APC gene mutations causing familial adenomatous polyposis in Polish patients

An update of the variant spectrum of the APC gene in Iranian familial adenomatous polyposis patients

Familial adenomatous polyposis (FAP) is an autosomal dominant colorectal cancer syndrome that is characterized by the development of multiple adenomas in the colon and rectum with high penetrance rates. This disease has specific features like the occurrence of pathogenic variations in the APC gene and diverse FAP phenotypes due to the occurrence region. In this study we aimed to evaluate pathogenic variants in exons of the APC gene in Iranian patients with FAP. A total of 35 FAP individuals were referred to the gastroenterology ward of Taleghani Hospital. As the aim of the study was to study the germline variations in the participants, the peripheral blood was collected and after the DNA extraction, PCR, and Sanger sequencing processes for the APC gene, the results were evaluated by the ACMG classification guidelines to report their pathogenicity. Accordingly, out of eight specific detected variants, three of them were novel, and the rest were reported previously. These eight variants were all truncating protein and pathogenic, and they were limited to 849-1378 codons. Overall, detected variants revealed discrepancies and parallels with previous reported cases in terms of quantity, occurrence region, and association with demographic and clinicopathological characteristics of patients. The spectrum of detected variants and the patient's phenotype showed distinct characteristics, such as occurrence in specific regions and the absence of extracolonic symptoms like Congenital hypertrophy of the retinal pigment epithelium (CHRPE). These findings open the path to comprehending the typical symptoms, their rarity, and their occurrence in the Iranian population and also due to the facts, we found that the studying of the APC gene alone for diagnosing FAP disease is not sufficient, and considering other genes are completely rational in the case of sequencing and studying the variants.

Germline mutations of the adenomatous polyposis coli (APC) gene in Algerian familial adenomatous polyposis cohort: first report

BACKGROUND

Familial adenomatous polyposis (known also as classical or severe FAP) is a rare autosomal dominant colorectal cancer predisposition syndrome, characterized by the presence of hundreds to thousands of adenomatous polyps in the colon and rectum from an early age. In the absence of prophylactic surgery, colorectal cancer (CRC) is the inevitable consequence of FAP. The vast majority of FAP is caused by germline mutations in the adenomatous polyposis coli (APC) tumor suppressor gene (5q21). To date, most of the germline mutations in classical FAP result in truncation of the APC protein and 60% are mainly located within exon 15.

MATERIAL AND METHODS

In this first nationwide study, we investigated the clinical and genetic features of 52 unrelated Algerian FAP families. We screened by PCR-direct sequencing the entire exon 15 of APC gene in 50 families and two families have been analyzed by NGS using a cancer panel of 30 hereditary cancer genes.

RESULTS

Among 52 FAP index cases, 36 had 100 or more than 100 polyps, 37 had strong family history of FAP, 5 developed desmoids tumors, 15 had extra colonic manifestations and 21 had colorectal cancer. We detected 13 distinct germline mutations in 17 FAP families. Interestingly, 4 novel APC germline pathogenic variants never described before have been identified in our study.

CONCLUSIONS

The accumulating knowledge about the prevalence and nature of APC variants in Algerian population will contribute in the near future to the implementation of genetic testing and counseling for FAP patients.

A Case of Adult Pancreatoblastoma With Novel APC Mutation and Genetic Heterogeneity

Background

Pancreatoblastoma is a rare malignant epithelial neoplasm of the pancreas that mainly occurs in children and involves abnormalities in the WNT/β-catenin pathway, such as CTNNB1 mutation. However, the molecular abnormalities in adult pancreatoblastoma are not well known.

Case Presentation

An elderly man, who underwent elective distal pancreatectomy and splenectomy, was referred to our hospital with a mass in the tail of the pancreas. Histologically, the lesion revealed proliferation of clear, basophilic, and cartilaginous tumor cells with lymphatic metastasis. Each of the morphologically distinct tumor components showed different immunohistochemical patterns, indicating heterogeneous differentiation, including epithelial (both acinar and ductal), mesenchymal, and neuroendocrine differentiation. All tumor components showed nuclear expression of β-catenin and cyclin D1. Per next-generation sequencing (NGS), the clear and basophilic tumor cells shared mutations in APC, GRM8, LAMP1, and AKA9. Among the mutations, APC, c.1816_1817insA showed the highest frequency in both cell types, indicating that APC mutation was a driver mutation of the tumor. A diagnosis of PB was rendered.

