Whole-gene APC deletions cause classical familial adenomatous polyposis, but not attenuated polyposis or "multiple" colorectal adenomas

Familial adenomatous polyposis (FAP) is a dominantly inherited colorectal tumor predisposition that results from germ-line mutations in the APC gene (chromosome 5q21). FAP shows substantial phenotypic variability: classical polyposis patients develop more than 100 colorectal adenomas, whereas those with attenuated polyposis (AAPC) have fewer than 100 adenomas. A further group of individuals, so-called "multiple" adenoma patients, have a phenotype like AAPC, with 3-99 polyps throughout the colorectum, but mostly have no demonstrable germ-line APC mutation. Routine mutation detection techniques fail to detect a pathogenic APC germ-line mutation in approximately 30% of patients with classical polyposis and 90% of those with AAPC/multiple adenomas. We have developed a real-time quantitative multiplex PCR assay to detect APC exon 14 deletions. When this technique was applied to a set of 60 classical polyposis and 143 AAPC/multiple adenoma patients with no apparent APC germ-line mutation, deletions were found exclusively in individuals with classical polyposis (7 of 60, 12%). Fine-mapping of the region suggested that the majority (6 of 7) of these deletions encompassed the entire APC locus, confirming that haploinsufficiency can result in a classical polyposis phenotype. Screening for germ-line deletions in APC mutation-negative individuals with classical polyposis seems warranted.     

APC gene mutations and extraintestinal phenotype of familial adenomatous polyposis.

BACKGROUND: Familial adenomatous polyposis (FAP) is caused by germline mutation of the adenomatous polyposis coli (APC) gene on chromosome 5q. AIMS: This study assessed genotype-phenotype correlations for extraintestinal lesions in FAP. METHODS: Mutations of the APC gene were compared with the occurrence of seven extraintestinal manifestations in 475 FAP patients from 51 families. The frequency of manifestations was adjusted for different ages of patients using person years of exposure. In pedigrees without identified APC gene mutation, analysis of linkage to chromosome 5q and/or assessment of neoplasms for replication errors characteristic of mutation in mismatch repair genes were performed. RESULTS: FAP patients from the 42 families (82%) with identified mutations of the APC gene had more frequent expression of extraintestinal manifestations than affected individuals without identified mutations (risk ratio 1.2-4.0; significant difference for cutaneous cysts). The presence of a cutaneous cyst or extraintestinal cancer significantly increased the likelihood of detection of a mutation in the APC gene (94% and 92% respectively; p < 0.05). In patients without identified APC gene mutation, linkage to the APC gene was found in one large family (lod = 5.1, theta 0.01), and replication error phenotype was absent in all 24 neoplasms from 16 members of these nine pedigrees. Expression of pigmented ocular fundus lesions was strongly associated with mutations in codons 541-1309, but no other extraintestinal manifestations were related to mutation position. Multiplicity of extraintestinal manifestations was high with mutation in codons 1465, 1546, and 2621. CONCLUSIONS: Patients with the colorectal phenotype of FAP but no extraintestinal manifestations may have non-truncating mutations of the APC gene or mutation in a gene other than APC or mismatch repair genes. The site of APC gene mutation is associated with pigmented ocular fundus lesions (codons 542-1309) and predisposition to multiplicity of extraintestinal manifestations (codons 1465, 1546, and 2621).     

APC gene mutations in Chinese familial adenomatous polyposis patients

AIM:To study the characteristics of APC(adenomatous polyposis coli)gene germline mutation in Chinese patients with familial adenomatous polyposis(FAP).METHODS:APC gene from 14 FAP families was amplified by polymerase chain reaction(PCR)and underwent direct sequencing to determine the micromutation type.For the samples without micromutation,the large fragment deletion of APC gene was examined by multiplex ligation-dependent probe amplification(MLPA).RESULTS:There were gene micromutations in 9 families with a...     

