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).     

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.     

Thyroid carcinoma usually occurs in patients with familial adenomatous polyposis in the absence of biallelic inactivation of the adenomatous polyposis coli gene

Papillary thyroid carcinoma (PTC) is a rare extracolonic manifestation of familial adenomatous polyposis, determined by germline mutations of the adenomatous polyposis coli (APC) gene. The aim of this study was to assess the presence of loss of heterozygosity of APC in the thyroid tumoral tissue. Specimens from six female patients, aged 20-36, were analyzed for germline and somatic mutations of the APC gene by restriction enzyme analysis and sequence analysis. Five of the six also had analysis for ret/PTC, a chimeric gene, the activation of which is restricted to papillary TC. Because a previous study showed that germline mutations in familial adenomatous polyposis-associated thyroid carcinoma were located between codons 140 and 1513, the search for somatic mutations of the APC gene was restricted to this genomic area. Three of the six patients, belonging to the same kindred, had a germline mutation at codon 1061. The remaining three, one per kindred, had germline mutations at codons 1061, 1061, and 1309, respectively. None of the six patients had loss of heterozygosity for APC or somatic mutation in the explored genomic area (codon 545 and codons 1061-1678). Four of five had activation of ret/PTC in the thyroid tumoral tissue, as ret/PTC1 isoform. Either APC has a tissue-specific dominant effect in the thyroid gland or the germline mutation confers a generic susceptibility to cancer development, but other factors (sex-related factors, environmental radiation, modifier genes) are also required for TC development. This usually involves ret/PTC activation, suggesting a possible cooperation between altered function of APC and gain of function of ret.     

Can APC mutation analysis contribute to therapeutic decisions in familial adenomatous polyposis? Experience from 680 FAP families

BACKGROUND AND AIMS: In familial adenomatous polyposis (FAP), correlations between site of mutation in the adenomatous polyposis coli (APC) gene and severity of colonic polyposis or extracolonic manifestations are well known. While mutation analysis is important for predictive diagnosis in persons at risk, its relevance for clinical management of individual patients is open to question. METHODS: We examined 680 unrelated FAP families for germline mutations in the APC gene. Clinical information was obtained from 1256 patients. RESULTS: APC mutations were detected in 48% (327/680) of families. Age at diagnosis of FAP based on bowel symptoms and age at diagnosis of colorectal cancer in untreated patients were used as indicators of the severity of the natural course of the disease. A germline mutation was detected in 230 of 404 patients who were diagnosed after onset of bowel symptoms (rectal bleeding, abdominal pain, diarrhoea). When these patients were grouped according to the different sites of mutations, mean values for age at onset of disease differed significantly: patients carrying APC mutations at codon 1309 showed a disease onset 10 years earlier (mean age 20 years) compared with patients with mutations between codons 168 and 1580 (except codon 1309) (mean age 30 years), whereas patients with mutations at the 5' end of codon 168 or the 3' end of codon 1580 were diagnosed at a mean age of 52 years. Within each group of patients however large phenotypic variation was observed, even among patients with identical germline mutations. A higher incidence of desmoids was found in patients with mutations between codons 1445 and 1580 compared with mutations at other sites, while no correlation between site of mutation and presence of duodenal adenomas was observed. CONCLUSIONS: As age at manifestation and course of the disease may be rather variable, even in carriers of identical germline mutations, therapeutic decisions should be based on colonoscopic findings in individual patients rather than on the site of mutation. However, in patients with mutations within codons 1445-1580, it may be advisable to postpone elective colectomy because desmoids may arise through surgical intervention.     

Singapore familial adenomatous polyposis (FAP) patients with classical adenomatous polyposis but undetectable APC mutations have accelerated cancer progression

OBJECTIVES: Germline mutation in adenomatous polyposis coli (APC) is detected in up to 80% of familial adenomatous polyposis (FAP) patients worldwide. In this study, we evaluated clinical features and APC mutations of Singapore FAP patients and contrasted genotype-phenotype correlation with Caucasians from other regions of the world and between FAP patients with and without detectable APC mutations. METHODS: We screened 242 members from 57 unrelated FAP families using a combination of cDNA protein truncation test, multiplex ligation-dependent probe amplification, and differential expression techniques. RESULTS: APC germline mutations were detected in 50 families. In contrast to Caucasians, fundic gland polyposis in Singapore patients was associated with APC mutations throughout the coding region and osteomas were also not confined to codon 767-1573. There was also no FAP-associated hepatoblastoma or medullablastoma. APC mutation-negative patients from four families with mixed (adenomatous/hyperplastic/atypical juvenile) polyps were subsequently reclassified as hereditary mixed polyposis syndrome (HMPS) patients. APC mutation-negative patients with classical adenomatous polyposis were negative for MYH, beta-catenin, and Axin 1 mutations. These patients had a significantly older age at diagnosis (P < 0.001) and more colorectal cancers (P= 0.017) than patients with APC mutations. CONCLUSIONS: We achieved a 94% (50/53) APC mutation detection rate via a combination of techniques, suggesting that the current detection rate is probably not exhaustive. Singapore patients have some features similar to and other features distinct from Caucasians. Furthermore, APC mutation-negative patients have accelerated cancer progression that merits closer surveillance.     