Summary

In conclusion, the clear and basophilic cells of the tumor were supposedly derived from the same clone and subsequently acquired additional mutations. This is the first report of clonal evolution in pancreatoblastoma.

Mutational Analysis of a Familial Adenomatous Polyposis Pedigree with Bile Duct Polyp Phenotype

A large number of colorectal cancers have a genetic background in China. However, due to insufficient awareness, the diagnostic rate remains low and merely 5-6% of colorectal cancer patients are diagnosed with hereditary colorectal cancer. Familial adenomatous polyposis (FAP) is an autosomal dominant genetic disease caused by mutations in the adenomatous polyposis coli (APC) gene. Different mutation sites in APC are associated with the severity of FAP, risks of carcinogenesis, and extraintestinal manifestations. We used next-generation sequencing (NGS) and capture techniques to screen suspected mutation points in the proband in this pedigree. Using modified Sanger sequencing, we identified members of the family who were carriers of this variant and whether this segregated well with disease occurrence. FAP family members had multiple adenomatous polyps in their gastrointestinal tracts, some of which developed into cancer with age. Two subjects presented a rare common bile duct polyp phenotype. No extraintestinal manifestations were observed. A heterozygous frameshift mutation in APC exon 16 (NM_000038.6) was observed in the proband and in other patients: c.3260_3261del (p.Leu1087GlnQfs ^∗ 31) (rs587782305); the variant call format was CCT/C. Due to the deletion of two bases, a stop codon appeared after 31 amino acids, and the protein was truncated prematurely, which affected the conformation of the protein. Pedigree genetic linkage analysis showed that the clinical phenotype cosegregated with the APC mutation p.L1087fs. This mutation may be the pathogenic in this FAP family and responsible for this rare common bile duct polyp.

Mutational screening through comprehensive bioinformatics analysis to detect novel germline mutations in the APC gene in patients with familial adenomatous polyposis (FAP)

Background

Familial adenomatous polyposis (FAP) as a colon cancer predisposition syndrome is an autosomal‐dominant inherited condition and is diagnosed by the progress of hundreds or thousands of adenomatous colonic polyps in the colon. This study aims at the nature and effect of Adenomatous Polyposis Coli (APC) gene mutations in FAP tumorigenesis.

Methods

The genetic screening of 59 FAP Iranian patients in 10 families was performed by polymerase chain reactions and the direct sequencing of the entire coding exons of the APC gene. To do linkage haplotype analysis and multiplex PCR‐based microsatellite examination, six short tandem repeat loci were selected in this gene. To evaluate and predict the potentially deleterious effects, comprehensive bioinformatics pathogenicity assays were used.

Results

A total of 12 germline heterozygous and homozygous nucleotide variations were identified. They included two missense mutations, four nonsense mutations, which would lead to the truncated and nonfunctional protein products, four synonymous or silent variations, and two nucleotide deletions of 1 to 5 bp or frameshift mutations. In addition, three novel heterozygous nonsense mutations were found in exons 10, 14, and 15 of the gene. There was also p.Arg653Met as a novel heterozygote mutation in exon 14 of the gene.

Conclusions

Bioinformatics analysis and three‐dimensional structural modeling predicted that these missense and nonsense mutations generally are associated with the deleted or truncated domains of APC and have functional importance and mainly affected the APC protein. These findings may provide evidence for the progress of potential biomarkers and help to understand the role of the APC gene in FAP.

