients without CRC was lower at treatment (29.5 vs. 40.0 years; p=0.001). Family history was reported by 58 patients (65.9%), whose average age did not differ from those who didn't report it (33.4 vs. 34.4; p=0.17). Asymptomatic patients comprised 10.2% of the total; in this group, CRC incidence was much lower when compared to those presenting symptoms (1.1% vs. 65.8%; p=0.001). Patients without CRC presented a shorter length of symptoms (15.2 vs. 26.4 months; p=0.03) and less frequent weight loss (11.4% vs. 33.9%; p=0.01). At colonoscopy, polyposis was classified as attenuated in 12 patients (14.3%), who presented greater average age (48.2 vs. 33.3 years; p=0.02) and equal CRC incidence (58.3% vs. 58.3%; p=0.6) when compared to those with classic polyposis.

CONCLUSIONS

The risk of CRC in FAP patients 1) increases significantly after the second decade; 2) is associated with higher age, weight loss, presence and duration of simptomatology; 3) is similar in patients with attenuated or classic phenotype.

Clinical and genetic characterization of classical forms of familial adenomatous polyposis: a Spanish population study

BACKGROUND

Classical familial adenomatous polyposis (FAP) is characterized by the appearance of >100 colorectal adenomas.

PATIENTS AND METHODS

We screened the APC and MUTYH genes for mutations and evaluated the genotype-phenotype correlation in 136 Spanish classical FAP families.

RESULTS

APC/MUTYH mutations were detected in 107 families. Sixty-four distinct APC point mutations were detected in 95 families of which all were truncating mutations. A significant proportion (39.6%) had not been previously reported. Mutations were spread over the entire coding region and great rearrangements were identified in six families. Another six families exhibited biallelic MUTYH mutations. No APC or MUTYH mutations were detected in 29 families. These APC/MUTYH-negative families showed clinical differences with the APC-positive families. A poor correlation between phenotype and mutation site was observed.

CONCLUSIONS

Our results highlight that a broad approach in the genetic study must be considered for classical FAP due to involvement of both APC and MUTYH and the heterogeneous spectrum of APC mutations observed in this Spanish population. The scarcely consistent genotype-phenotype correlation does not allow making specific recommendations regarding screening and management. Differences observed in APC/MUTYH-negative families may reflect a genetic basis other than mutations in APC and MUTYH genes for FAP predisposition.

Role of surgery in familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer (Lynch syndrome)

Surgery remains the mainstay of treatment for patients who develop colorectal cancer (CRC) in the setting of a hereditary CRC syndrome. In patients with a hereditary CRC syndrome, surgery can be prophylactic, therapeutic with curative intent, and, in some cases, palliative. The type and extent of surgical resection in familial adenomatous polyposis (FAP) and in the Lynch syndrome is influenced by differences in the natural history of carcinogenesis between the two syndromes and by the effectiveness of and patient compliance with available surveillance strategies. In this article, the surgical options for the management of patients with FAP and Lynch syndrome are discussed.

Genetic counselling for cancer and risk perception

The main aim was to investigate risk perception and psychological distress in individuals attending genetic counselling. A consecutive series of 86 individuals with a diagnosis and/or family history of breast, ovarian or colorectal cancer was included. Risk assessments were performed before and immediately after genetic counselling and at a one-year follow-up. Psychological distress was assessed 1 week before, and 6 weeks, 6 months and 1 year after genetic counselling. The number of individuals who correctly-estimated the general risk in the population increased significantly from 35%, before to 82% after counselling (p < 0.001). One year later, data on general risk estimates showed a significant reduction of the number of correct estimations to 51%, compared with directly after the counselling (p < 0.005). In total, 54% estimated their own lifetime risk correctly after the counselling, compared with 17% before (p < 0.001) (those with a cancer diagnosis estimated the risk of their children developing cancer). One year later, the number of correct estimations had dropped to 28%. Before the counselling, the majority of the participants overestimated both the general risk and their own/children's risk. The participants experienced moderate levels of psychological distress before the counselling and a decrease of anxiety afterwards (p < 0.02). However, half of the participants reported moderate or high distress. There were no differences in psychological distress between those who estimated their risk/ children's risk as low, moderate or high or between those who over-, under- or correctly estimated their own/children's risk. Further investigations are needed to develop and adjust the risk information provided to the individual in order to avoid misunderstanding, especially as this information is going to be revealed to family members Counselling support should be offered to those individuals who experience psychological distress.