The complex genotype-phenotype relationship in familial adenomatous polyposis

Familial adenomatous polyposis predisposes to colorectal cancer through multiple colorectal adenomas. The age of onset of adenomas and their number vary between families affected by this dominantly inherited trait, even within families. The same applies to a variety of associated manifestations including epidermoid cysts, osteomas, dental anomalies, desmoid tumours, retinal pigmentation and upper gastrointestinal polyps. The phenotype variation has a relationship with the site of truncating mutations on the APC gene. Thus, mutations at the mutation cluster region (codons 1250-1400) tend to cause early onset and severe polyposis whereas osteomas, dental changes and desmoids are most frequent in patients with the mutation 3' to codon 1400. The correlation observed, however, seems quite complex. Explanations may include variable interference of different mutant APC proteins on the wildtype APC function. There is also evidence suggesting an effect of modifier genes. The clinical applications of genotype-phenotype correlation on the management of patients with familial adenomatous polyposis remain limited apart from predictive genetic testing.     

The influence of mutation site and age on the severity of duodenal polyposis in patients with familial adenomatous polyposis

BACKGROUND: The present study was undertaken to identify factors affecting the severity of the duodenojejunal polyposis in patients with familial adenomatous polyposis. METHODS: Duodenojejunal polyposis was evaluated in 41 consecutive patients with familial adenomatous polyposis (mean age 41 years, range 21-63 years), 33 (80%) with known APC mutation, by using a standardized endoscopic protocol. The severity of the polyposis was graded with the Spigelman scoring system (0-12 points), the Spigelman score/age ratio, and the presence or absence of advanced adenomas (>1 cm in diameter and/or high-grade dysplasia). RESULTS: The Spigelman score (median 8, range 3-12) was higher in patients older than 50 years (median 10, range 3-12) as compared with younger patients (median 7.5, range 3-11; p = 0.043). A significant association between age and the presence of advanced adenomas was also observed. Patients with a mutation in the central part of the APC gene (codons 279-1309) had a higher Spigelman score and Spigelman score/age ratio as compared with patients with other mutations: median Spigelman score/age ratio 0.21 (range 0.14-0.40) versus 0.10 (range 0.06-0.20) (p < 0.001). CONCLUSIONS: Older age and APC mutation in the central part of the gene are risk factors for the development of severe duodenojejunal polyposis.     

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.     

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.     

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

     

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.     

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.     

Germ-line mutations of the APC gene in 53 familial adenomatous polyposis patients.

We searched for germ-line mutations of the APC gene in 79 unrelated patients with familial adenomatous polyposis using a ribonuclease protection analysis coupled with polymerase chain reaction amplifications of genomic DNA. Mutations were found in 53 patients (67%); 28 of the mutations were small deletions and 2 were 1- to 2-base-pair insertions; 19 were point mutations resulting in stop codons and only 4 were missense point mutations. Thus, 92% of the mutations were predicted to result in truncations of the APC protein. More than two-thirds (68%) of the mutations were clustered in the 5' half of the last exon, and nearly two-fifths of the total mutations occurred at one of five positions. This information has significant implications for understanding the role of APC mutation in inherited forms of colorectal neoplasia and for designing effective methods for genetic counseling and presymptomatic diagnosis.     

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.     

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.     

