Genetic evidence that Turcot syndrome is not allelic to familial adenomatous polyposis

Possible Considerations for the Management of Turcot’s Syndrome?

Background:

Turcot’s syndrome (TS) is a rare disease with known incidence of about 1-2 cases per year. It is, however, linked to high mortality due to the brain cancer. And because of this, we propose recommendations, aimed at preventing the mortality of the patients and to minimize the risk of undiagnosed Turcot’s syndrome.

Methods:

The authors collected the worldwide published data on TS, from the year of its definition till 2018, all of which was published on the search engines, such as Medline, Medknow, Cohraine and Wiley.

Results:

We included 97 patients, 57 from which are females and 40 males with median age of 22 years. The most common type of cancer is medulloblastoma, followed by glioblastoma and astrocytoma. We further divided the patients into two categories based on the first symptom of the disease and we made an algorithm of approaching these patients.

Conclusion:

TS is a disease that affects mostly members of families with multiple genetic mutations and types of cancers. And because of the unknown mechanisms of inheritance, it is useful to establish guidelines for the approach of those patients, in order to minimize the high mortality rate.

[Muir-Torre syndrome and Turcot syndrome]

INTRODUCTION

Lynch syndrome (LS) is a syndrome that carries a genetic predisposition to certain cancers associating, either in a single individual or in a family, a visceral tumour, mainly colorectal, with a high risk of other synchronous or metachronous cancers. LS is linked with mutations in the genes coding for proteins in the DNA repair system. Phenotypic variants of SL exist, including Muir-Torre syndrome (MTS) and Turcot syndrome (TS), both of which predispose to colorectal cancer. They may be distinguished by the presence of benign or malignant sebaceous tumours in MTS, and tumours of the central nervous system in TS.

PATIENTS AND METHODS

A 59-year-old man, with a history of right colon cancer at the age of 36 years, consulted for a nose lesion shown by histopathological examination to be a sebaceous tumour. Immunohistochemistry revealed loss of expression of proteins MSH2 and MSH6, strongly suggesting a diagnosis of MTS. Eight years earlier, the man's son had developed a fatal glioblastoma; given the paternal phenotype of MTS, the hypothesis of TS in the son is probable.

DISCUSSION

This case suggests that several variants of Lynch syndrome may be seen within the same family. It raises the issue of screening for cerebral tumours in patients with MTS and in their family members, even though such a recommendation does not exist; current recommendations in fact consist primarily of gastrointestinal and gynaecological monitoring.

Turcot syndrome: a synchronous clinical presentation of glioblastoma multiforme and adenocarcinoma of the colon

Turcot syndrome (TS) is a rare hereditary disorder clinically characterized by the occurrence of primary tumors of the colon and the central nervous system (CNS). Here we present the case of an 11-year-old boy with a synchronous clinical presentation of both glioblastoma multiforme (GBM) and colonic adenocarcinoma. A molecular genetic study revealed microsatellite instability in the DNA mismatch repair (MMR) gene. This patient ultimately survived for 13 months after clinical presentation. Based on this case study, the synchronous presentation of glioblastoma multiforme and adenocarcinoma of the colon might suggest a shorter survival rate for patients with Turcot syndrome. A literature review complements this paper.

Café-au-lait spots and early onset colorectal neoplasia: a variant of HNPCC?

BACKGROUND

Café-au-lait spots (CALS) are classically found in neurocutaneous syndromes such as neurofibromatosis, but have not been associated with hereditary colorectal cancer. However, review of hereditary colorectal cancer case reports reveals occasional description of CALS on physical exam.

METHODS

We describe the colonic and extracolonic phenotype in a family with CALS and early onset colorectal neoplasia (adenomas and/or cancer) and review 23 additional families reported in the literature.

RESULTS

Among the 24 families, 32/59 (54.2%) individuals had colorectal adenomas diagnosed at a mean age of 15.7 +/- 1.1 (SE) years (range 5-38 years). The majority (24/32, 75.0%) of persons at first colorectal examination had oligopolyposis (< 100 polyps) versus polyposis (> or = 100 polyps). Forty-two of 59 (71.2%) individuals were affected with colorectal cancer, diagnosed at a mean age of 31.9 +/- 2.7 years (range 5-70 years). A brain tumor was found in 28/59 (47.5%) affected individuals (4 families with 2 or more cases) with an overall mean age of diagnosis of 16.5 +/- 1.2. Lymphoma and/or leukemia was found in 8/24 (33.3%) families (one family with 3 cases). Two families had mutation of the mismatch repair gene, hPMS2 (1 with homozygous germline mutation), while two carried homozygous germline mutations of another mismatch repair gene, hMLH1.