Hereditary colorectal cancer syndromes and the role of the surgical oncologist

The expanding understanding of the genetic basis to hereditary colon cancer syndromes is dismantling previously conceived categorizations and shedding light on why those schemes often failed in past. This review highlights evolving concepts regarding the genetic diagnosis and clinical management of the more commonly inherited colorectal cancer syndromes, including a discussion of recently described familial syndromes. This review also addresses clinician responsibilities in recognition of familial syndromes and provision of counseling.

[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.

Hereditary colorectal cancer syndromes: familial adenomatous polyposis and lynch syndrome

Familial colorectal cancer (CRC) accounts for 10% to 20% of all cases of CRC. Two major autosomal dominant forms of heritable CRC are familial adenomatous polyposis (FAP) and Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer). Along with the risk for CRC, both syndromes are associated with elevated risk for other tumors. Improved understanding of the genetic basis of these diseases has not only facilitated the identification and screening of at-risk individuals and the development of prophylactic or early-stage intervention strategies but also provided better insight into sporadic CRC. This article reviews the clinical and genetic characteristics of FAP and Lynch syndrome, recommended screening and surveillance practices, and appropriate surgical and nonsurgical interventions.

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.

Genetic alteration in hereditary colorectal cancer

Colorectal cancer is a major cause of morbidity and mortality. Both genetic and environmental factors contribute to cancer aetiology. About 15-20% of all colorectal cancers are familial. Approximately 6% of colorectal cancers can be attributed to recognizable heritable germline mutations. The discovery of genes responsible for inherited forms of colorectal cancer have the potential to improve cancer risk assessment and counselling. Genetic testing for hereditary forms of colorectal cancer can confirm or reject diagnoses at the molecular level, determine surveillance intervals for at-risk persons, decrease the cost of surveillance by risk stratification, aid in surgical and chemoprevention decision-making, and help patients in family and career planning. This paper reviews the genetics behind genes and molecular study of the hereditary colorectal cancer. This may help the medical professionals especially internists, gastroenterologists, and oncologists to update their knowledge in this field.

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.

The patient with multiple intestinal polyps

The management of patients with multiple intestinal polyps may be difficult and greatly depends on the correct classification. Polyposis syndromes account for less than 1% of newly diagnosed colorectal cancers. In addition the risk for extracolonic cancer is increased in most syndromes. Here we report the case of a difficult patient with severe gastric polyposis and we present a review of polyposis syndromes such as classical and attenuated familial adenomatous polyposis (FAP), MYH-associated polyposis, Peutz-Jeghers syndrome, juvenile polyposis as well as rare polyposis syndromes. The most practical approach for the diagnostic workup in patients with newly diagnosed gastrointestinal polyposis is based on the histological typing of polyps. In addition, a detailed family history regarding cancer, polyps and congenital abnormalities should be obtained from every polyposis patient. Patients with multiple adenomas are most likely to suffer from FAP, AFAP or MAP. Of these, younger age and higher polyp count are most likely a diagnosis of typical FAP. Older age and fewer polyps favour a diagnosis of AFAP or MAP. Germline testing of the APC gene is suggested, and if negative, MYH gene testing should be done. In patients with hamartomas, extraintestinal features should be evaluated and reference histology should be initiated. In addition panintestinal imaging should be performed with EGD, colonoscopy and small bowel imaging (PE, CE, and MR) enteroclysis. For diagnostic and therapeutic problems a familial colorectal cancer center should be consulted. Using this algorithm, correct classification and adequate treatment should be possible for every polyposis patient.