APC Splicing Mutations Leading to In-Frame Exon 12 or Exon 13 Skipping Are Rare Events in FAP Pathogenesis and Define the Clinical Outcome

Familial adenomatous polyposis (FAP) is caused by germline mutations in the tumor suppressor gene APC. To date, nearly 2000 APC mutations have been described in FAP, most of which are predicted to result in truncated protein products. Mutations leading to aberrant APC splicing have rarely been reported. Here, we characterized a novel germline heterozygous splice donor site mutation in APC exon 12 (NM_000038.5: c.1621_1626+7del) leading to exon 12 skipping in an Italian family with the attenuated FAP (AFAP) phenotype. Moreover, we performed a literature meta-analysis of APC splicing mutations. We found that 119 unique APC splicing mutations, including the one described here, have been reported in FAP patients, 69 of which have been characterized at the mRNA level. Among these, only a small proportion (9/69) results in an in-frame protein, with four mutations causing skipping of exon 12 or 13 with loss of armadillo repeat 2 (ARM2) and 3 (ARM3), and five mutations leading to skipping of exon 5, 7, 8, or (partially) 9 with loss of regions not encompassing known functional domains. The APC splicing mutations causing skipping of exon 12 or 13 considered in this study cluster with the AFAP phenotype and reveal a potential molecular mechanism of pathogenesis in FAP disease.

Pathogenic APC Variants in Latvian Familial Adenomatous Polyposis Patients

Background and objectives: Familial adenomatous polyposis is one of the APC-associated polyposis conditions described as genetically predetermined colorectal polyposis syndrome with a variety of symptoms. The purpose of this study was to determine sequence variants of the APC gene in patients with familial adenomatous polyposis (FAP) phenotype and positive or negative family history. Materials and Methods: Eight families with defined criteria of adenomatous polyposis underwent molecular genetic testing. Coding regions and flanking intron regions of the APC gene were analyzed by Sanger sequencing. Results: Eight allelic variants of the APC gene coding sequence were detected. All allelic variants of the APC gene were predicted to be pathogenic based on criteria according to the “Joint Consensus Recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology” (2015), four of them c.1586_1587insAT, c.2336delT, c.3066_3067insGA, and c.4303_4304insC, were considered novel. Conclusions: The timely molecular genetic analysis of APC germline variants and standardized interpretation of the pathogenicity of novel allelic variants has a high impact on choice for treatment, cancer prevention, and family genetic counseling.

Mutation Spectrum of Cancer-Associated Genes in Patients With Early Onset of Colorectal Cancer

Background: Colorectal cancer (CRC) incidence is rising worldwide, as well as in the Republic of Kazakhstan, while its occurrence is also increasing in the younger population. Hereditary forms associated with the development of colon and rectal cancer and early-onset CRC have never been studied in the population of Kazakhstan. The aim of this research was to investigate the spectrum of CRC-related gene mutations to determine which mutations cause early onset of CRC in the Kazakhstan population.

Methods: The study included 125 unrelated patients from Kazakhstan (range 17–50 years in age) with early onset CRC. Genomic DNA was obtained from peripheral blood of the patients. Next-generation sequencing was performed using the TruSightCancer Kit on the MiSeq platform. The Studio Variant was used to annotate and interpret genetic variants.

Results: Bioinformatics analysis of Next-generation sequencing data revealed 11,152 variants from 85 genes, of them, 3,790 missense, 6,254 synonymous variants, 44 3′UTR variants, 10 frameshift variants, five stop-gain variants, four in-frame deletions, two splice donors, one splice acceptor variant, and 1,042 intron or non-coding variants. APC, BRCA2/1, ALK, BRIP1, EGFR, FANCA, FANCD2, FANCI, HNF1A, MEN1, NSD1, PMS2, RECQL4, RET, SLX4, WRN, and XPC genes mutated most often. According to the ACMG guidelines and LOVD/ClinVar databases, 24 variants were pathogenic (10 frameshifts, five missenses, five stop-gain, one in-frame deletion, and three splice-site mutations), and 289 were VUS with population frequency <1%, 131 of them were attributed as deleterious. In the study, 50% of all pathogenic mutations found in Kazakhstani patients with early CRC onset were identified in the subgroups with a family history of CRC and primary multiple tumors. In APC, pathogenic mutations were most often (21%).