CONCLUSIONS

Café-au-lait spots with early onset colorectal neoplasia may identify families with a variant of HNPCC characterized by oligopolyposis, glioblastoma at young age, and lymphoma. This variant may be caused by homozygous mutation of the mismatch repair genes, such as hPMS2 or hMLH1.

Familial gliomas. Analysis of six families with cerebral gliomas and without other inheritable syndromes

Although a familial tendency to develop brain tumors in the absence of well-recognized hereditary disorders is an important issue, it has been rarely reported. Studies of the familial occurrence of gliomas have yielded conflicting results. This phenomenon may be imputable to chance or environmental or hereditary factors. Furthermore, epidemiological and genetic investigations are fundamental to evidence of whether hereditary factors are active in the development of these tumors. We describe a group of six families, in each of which more than one member had glioma, and discuss the probable mechanisms of oncogenesis in familial tumors in light of the pertinent literature.

Turcot syndrome in an elderly adult

A 67-year-old woman presented with hematochezia and an episode of transient expressive dysphasia. She was found to have multiple colonic polyps with adenocarcinomatous changes. Computed tomography brain scan and computed tomography-guided biopsy revealed a left frontoparietal glioblastoma multiforme. This case illustrates the rare presentation of Turcot syndrome-a hereditary colorectal polyposis syndrome-in an older adult.

Evidence for a recessive inheritance of Turcot's syndrome caused by compound heterozygous mutations within the PMS2 gene

Turcot's syndrome is a genetic disease characterized by the concurrence of primary brain tumors and colon cancers and/or multiple colorectal adenomas. We report a Turcot family with no parental consanguinity, in which two affected sisters, with no history of tumors in their parents, died of a brain tumor and of a colorectal tumor, respectively, at a very early age. The proband had a severe microsatellite instability (MIN) phenotype in both tumor and normal colon mucosa, and mutations in the TGFbeta-RII and APC genes in the colorectal tumor. We identified two germline mutations within the PMS2 gene: a G deletion (1221delG) in exon 11 and a four-base-pair deletion (2361delCTTC) in exon 14, both of which were inherited from the patient's unaffected parents. These results represent the first evidence that two germline frameshift mutations in PMS2, an MMR gene which is only rarely involved in HNPCC, are not pathogenic per se, but become so when occurring together in a compound heterozygote. The compound heterozygosity for two mutations in the PMS2 gene has implications for the role of protein PMS2 in the mismatch repair mechanism, as well as for the presymptomatic molecular diagnosis of at-risk family members. Furthermore, our data support and enlarge the notion that high DNA instability in normal tissues might trigger the development of cancer in this syndrome.

Turcot syndrome with colonic obstruction and small intestinal invagination: report of a case

We report herein the case of a 16-year-old boy diagnosed as having Turcot syndrome, otherwise known as glioma-polyposis syndrome. The patient was transferred from the Department of Neurosurgery where he was undergoing investigation of a brain tumor, to the Department of Medicine for investigation of gastrointestinal symptoms. The patient was diagnosed as having Turcot syndrome, and was then transferred to the Department of Surgery for treatment of an obstruction in the sigmoid colon and small intestinal invagination. A subtotal colectomy with side-to-end ileoproctostomy and release of the invaginations was carried out. Multiple polyps were found in the colon, two of which, including a large polyp that obstructed the colonic lumen, were confirmed histologically to be adenocarcinoma. The remaining polyps were adenomas. A biopsy of the brain tumor confirmed a diagnosis of astrocytoma (WHO grade II). This case report describes the characteristic features of Turcot syndrome presented by this patient.

The hPMS2 exon 5 mutation and malignant glioma. Case report

Patients with Turcot syndrome (TS) are predisposed to colon tumors and primary brain tumors, typically glioblastomas or medulloblastomas. The authors describe a patient with TS featuring a known germline mutation of exon 5 of the hPMS2 mismatch repair gene who developed two metachronous glioblastomas, both with distinct oligodendroglial features. Molecular genetic analysis revealed allelic loss of chromosome 19q in the patient's second tumor but no allelic loss of chromosome 1p. Prominent microsatellite instability was also found in this tumor, consistent with a germline mismatch repair defect. Because this patient had an unusual underlying condition and his tumor had a unique histological appearance for TS, it was hypothesized that this genetic defect may predispose to malignant gliomas with oligodendroglial features. The authors therefore evaluated whether sporadic glioblastomas and oligodendrogliomas undergo mutations of this region of the hPMS2 gene. However, single-strand conformation polymorphism analysis of hPMS2 exon 5 failed to reveal mutations in 20 sporadic glioblastomas and 16 sporadic oligodendroglial gliomas. Thus, although it is possible that the germline hPMS2 exon 5 mutation may predispose to glioblastomas with an oligodendroglial component, the same genetic defect is not commonly involved in sporadic oligodendrogliomas or glioblastomas.