Familial adenomatous polyposis patients without an identified APC germline mutation have a severe phenotype

BACKGROUND: Development of more than 100 colorectal adenomas is diagnostic of the dominantly inherited autosomal disease familial adenomatous polyposis (FAP). Germline mutations can be identified in the adenomatous polyposis coli (APC) gene in approximately 80% of patients. The APC protein comprises several regions and domains for interaction with other proteins, and specific clinical manifestations are associated with the mutation assignment to one of these regions or domains. AIMS: The phenotype in patients without an identified causative APC mutation was compared with the phenotype in patients with a known APC mutation and with the phenotypes characteristic of patients with mutations in specific APC regions and domains. PATIENTS: Data on 121 FAP probands and 149 call up patients from 70 different families were extracted from the Danish Polyposis register. METHODS: Differences in 16 clinical manifestations were analysed according to the patient's mutational status. Two sided independent t sample test, two sided chi(2) test, and odds ratios were calculated. RESULTS: Patients without identified APC mutations had a unique and severe phenotype, which was roughly described as: young age at diagnosis and subsequent death in spite of development of few colorectal adenomas; low risk of involvement of the upper gastrointestinal tract, as reflected by a low mean Spigelman stage, and a low risk of fundic gland polyposis. Finally, they had significantly fewer affected family members, although they do not themselves more often represent an isolated case. CONCLUSIONS: The severe phenotype should be considered when counselling FAP families in which attenuated FAP is excluded and in which a causative APC mutation has not been identified.     

Analysis of masked mutations in familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal-dominant disease characterized by the development of hundreds of adenomatous polyps of the colorectum. Approximately 80% of FAP patients can be shown to have truncating mutations of the APC gene. To determine the cause of FAP in the other 20% of patients, MAMA (monoallelic mutation analysis) was used to independently examine the status of each of the two APC alleles. Seven of nine patients analyzed were found to have significantly reduced expression from one of their two alleles whereas two patients were found to have full-length expression from both alleles. We conclude that more than 95% of patients with FAP have inactivating mutations in APC and that a combination of MAMA and standard genetic tests will identify APC abnormalities in the vast majority of such patients. That no APC expression from the mutant allele is found in some FAP patients argues strongly against the requirement for dominant negative effects of APC mutations. The results also suggest that there may be at least one additional gene, besides APC, that can give rise to FAP.     

An unexpected Cowden syndrome case found among members of a large familial adenomatous polyposis kindred

Genetic testing is now considered the standard of care in the management of familial adenomatous polyposis (FAP). Non-carriers of mutations are excluded from endoscopic surveillance. During the systematic screening of the relatives of an affected member with FAP, one non-carrier of APC mutations was unexpectedly found with the typical Cowden syndrome phenotype. One large Algerian family with FAP was screened for an APC germline mutation. Moreover, we also performed a mutation search in the Cowden syndrome member for PTEN, BMPR1A or MADH4 (SMAD4) germline mutations. We identified a mutation in the APC gene that results in a truncated protein (Y935X) in the FAP proband, and subsequently in 12 FAP-affected members. Among the 12 APC mutation-negative members of this family, we found one member with the Cowden disease phenotype. However, the mutation analysis in the PTEN gene and the two other genes involved in juvenile polyposis, namely BMPR1A and MADH4 (SMAD4), in the Cowden syndrome patient failed to show any pathogenic mutation. Genetic testing is a powerful tool that can provide a definitive diagnosis for FAP. However, not all polyposes in the FAP family are adenomatous polyposes.     

Desmoid tumours in familial adenomatous polyposis.

Desmoids are rare, benign fibromatous lesions, which can arise in patients with familial adenomatous polyposis (FAP), a disorder caused by germline adenomatous polyposis coli (APC) gene mutation. This study investigated the risk of desmoids in FAP, the relation between specific APC gene mutations and desmoid formation, and the clinical characteristics of FAP patients with desmoids. Eighty three of 825 FAP patients (10%) from 49 of 161 kindreds (30%) had desmoids. The absolute risk of desmoids in FAP patients was 2.56/1000 person years; comparative risk was 852 times the general population. APC gene mutations were similar in families with and without desmoids. The female/male ratio was 1.4 (p = NS). Previous abdominal surgery was noted in 68% of patients with abdominal desmoids (55% developed within five years postoperatively). Desmoid risk in FAP family members of a desmoid patient was 25% in first degree relatives v 8% in third degree relatives. Desmoids are a comparatively common complication of FAP associated with surgical trauma and familial aggregation. Desmoid development was not linked to specific APC gene mutations and was not found predominantly in women. Studies of chemopreventive therapy, given within five years after abdominal surgery, should be considered in FAP patients with a family history of desmoid disease.     