Presymptomatic diagnosis of familial adenomatous polyposis coli

Familial adenomatous polyposis (FAP), an autosomal dominant inherited disease, confers a high risk of colon cancer, and recently the gene responsible for FAP, termed adenomatous polyposis coli (APC) gene, was identified and fully characterized. PURPOSE: For the presymptomatic diagnosis of FAP, we have performed linkage studies using two polymorphic systems close to or at the APC locus; cytosine-adenine dinucleotide repeat length polymorphism and restriction endonuclease RsaI site polymorphism. METHODS and RESULTS: Based on the two polymorphic systems, we have determined the haplotype at the APC locus in 23 individuals of two Korean families with FAP. From these haplotypes of individuals, we could make the diagnosis, whether affected or unaffected, in 74 percent of 31 at-risk persons. To decrease the chance of misdiagnosis caused by recombinant events, the use of haplotypes was better than using one polymorphic system. In addition to polymorphic analysis, we have also searched germline mutations of the APC gene in eight individuals (26 percent of all 31 at risk persons) of another two FAP families which could not be diagnosed definitely by linkage analysis. A 5 base-pairs deletion at codon 1309 was detected in one of the families, and a 5 base-pairs deletion at codon 1185 was also identified in another family by using a ribonuclease protection assay followed by DNA sequencing. From these results, we could diagnose FAP with 100 percent accuracy. CONCLUSION: Linkage studies by the Rsa I site polymorphism and cytosine-adenine repeat length polymorphism as well as the polymerase chain reaction-based sequencing method provide accurate and efficient tools for presymptomatic diagnosis of FAP in their families.Supported in part by a grant from the Seoul National University Hospital Research Fund (04-93-007) and a grant from Korea Science and Engineering Foundation (KOSEF-SRC-56-CRC-8).Read at the meeting of The American Society of Colon and Rectal Surgeons, Chicago, Illinois, May 2 to 7, 1993.     

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.     

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 Mutation Spectrum of the <Emphasis Type="Italic">APC</Emphasis> Gene in Turkish Patients with Familial Adenomatous Polyposis

Purpose Familial adenomatous polyposis, an autosomal-dominant disease characterized by the presence of 100 or more colorectal adenomatous polyps, results from mutations in the adenomatous polyposis coli tumor suppressor gene. This study was designed to investigate adenomatous polyposis coli gene mutations in members of Turkish families with familial adenomatous polyposis to constitute an adenomatous polyposis coli mutation spectrum for the Turkish population and to determine specific biomarkers for use in the early diagnosis of familial adenomatous polyposis. Methods We investigated adenomatous polyposis coli gene mutations in six unrelated families with familial adenomatous polyposis by using heteroduplex analysis and DNA sequencing. Results We identified three different mutations in six families. Of these one is known and two are novel: 1018T>C and 1309delGAAAA. The mutation of a T to C transversion at codon 1018 does not cause an alteration in the meaning of the codon; however, it was determined that this silent mutation does cause the formation of new exonic splicing enhancers (ESEs) motifs on a mutated sequence by using ESEfinder program. Conclusions This study contributes to enlarging the adenomatous polyposis coli gene mutations spectrum and to defining new biomarkers for the early diagnosis of Turkish patients with familial adenomatous polyposis. Supported by Society of Investigation and Prevention of Genetic Diseases. Reprints are not available.     

Attenuated familial adenomatous polyposis: an evolving and poorly understood entity.

PURPOSE: Familial adenomatous polyposis is a well-described, autosomal dominant, inherited syndrome characterized by diffuse polyposis of the colon and rectum as well as various upper gastrointestinal and extraintestinal manifestations. A subset of patients present with fewer colorectal polyps, later age of onset of polyps and cancer, and a predilection toward involvement of the proximal colon. This variant of familial adenomatous polyposis is known as attenuated familial adenomatous polyposis. The purpose of this review is to summarize current knowledge regarding this poorly understood entity and propose guidelines for diagnosis, surveillance, and surgical management. METHODS: The MEDLINE database was searched from 1985 onward using the keywords, "attenuated familial adenomatous polyposis," "AFAP," "adenomatous polyposis coli gene," and "APC gene." Additional articles were identified through the reference sections of retrieved papers. All papers that pertained to attenuated familial adenomatous polyposis or mutations in the APC gene producing an attenuated phenotype were included. RESULTS: Attenuated familial adenomatous polyposis is transmitted in an autosomal dominant fashion. Several distinct mutations within the APC gene have been associated with an attenuated phenotype, but variability of disease expression within kindreds possessing identical mutations makes classification difficult. Polyps are diagnosed at a mean age of 44 years, with cancer diagnosed at a mean of 56 years of age. Frequent involvement of the proximal colon necessitates the use of colonoscopy for surveillance, and infrequent involvement of the rectum supports the role of a total abdominal colectomy and ileorectal anastomosis. CONCLUSIONS: Although currently recognized as a distinct clinical entity, attenuated familial adenomatous polyposis may be part of a spectrum of disease that includes familial adenomatous polyposis and is caused by different mutations within the APC gene. Because of its unique characteristics, yet apparent overlap with familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, increased awareness of attenuated familial adenomatous polyposis should improve diagnosis, surveillance, and treatment strategies in this unique subset of familial polyposis syndromes.