Conclusion: Pathogenic and likely pathogenic mutations were found in 20 (16%) out of 125 patients. Eight novel pathogenic mutations detected in FANCI, APC, BMPR1, ATM, and DICER1 genes have not been reported in previous literature. Given the high frequency and wide spectrum of mutations, NGS analysis must be carried out in families with a history of CRC/CRC-related cancers with the purpose to identify cause-effective mutations, clarify the clinical diagnosis, and prevent the development of the disease in other family members.

Advances in Identification of Susceptibility Gene Defects of Hereditary Colorectal Cancer

Colorectal cancer (CRC) is a common malignant tumor of the digestive system worldwide, associated with hereditary genetic features. CRC with a Mendelian genetic predisposition accounts for approximately 5-10% of total CRC cases, mainly caused by a single germline mutation of a CRC susceptibility gene. The main subtypes of hereditary CRC are hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). With the rapid development of genetic testing methods, especially next-generation sequencing technology, multiple genes have now been confirmed to be pathogenic, including DNA repair or DNA mismatch repair genes such as APC, MLH1, and MSH2. Since familial CRC patients have poor clinical outcomes, timely clinical diagnosis and mutation screening of susceptibility genes will aid clinicians in establishing appropriate risk assessment and treatment interventions at a personal level. Here, we systematically summarize the susceptibility genes identified to date and the potential pathogenic mechanism of HNPCC and FAP development. Moreover, clinical recommendations for susceptibility gene screening, diagnosis, and treatment of HNPCC and FAP are discussed.

A novel pathogenic large germline deletion in adenomatous polyposis coli gene in a Chinese family with familial adenomatous polyposis

Germline mutations of the APC gene are associated with an autosomal dominant precancerous condition, termed familial adenomatous polyposis (FAP). FAP is clinically manifested by the presence of multiple colorectal adenomas or polyps. Gradually, these colorectal adenomas or polyps inevitably result in colorectal cancer by the third-to fourth decade of life. Surgical interventions or total proctocolectomy is the best possible treatment for FAP. Here, we present a clinical molecular study of a five generation Chinese family with FAP. Diagnosis of FAP was made on the basis of clinical manifestations, family history and medical (colonoscopy and histopathology) records. Blood samples were collected and genomic DNA was extracted. Genetic screening of the APC gene was performed by targeted next-generation sequencing and quantitative real-time PCR. Targeted next generation sequencing identified a novel heterozygous large deletion [exon5-exon16; c.423_8532del] of APC gene, which segregated with the FAP phenotypes in the proband and in all the affected family members. Unaffected family members and normal controls did not carry this deletion. In the Chinese population, most of the previously reported APC gene mutations are missense mutations. This is the first report describing the largest deletion of the APC gene in the Chinese population associated with FAP.

First-decade patient with colorectal cancer carrying both germline and somatic mutations in APC gene

Background

Colorectal carcinoma (CRC) is one of the most common causes of cancer-related deaths. The mean age of patients with CRC ranges from 49 to 60 years. Pediatric CRC is unusual, which often escapes early diagnosis because of a lack of awareness of its occurrence in children. The association between the mutation of APC and the occurrence of CRC in the first decade of life remains unknown.

Case presentation

We report a 10-year-old child with CRC; he was diagnosed with stage IIIB advanced transverse colon cancer without distal metastases. We detected a heterozygous germline mutation at c.5465 T > A in both blood and tissue samples and a heterozygous somatic mutation at c.7397C > T in the tissue sample. Both of these mutations can cause CRC tumorigenesis in the first decade of life.

Conclusions

The rare genetic features of this 10-year-old patient might be the predisposing cause of pediatric CRC. Therefore, screening patients with early-onset CRC through clinical and genetic characterizations is suggested.