Phenotypic differences in familial adenomatous polyposis based on APC gene mutation status

Background—Familial adenomatous polyposis(FAP) is a clinically well defined hereditary disease caused bygermline mutations within the adenomatous polyposis coli (APC) gene.Although several techniques are applied in the mutation analysis of FAPkindreds about 20-50% of cases remain unclear, with no APC mutationidentified (APC negative).
Aims—To delineate phenotypic differences betweenAPC positive and APC negative patients with respect to colonic andextracolonic disease in order to determine whether additionalmechanisms are involved in the pathogenesis of FAP.
Methods—The entire coding region of the APC genewas analysed using single stranded conformation polymorphism andprotein truncation tests in 50 Swiss FAP families with a total of 161affected individuals. Differences in phenotypic manifestation werestatistically evaluated by Student's t test, Fisher'sexact test, and χ² test.
Results—Thirty six families (72%) were APCpositive. Statistically significant differences between APC positiveand APC negative groups were found for the mean age at diagnosis ofcolonic polyposis (35.2 versus 45.3 years, respectively) and for theoccurrence of stomach polyps (14 patients, all APC positive).Additionally, APC negative patients displayed lower polyp numbers atdiagnosis and less extracolonic manifestations.
Conclusions—FAP kindreds without detected APCgene mutations present with a notably milder disease phenotype comparedwith APC positive families, suggesting that different genetic factors might be involved.

Keywords:familial adenomatous polyposis; adenomatouspolyposis coli gene; mutation; colorectal cancer; extracolonicmanifestations

     

Genetic and clinical characterisation of familial adenomatous polyposis: a population based study

BACKGROUND: Familial adenomatous polyposis (FAP) is a rare autosomal dominantly inherited disease predisposing to colon cancer and caused by germline mutations in the APC (adenomatous polyposis coli) gene. AIMS: We conducted a population based study to evaluate the prevalence and clinical implications of APC mutations among Finnish FAP kindreds. A possible founder effect in parallel with previous observations in hereditary non-polyposis colon cancer (HNPCC) was addressed. PATIENTS: Affected individuals from 65 kindreds were included. METHODS: The APC gene was screened for mutations using the protein truncation test and heteroduplex analysis. Haplotype analysis was performed with four flanking microsatellite markers. Families that failed to show any mutations were scrutinised with Southern blot hybridisation and allelic expression analysis. RESULTS: Thirty eight different germline mutations in APC were identified in 47 kindreds (72%). The majority of these mutations were novel and unique to each family. Although sharing the classical polyposis phenotype, families without detectable APC mutations differed from mutation positive families in the following respects: firstly, mean age at polyposis diagnosis was higher (38.6 years (48 individuals) v 30.0 years (140 individuals); p=0.001); and secondly, the proportion of kindreds lacking extracolonic disease was higher (6/18 v. 5/47; p=0.04). CONCLUSIONS: Our results may pave the way for predictive testing in mutation positive families and should stimulate further molecular studies in mutation negative families. No founder effect was observed, which is in contrast with HNPCC in the same population.     

Preliminary results of the molecular diagnosis of familial adenomatous polyposis in Cuban families

BACKGROUND AND AIMS: Familial adenomatous polyposis (FAP) is an autosomal dominant condition characterized by multiple adenomatous polyps in the colon and rectum that inevitably develop into adenocarcinomas if the patient's colon is not removed in time. To date more than 500 mutations related to the disease have been identified in the APC (adenomatous polyposis coli) gene. The molecular study of FAP families was initially introduced in Cuba with the aim of identifying the asymptomatic carriers of APC gene mutations in each family. PATIENTS AND METHODS: We studied 23 individuals from 17 Cuban families who had been diagnosed clinically with FAP. Peripheral DNA was extracted from the index case of each family. Exon 15 of the APC gene was screened for germinal mutations using PCR and DNA heteroduplex. RESULTS: Three different germinal mutations were identified in the mutational clustering region of APC gene by sequencing analysis in five FAP unrelated families. Three families carry the most frequent mutation in APC in codon 1309, while the other two families carry mutations in codons 1061 and 1192, respectively. Two asymptomatic carriers of one family were detected, and later the disease was confirmed by colonoscopy in a very early stage while six members at risk were found to be negative. CONCLUSION: For the first time in Cuba molecular diagnosis of FAP was performed and the development of colorectal cancer prevented in asymptomatic carriers.     