Correlations between mutation site in APC and phenotype of familial adenomatous polyposis (FAP): A review of the literature

Mutations in the adenomatous polyposis coli (APC) gene cause familial adenomatous polyposis (FAP). Disease severity and the presence of extracolonic manifestations seem to be correlated with the location of the mutation on the APC gene. In this review, large studies describing genotype-phenotype correlations in FAP were evaluated and categorized. Attenuated FAP (AFAP, <100 colorectal adenomas) is correlated with mutations before codon 157, after codon 1595 and in the alternatively spliced region of exon 9. Severe polyposis (>1000 adenomas) is found in patients with mutations between codons 1250 and 1464. Mutations in the remainder of the APC gene cause an intermediate phenotype (hundred to thousands of adenomas). Congenital hypertrophy of the retinal pigment epithelium (CHRPE) and desmoid tumours are associated with mutations between codons 311 and 1444 and after codon 1444, respectively. No consistent correlations were found for upper gastrointestinal tumours. Genotype-phenotype correlations in FAP will be useful in decisions concerning screening and surgical management of FAP.

Screening for colon cancer

Colorectal cancer screening reduces mortality in individuals 50 years and older. Each of the screening tests currently available has advantages and limitations, and there is no consensus as to which test or combination of tests is best. What is clear, however, is that the rates of colorectal cancer screening remain low. This review summarizes the clinical evidence supporting colorectal cancer screening in the average risk population and in high risk groups, discusses the advantages and disadvantages of the available screening tests, outlines the currently recommended guidelines for screening based on risk category, and discusses new and emerging technologies for colorectal cancer screening.

Surveillance and management of upper gastrointestinal disease in Familial Adenomatous Polyposis

Almost all patients affected by Familial Adenomatous polyposis (FAP) will develop foregut as well as hindgut polyps, and following prophylactic colectomy duodenal cancer constitutes one of the leading causes of death in screened populations. Without prophylactic colectomy, FAP patients predictably develop colorectal cancer, but the lifetime risk of upper gastrointestinal cancer is lower, estimated at approximately 5%. Management of the upper gastrointestinal cancer risk is one of the greatest challenges facing clinicians involved in the care of Polyposis families, and with improved survival following prophylactic colectomy, the burden of foregut disease (particularly duodenal adenomatosis) will increase. Until recently, the value of upper gastrointestinal surveillance in FAP populations has been contentious, but with improved understanding of the natural history coupled with developments in surgery, interventional endoscopy and medical therapy, treatment algorithms for duodenal adenomatosis in FAP are becoming clearer.

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.

Molecular pathogenesis of colorectal cancer: implications for molecular diagnosis

Colorectal cancer is the third leading cause of cancer-related death in both men and woman in industrialized countries. Major advances have been made in our understanding of molecular events leading to formation of adenomatous polyps and cancer. Most colorectal cancers are sporadic, but a significant proportion (5-6%) has a clear genetic background. It is now widely accepted that colorectal carcinogenesis is a multistep process involving the inactivation of a variety of tumor-suppressor and DNA-repair genes and simultaneous activation of certain oncogenes. In addition, epigenetic alterations through aberrant promoter methylation and histone modification have been found to play a major role in the evolution and progression of a large proportion of sporadic colon cancers. Consequently, it is now apparent that individual colorectal cancers may evolve through diverse molecular pathways. In this article, the authors have summarized the current knowledge of molecular pathogenesis in common hereditary syndromes and sporadic forms of colorectal cancer. Novel molecular diagnostic tools for the early diagnosis and prevention of colorectal cancer that have emerged from these insights are discussed.

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.