A novel pathogenic splice acceptor site germline mutation in intron 14 of the APC gene in a Chinese family with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant precancerous condition, clinically characterized by the presence of multiple colorectal adenomas or polyps. Patients with FAP has a high risk of developing colorectal cancer (CRC) from these colorectal adenomatous polyps by the mean age of diagnosis at 40 years. Germline mutations of the APC gene cause familial adenomatous polyposis (FAP). Colectomy has recommended for the FAP patients with significant polyposis. Here, we present a clinical molecular study of a four generation Chinese family with FAP. Clinical diagnosis of FAP has been done according to the phenotype, family history and medical records. Patient's blood samples were collected and genomic DNA was extracted. In order to identify the pathogenic mutation underlying the disease phenotype targeted next-generation sequencing and confirmatory sanger sequencing has undertaken. Targeted next generation sequencing identified a novel heterozygous splice-acceptor site mutation [c.1744-1G>A] in intron 14 of APC gene, which is co-segregated with the FAP phenotypes in the proband and amongst all the affected family members. This mutation is not present in unaffected family members and in normal healthy controls of same ethnic origin. According to the LOVD database for Chinese colorectal cancer patients, in Chinese population, 60% of the previously reported APC gene mutations causes FAP, are missense mutations. This novel splice-acceptor site mutation causing FAP in this Chinese family expands the germline mutation spectrum of the APC gene in the Chinese population.

Exploitation of Gene Expression and Cancer Biomarkers in Paving the Path to Era of Personalized Medicine

Cancer therapy agents have been used extensively as cytotoxic drugs against tissue or organ of a specific type of cancer. With the better understanding of molecular mechanisms underlying carcinogenesis and cellular events during cancer progression and metastasis, it is now possible to use targeted therapy for these molecular events. Targeted therapy is able to identify cancer patients with dissimilar genetic defects at cellular level for the same cancer type and consequently requires individualized approach for treatment. Cancer therapy begins to shift steadily from the traditional approach of “one regimen for all patients” to a more individualized approach, through which each patient will be treated specifically according to their specific genetic defects. Personalized medicine accordingly requires identification of indicators or markers that guide in the decision making of such therapy to the chosen patients for more effective therapy. Cancer biomarkers are frequently used in clinical practice for diagnosis and prognosis, as well as identification of responsive patients and prediction of treatment response of cancer patient. The rapid breakthrough and development of microarray and sequencing technologies is probably the main tool for paving the way toward “individualized biomarker-driven cancer therapy” or “personalized medicine”. In this review, we aim to provide an updated knowledge and overview of the current landscape of cancer biomarkers and their role in personalized medicine, emphasizing the impact of genomics on the implementation of new potential targeted therapies and development of novel cancer biomarkers in improving the outcome of cancer therapy.

Novel mutations and phenotypic associations identified through APC, MUTYH, NTHL1, POLD1, POLE gene analysis in Indian Familial Adenomatous Polyposis cohort

Colo-Rectal Cancer is a common cancer worldwide with 5-10% cases being hereditary. Familial Adenomatous Polyposis (FAP) syndrome is due to germline mutations in the APC or rarely MUTYH gene. NTHL1, POLD1, POLE have been recently reported in previously unexplained FAP cases. Unlike the Caucasian population, FAP phenotype and its genotypic associations have not been widely studied in several geoethnic groups. We report the first FAP cohort from South Asia and the only non-Caucasian cohort with comprehensive analysis of APC, MUTYH, NTHL1, POLD1, POLE genes. In this cohort of 112 individuals from 53 FAP families, we detected germline APC mutations in 60 individuals (45 families) and biallelic MUTYH mutations in 4 individuals (2 families). No NTHL1, POLD1, POLE mutations were identified. Fifteen novel APC mutations and a new Indian APC mutational hotspot at codon 935 were identified. Eight very rare FAP phenotype or phenotypes rarely associated with mutations outside specific APC regions were observed. APC genotype-phenotype association studies in different geo-ethnic groups can enrich the existing knowledge about phenotypic consequences of distinct APC mutations and guide counseling and risk management in different populations. A stepwise cost-effective mutation screening approach is proposed for genetic testing of south Asian FAP patients.

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.