五个家族性腺瘤性息肉病家系分析

目的分析5个家族性腺瘤性息肉病（FAP）家系,总结常染色体显性遗传规律。 方法对5个FAP家系进行调查分析,取外周血、粪便行全外显子组测序（WES）筛查大肠癌基因,行结肠镜检查并取活体组织进行病理分析。 结果5个家系中,连续几代发生FAP,当父亲或者母亲患FAP后,其子代发生FAP的概率均等（50%）,无性别差异,发病者均存在腺瘤样结肠息肉病基因（APC）突变,未成年人中未见发病,部分患者患有2种以上肿瘤。 结论在有FAP病史的家系中,未成年人一般不发病,成年后均需要进行APC基因检测及结肠镜检查,一旦发现腺瘤需要尽早进行内镜下治疗,避免结直肠癌的发生。     

Familial adenomatous polyposis: more evidence for disease diversity and genetic heterogeneity

Familial adenomatous polyposis (FAP) is characterised by the presence of profuse colonic carpeting of adenomas throughout the entire colon and rectum. The genetic basis of FAP has been shown to be primarily associated with germline mutations in the APC gene. Notwithstanding, several reports have been published indicating that there is genetic heterogeneity in FAP and that the most likely explanation is the existence of another gene. In this report we further delineate the genotype/phenotype correlation in families that harbour germline mutations in the APC gene and identify some previously unreported changes in the APC gene which predispose to an attenuated disease phenotype. From 53 index patients diagnosed with either FAP or attenuated FAP, 27 harboured changes in the APC gene. The remaining 26 patients were further subgrouped according to their colonic phenotype. There were nine patients with a mixed hyperplastic/adenomatous colonic phenotype and there were 17 patients with an adenomatous colonic phenotype. Evaluation of the disease characteristics of these patients and their families is presented which may aid in the identification of new genes associated with colonic polyposis.     

Hepatoblastoma and APC gene mutation in familial adenomatous polyposis.

BACKGROUND: Hepatoblastoma is a rare, rapidly progressive, usually fatal childhood malignancy, which if confined to the liver can be cured by radical surgical resection. An association between hepatoblastoma and familial adenomatous polyposis (FAP), which is due to germline mutation of the APC (adenomatous polyposis coli) gene, has been confirmed, but correlation with site of APC mutation has not been studied. AIM: To analyse the APC mutational spectrum in FAP families with hepatoblastoma as a possible basis to select kindreds for surveillance. PATIENTS: Eight patients with hepatoblastoma in seven FAP kindreds were compared with 97 families with identified APC gene mutation in a large Registry. METHODS: APC gene mutation was evaluated by RNase protection assay or in vitro synthesis protein assay. The chi 2 test and correlation were used for data analysis. RESULTS: APC gene mutation was identified in all seven FAP kindreds in which an at risk member developed hepatoblastoma. A male predominance was noted (six of eight), similar to literature cases (18 of 25, p < 0.01. Mutations were restricted to codons 141 to 1230, but no significant difference in site of mutation between pedigrees with and without hepatoblastoma was identified. CONCLUSIONS: Hepatoblastoma occurs primarily in boys in FAP kindreds and is associated with germline APC mutation in the 5' end of the gene. However, the site of APC mutation cannot be used to predict occurrence of this extracolonic cancer in FAP pedigrees.     