Inherited susceptibility to colorectal cancer

The principal Mendelian disorders predisposing to colorectal cancer are familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). FAP is due to mutations in the APC gene. HNPCC is due to a mutation in one of at least five mismatch repair genes. Identification of individuals with these conditions is important because colon cancer will occur in approximately 80% and onset is early. For FAP, protein truncation testing will identify the vast majority of mutations. For HNPCC, 80%-95% can be identified by microsatellite instability testing. A current U.S. study reports that 12% of consecutive colorectal cancers have high microsatellite instability and that, of this 12%, 25% have detectable mutations of MLH1, MSH2, or MSH6. Potential benefits of identification include improved compliance with recommended surveillance, early detection of polyps, reduction in cancer mortality, offering of testing to relatives, and reassurance for relatives found to be negative with attendant savings in the time and expense of surveillance.

Genetic testing for germline mutations of the APC gene in patients with apparently sporadic desmoid tumors but a family history of colorectal carcinoma

PURPOSE

Desmoid tumors, also known as aggressive fibromatosis, occur with an incidence of 10 to 15 percent in patients affected by familial adenomatous polyposis, an autosomal inherited disease caused by germline mutations in the APC gene. However, sporadic forms with no hereditary background exist. The aim of this study was to find out whether there are APC germline mutations in apparently sporadic desmoid tumor patients without clinical or familial signs of familial adenomatous polyposis but with a family history of colorectal carcinoma in at least one family member.

METHODS

Genomic DNA and mRNA were isolated from peripheral blood leukocytes of index patients of eight nonrelated families. Mutation screening was performed using reverse transcriptase polymerase chain reaction-based protein truncation test for APC exons 1-14. The large APC exon 15 was scrutinized by the protein truncation test of four overlapping genomic fragments. Additionally, genomic DNA from five desmoid tumors was analyzed for loss of heterozygosity at D5S346 close to the APC locus.

RESULTS

No translational stop mutations typical for familial adenomatous polyposis could be found in the APC gene in any of the analyzed blood samples from the desmoid tumor patients. Additionally, no loss of heterozygosity at D5S346 was found in four of five desmoids; one tumor was not informative.

CONCLUSIONS

These results may suggest that patients with sporadic desmoids and no clinical signs of familial adenomatous polyposis detected on careful examination, esophagogastroduodenoscopy, and complete colonoscopy do not need to be tested routinely for germline mutations of the APC gene. However, as large studies dealing with this problem are absent, it might be more time and cost effective to perform an APC mutational analysis instead.

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.

Exclusion of an extracolonic disease modifier locus on chromosome 1p33–36 in a large Swiss familial adenomatous polyposis kindred

Familial adenomatous polyposis (FAP), an autosomal dominantly inherited colorectal cancer predisposition syndrome, displays considerable inter- and intrafamilial phenotypic heterogeneity, which represents a major problem in genetic counselling of APC mutation carriers. The Min mouse model indicated a putative disease modifier locus on chromosome 4, which is syntenic to human chromosome 1p35-36. This finding was subsequently supported by parametric and nonparametric linkage analyses in FAP families, however, without identifying functional variants in candidate genes. Recently, germline mutations in the base-excision repair gene MYH (1p33-34) have been described in patients with multiple adenomas, pointing to a possible role as disease modifier in FAP. Here, we present critical reassessment of one of the largest FAP kindreds published, which was previously used in linkage mapping of 1p35-36. In this family, all affected members harbour the same APC germline mutation (5945delA), but display marked phenotypic variability, in particular regarding the occurrence of extracolonic disease that segregates in several branches of the family tree. Using updated clinical information, additional mutation carriers and polymorphic markers, fine mapping of the critical region as well as mutation analysis of the MYH gene were performed. These investigations allowed us to significantly exclude (i) the 1p33-36 region as a modifier locus and (ii) MYH as a modifier gene for extracolonic disease in this FAP kindred. Our results do not eliminate 1p33-36 from suspicion in other families, but clearly indicate that in our family linkage analysis of further putative candidate regions is necessary to identify a disease modifier locus in FAP.