Familial Adenomatous Polyposis; 30-Year Observation of a Female Patient - Case Report

Familial adenomatous polyposis (FAP) is a colorectal cancer syndrome caused by a germline mutation inherited in an autosomal-dominant pattern with a 100% penetrance. Our detailed case report presents a history of a 55-year-old FAP female patient who had been under constant clinical observation for 30 years. The disease was diagnosed at the age of 22. The patient underwent restorative proctocolectomy with ileal pouch-anal anastomosis (PRC-IPAA). During our follow-up extra-colonic manifestations occurred such as a desmoidtumour, fundic gland polyps in the stomach and duodenal polyps also in the periampullary region. Apart from disease-related symptoms the patient manifested other complications such as small bowel adhesive obstruction, benign breast tumours, uterine myomas, cholelithiasisand thyroid nodules. Our analysis of the above case presents advantages of a long-term medical observation of a FAP patient carried out by a specialist surgical medical centre.

Prognostic and predictive biomarkers: tools in personalized oncology

Oncology indispensably leads us to personalized medicine, which allows an individual approach to be taken with each patient. Personalized oncology is based on pharmacogenomics and the effect of genetic differences in individuals (germline and somatic) on the way cancer patients respond to chemotherapeutics. Biomarkers detected using molecular biology tools allow the molecular characterization of cancer signatures and provide information relevant for personalized treatment. Biomarkers can be divided into two main subgroups: prognostic and predictive. The aim of the application of prognostic biomarkers, which provide information on the overall cancer outcome in patients, is to facilitate cancer diagnosis, usually with no need for putting invasive methods into use. Predictive biomarkers help to optimize therapy decisions, as they provide information on the likelihood of response to a given chemotherapeutic. Among the prognostic factors that identify patients with different outcome risks (e.g., recurrence of the disease), the following factors can be distinguished: somatic and germline mutations, changes in DNA methylation that lead to the enhancement or suppression of gene expression, the occurrence of elevated levels of microRNA (miRNA) capable of binding specific messenger RNA (mRNA) molecules, which affects gene expression, as well as the presence of circulating tumor cells (CTCs) in blood, which leads to a poor prognosis for the patient. Biomarkers for personalized oncology are used mainly in molecular diagnostics of chronic myeloid leukemia, colon, breast and lung cancer, and recently in melanoma. They are successfully used in the evaluation of the benefits that can be achieved through targeted therapy or in the evaluation of toxic effects of the chemotherapeutic used in the therapy.

Comparative‑high resolution melting: a novel method of simultaneous screening for small mutations and copy number variations

Efficient and cost-effective screening for DNA sequence changes, both small mutations and copy number variations (CNVs), is a crucial aspect for routine genetic diagnostics as well as for basic research. In this study we present a development and evaluation of comparative-high resolution melting (C-HRM), a new approach for the simultaneous screening of small DNA changes and gene CNVs. In contrast to other methods, relative quantification in C-HRM is based on the results obtained during the melting process and calculations of the melting peak height ratio in the multiplex reaction. Validation of the method was conducted on DNA samples from 50 individuals from Duchenne muscular dystrophy (DMD) families, 50 probands diagnosed with familial adenomatous polyposis and a control group of 36 women and 36 men. The results of analyses conducted on fragments of the DMD and APC genes correspond completely (100 %) with the results of previous studies. C-HRM sensitivity in CNV detection was assessed through the analysis of mixed DNA samples with different proportions of a deletion carrier and wild type control. The results are presented as a linear regression with R² of 0.9974 and imply the capability of the method to detect mosaics. C-HRM is an attractive and powerful alternative to other methods of point mutations and CNV detection with 100 % accuracy in our studied group.