Multicenter experience with upper gastrointestinal polyps in pediatric patients with familial adenomatous polyposis

BACKGROUND: Familial adenomatous polyposis (FAP) is a hereditary cancer syndrome that includes gastro-duodenal involvement, polyposis, and a propensity to adenocarcinoma necessitating endoscopic surveillance. There are few data describing pediatric upper gastrointestinal FAP resulting in conflicting screening recommendations. OBJECTIVES: To characterize pediatric gastroduodenal FAP and to investigate the association between symptoms at endoscopy and APC mutation analysis with endoscopic-histologic findings warranting surveillance. METHOD: A retrospective chart review was performed, including all children with FAP who underwent upper endoscopy (EGD) at two institutions; (UNMC: 1992-2002, JHH: 1983-2002), all biopsies were reviewed and the APC mutations present in the cohort of patients were correlated to the pattern of severity of endoscopic findings and the frequency of APC mutations identified through commercially available testing for FAP (Labcorp: 1998-2002). RESULTS: Twenty-four patients from 21 families underwent 49 EGDs. Eighty-three percent were asymptomatic at the time of endoscopy. The most common finding was fundic gland polyposis (FGP) (51%), of which 42% and 15% harbored dysplasia and changes indefinite for dysplasia, respectively. Periampullary duodenal adenomata were present in 41% of patients with one patient necessitating ampullectomy. Symptoms at endoscopy were not predictive of premalignant changes. In 15 patients where the APC mutation was known patients with dysplastic FGP, gastric, or duodenal adenoma were more likely to harbor a mutation between codons 1225-1694 than the reference population (p= 0.006). CONCLUSIONS: All pediatric patients with FAP warrant upper gastrointestinal screening and surveillance endoscopy from the time of initial colonoscopy irrespective of referable symptoms. Patients with APC mutation between codon 1225-1694 may be more susceptible to aggressive gastroduodenal involvement in FAP.     

Germline and somatic mutations in exon 15 of the APC gene and K-ras mutations in duodenal adenomas in patients with familial adenomatous polyposis.

BACKGROUND: In sporadic colorectal adenomas mutations in the adenomatous polyposis gene (APC) are among the first gene aberrations to appear. In familial adenomatous polyposis (FAP) the patients already have a germline mutation in the APC gene. To investigate the natural history of duodenal adenomas in FAP patients, we examined germline and somatic mutations of the APC gene and K-ras mutations in these lesions. METHODS: Frozen sections from 54 duodenal polyps from 31 FAP patients were used to histologically verify the presence of adenomatous growth in the mucosa; the rest of each biopsy specimen was processed for DNA extraction. APC exon 15 was investigated with the protein truncation test (PTT), using four overlapping polymerase chain reaction (PCR) fragments, and samples showing an APC mutation were thereafter sequenced. The adenomas were examined for K-ras mutations by use of a combination of the 'enriched PCR method' and temporal temperature gradient electrophoresis. RESULTS: APC germline mutations in exon 15 were found in 19 of 31 (61%) patients, whereas somatic mutations were localized to 12 of 54 (22%) duodenal adenomas. In seven adenomas both the germline and the somatic mutations were found, whereas five small adenomas showed somatic mutations only. There was no tendency for more mutations to be detected in large and severely dysplastic adenomas compared with small and mildly dysplastic ones. K-ras mutations were found in four (7%) duodenal adenomas. CONCLUSIONS: The low rate of somatic APC and K-ras mutations in duodenal adenomas may indicate another neoplastic pathway than in FAP adenomas of the large bowel, or that a modifier gene is cosegregating with the disease.     

The most frequent APC mutations among Slovak familial adenomatous polyposis patients. Adenomatous polyposis coli

We screened 46 suspected families from whole Slovakia for familial adenomatous polyposis (FAP) cancer predisposition. Individuals were enrolled to the adenomatous polyposis coli (APC) gene mutations mapping program at the base of previous clinical investigation. We have used the following techniques: heteroduplex analysis (HDA), protein truncation test (PTT), single strand conformation polymorphism (SSCP) and sequencing for the identification and detailed positional analysis of APC mutations. Around 90% of all detected mutations were found being truncated. The most frequent mutations from this collection were located within codons 1309 and 1061 of exon 15 and represented 15% and 7%, respectively of all tested families. The expressive phenotype, large amount of colorectal polyps and congenital hypertrophy of the retinal pigment epithelium (CHRPE) were associated to all mutations within codons 1309 and 1060.     