Familial adenomatous polyposis of the colon

Familial adenomatous polyposis (FAP) is a well-defined autosomal dominant predisposition to the development of polyposis in the colon and rectum at unusually early ages. The first symptoms of FAP are diarrhea and blood in the stool. Weight loss and weaknesses occur after the development of advanced tumour. The incidence of the FAP disorder is one per 10000 newborns. There are high levels of heterogeneity with regard to the number and timing of the occurrence of polyps. The classical form of FAP is characterized by the presence of more than 100 polyps, which appear in the second decade of life. The average time of occurrence of polyps is 15 years. The earliest symptoms of polyposis have been observed in a three-year-old child. The polyps are characterized by large potential for the development towards malignant tumour. Malignancy can occur from late childhood onwards. Attenuated adenomatous polyposis coli is characterized by a more benign course of disease in contrast to classical FAP. The occurrence of FAP is associated with mutations in the APC tumour suppressor gene, which was described in 1991. The APC gene is located on chromosome 5q21 and is involved in cell proliferation control. A recessive form of adenomatous polyposis is caused by mutations in the base excision repair gene - MUTYH gene. The MUTYH gene is involved in repairing DNA lesions as a result of oxidative DNA damage. MUTYH associated polyposis (MAP) is a predisposition to the development of polyps of the colon but the number of polyps is lower in comparison to classical FAP. The high risks of cancer observed in these two diseases make them important medical issues. Molecular studies of colonic polyposis have been performed in Poland for over fifteen years. A DNA Bank for Polish FAP patients was established at the Institute of Human Genetics in Poznan in which DNA samples from 600 FAP families have been collected.

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.

Clinical and genetic spectrum of Birt-Hogg-Dube syndrome patients in whom pneumothorax and/or multiple lung cysts are the presenting feature

BACKGROUND

Birt-Hogg-Dubé syndrome (BHDS) is an inherited autosomal genodermatosis characterised by fibrofolliculomas of the skin, renal tumours and multiple lung cysts. Genetic studies have disclosed that the clinical picture as well as responsible germline FLCN mutations are diverse.

OBJECTIVES

BHDS may be caused by a germline deletion which cannot be detected by a conventional genetic approach. Real-time quantitative polymerase chain reaction (qPCR) may be able to identify such a mutation and thus provide us with a more accurate clinical picture of BHDS.

METHODS

This study analysed 36 patients with multiple lung cysts of undetermined causes. Denaturing high performance liquid chromatography (DHPLC) was applied for mutation screening. If no abnormality was detected by DHPLC, the amount of each FLCN exon in genome was quantified by qPCR.

RESULTS

An FLCN germline mutation was found in 23 (63.9%) of the 36 patients by DHPLC and direct sequencing (13 unique small nucleotide alterations which included 11 novel mutations). A large genomic deletion was identified in two of the remaining 13 patients by qPCR (one patient with exon 14 deletion and one patient with a deletion encompassing exons 9 to 14). Mutations including genomic deletions were most frequently identified in the 3'-end of the FLCN gene including exons 12 and 13 (13/25=52.0%). The BHDS patients whose multiple cysts prompted the diagnosis in this study showed a very low incidence of skin and renal involvement.

CONCLUSIONS

BHDS is due to large deletions as well as small nucleotide alterations. Racial differences may occur between Japanese and patients of European decent in terms of FLCN mutations and clinical manifestations.

Combined iPLEX and TaqMan assays to screen for 45 common mutations in Lynch syndrome and FAP patients

Mutations of genes associated with the mismatch repair mechanism and mutations of the APC gene are the most frequent causes of hereditary colorectal cancer. An iPLEX test combined with TaqMan genotyping assays was therefore developed to identify common recurrent mutations of those genes in the Polish population. We analyzed 349 DNA samples from 95 positive controls previously identified by sequencing and 254 unexamined individuals. The iPLEX test included two plexes, which comprised seven mutations of the APC gene and 29 mutations of three of the mismatch repair genes. TaqMan assays were designed for nine mutations not covered by the iPLEX assays: one mutation in the APC gene and eight mutations in the mismatch repair genes. Results were then verified independently by sequencing. Our combination method allowed detection of all recurrent mutations occurring in group of patients, followed by full analysis by DNA sequencing. With the exception of one false positive in the iPLEX test in the positive control group that could be assigned to contamination from neighboring wells rather than a detection error, given sufficient DNA concentration and quality, the designed iPLEX/TaqMan test had an accuracy of 100% for the designed assays. These results suggest that the combined iPLEX/TaqMan test is an outstanding tool for identification of recurrent mutations among hereditary colorectal cancer patients.