Serrated adenoma in familial adenomatous polyposis: relation to germline APC gene mutation

BACKGROUND: Serrated adenoma is a precursor of colorectal cancer. AIM: To clarify possible genotype-phenotype correlations of serrated adenomas in familial adenomatous polyposis (FAP). Patients: Eleven patients from eight families with FAP. METHODS: We performed total colonoscopy with multiple biopsies in patients. Neoplasia with a serrated glandular structure was regarded as a serrated adenoma. In each patient, germline mutations of the APC gene were determined. Colonic phenotype was compared with germline mutations of the APC gene. RESULTS: Serrated adenomas were found in three patients. These patients had macroscopic polyps <100 in number. Pedigrees with serrated adenomas had the truncating germline APC mutation at codon 161, 332, or 1556 while in the other pedigrees mutations were found between codons 554 and 1324. CONCLUSIONS: In FAP, serrated adenoma may be a phenotype characteristic of the attenuated form.     

Osteomatous jaw lesions in familial adenomatous polyposis

The first aim of this study is to assess the frequency of osteomatous jaw lesions in patients with a diagnosis of familial adenomatous polyposis (FAP), and a group of FAP-relatives from the FAP registry of Majorca (Balearic Islands, Spain). The second aim is to study the predictive significance of osteomatous jaw lesions in families with FAP. The study included forty-two people. Twenty-five patients and seventeen relatives. All individuals underwent pantomography. Osteomatous jaw lesions were diagnosed in 68% of FAP-patients, and 6% of FAP-relatives. The difference was statistically significant (p < 0.001). The sensitivity was 68%, the specificity 94% and positive predictive value 94%. This frequency of osteomatous jaw lesions agree with previous studies of FAP-patients (57-82%), but differ from these of the previous studies of FAP-relatives (16-18%). The available method detect APC (adenomatous polyposis coli) gene mutations in 48-82% of FAP families. In the families without detected mutation, non-informative study or non-available study, the screening is based in seriated sigmoidoscopy and study of the extraintestinals lesions of the FAP syndrome. The frequency of osteomatous jaw lesions in FAP-patients is greater than the observed in FAP-relatives (p < 0.001). Osteomas in families with FAP are of predictive significance.     

Novel germline APC mutations in Swedish patients with familial adenomatous polyposis and Gardner syndrome

BACKGROUND: Familial adenomatous polyposis (FAP) is a familial cancer syndrome in which affected individuals develop multiple adenomatous polyps and are thereby at greatly increased risk of developing colorectal cancer. Gardner syndrome is a variant of FAP, in which the patients also develop extraintestinal tumors, in particular osteomas and desmoid tumors. An attenuated form of the disease (AFAP) is associated with fewer polyps, but still a high risk for colorectal cancer. Germline mutations in the adenomatosis polyposis coli (APC) gene cause FAP and Gardner syndrome and have recently been associated also with the development of AFAP. METHODS: We have analysed the entire APC gene for germline mutations in 7 patients with FAP and in 6 patients with suspected AFAP. Mutation screening was performed by direct sequencing of exons 1-14 and using the protein truncation test for analysis of exon 15. RESULTS: Novel disease-causing germline mutations, all of which resulted in truncation of the APC protein, were identified in 6 of the 7 patients with FAP or Gardner syndrome. No APC mutation was detected in any of the 6 patients with suspected AFAP. CONCLUSIONS: This study reports novel FAP- and Gardner syndrome-causing mutations in the APC gene. The lack of APC mutations in patients with multiple polyps at young age indicates that other genetic defects may cause this phenotype.     

The combination of heteroduplex analysis and protein truncation test for exact detection of the APC gene mutations

Familial adenomatous polyposis (FAP) is usually associated with mutation in the adenomatous polyposis coli (APC) gene. To examine the occurrence of these mutations in the number of FAP suspected families from the whole Slovakia effectively, we have applied heteroduplex analysis (HDA) and protein truncation test (PTT) for the analyses of 2-5 base pair deletions and point mutations of the APC gene. In the analyzed exon 15 of the APC gene determined by the primers 15Efor-15Grev for HDA and 15ET7-15J3 for PTT more than 70% of mutations should be deletions [3, 12], which are detectable by HDA. In our collection of 5 FAP families mutations in the APC gene were found in families 10, 27 and 41 using HDA. By PTT test the formation of truncated APC protein in FAP families 2, 10, 16 and 27 were revealed. The necessity of combination of at least HDA and PTT techniques for exact detection of APC mutations in analyzed APC region is discussed.