A father and son with Turcot's syndrome: evidence for autosomal dominant inheritance: report of two cases

Typical Turcot's syndrome is characterized by the association of a brain glioma together with multiple colonic polyposis, in which the number of polypoid lesions is small and the association of colonic cancer occurs at a younger age than in familial adenomatous polyposis. We describe a family in which both the father and his son presented with typical Turcot's syndrome without parental consanguinity. This is the first report of a family that is considered to follow an autosomal dominant inheritance. After reviewing 25 documented cases in which the average age of death was 20.3 years old, it was learned that the major cause of death was brain tumor (76 percent) and the minor cause was colon cancer (16 percent). Patients were very young and, therefore, unlikely to have produced a child before their death. These facts seem to support the theory that Turcot's syndrome is an autosomal dominant disorder.

Case report: an inherited APC mutation in the first reported Australian case of Turcot's syndrome

The objective of this study was to determine the inherited gene mutation responsible for the first reported Australian case of Turcot's syndrome. DNA was extracted from the archival tissue blocks obtained at the time of the patient's original surgery and from fresh blood samples obtained from selected family members. These were analysed for mutations of the familial adenomatous polyposis gene (APC). Analysis of DNA from the archival blocks and from each of the affected family members revealed an inherited 5 base pair deletion at codon 1061 of APC. In this case, the central nervous system tumour represents an extracolonic manifestation of familial adenomatous polyposis. The underlying inherited mutation of APC has been identified. In some cases of Turcot's syndrome, other genes appear to be involved. Recent literature examining the molecular basis of Turcot's syndrome is reviewed.

Molecular analysis of the APC gene in 105 Dutch kindreds with familial adenomatous polyposis: 67 germline mutations identified by DGGE, PTT, and southern analysis

Germline mutations of the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis (FAP), an autosomal dominant predisposition to colorectal cancer. We screened the entire coding region of the APC gene for mutations in an unselected series of 105 Dutch FAP kindreds. For the analysis of exons 1-14, we employed the GC-clamped denaturing gradient gel electrophoresis (DGGE), while the large exon 15 was examined using the protein truncation test. Using this approach, we identified 65 pathogenic mutations in the above 105 apparently unrelated FAP families. The mutations were predominantly either frameshifts (39/65) or single base substitutions (18/65), resulting in premature stop codons. Mutations that would predict abnormal RNA splicing were identified in seven cases. In one of the families, a nonconservative amino acid change was found to segregate with the disease. In spite of the large number of APC mutations reported to date, we identified 27 novel germline mutations in our patients, which reiterates the great heterogeneity of the mutation spectrum in FAP. In addition to the point mutations identified in our patients, structural rearrangements of APC were found in two pedigrees, by Southern blot analysis. The present study indicates that the combined use of DGGE, protein truncation test, and Southern blot analysis offers an efficient strategy for the presymptomatic diagnosis of FAP by direct mutation detection. We found that the combined use of the currently available molecular approaches still fails to identify the underlying genetic defect in a significant subset of the FAP families. The possible causes for this limitation are discussed.

Polyposis coli, craniofacial exostosis and astrocytoma: the concomitant occurrence of the Gardner's and Turcot syndromes

BACKGROUND

Up to 60% of the patients with known adenomatous polyposis coli may present hyperostosis of the skull and facial bones, and/or a susceptibility to fibromas. This is known as the Gardner's syndrome, and is considered as an allelic variant of familial adenomatous polyposis (FAP). Also, although very rare, an adenomatous polyposis coli may occur with malignant tumors of the central nervous system, known as Turcot syndrome. If both syndromes are different phenotypic presentation of FAP, this would explain a simultaneous occurrence.

METHOD

We report the history of a patient who showed clinical signs of the simultaneous occurrence of both Gardner's and Turcot syndromes. The syndromes are compared, and in view of the literature, a genetic explanation for the concomitant occurrence is discussed.

RESULTS

Evidence obtained from the literature to consider Turcot syndrome as a phenotype of FAB is as follows: (1) The occurrence of Gardner's and Turcot syndromes in one family, but in different members; (2) The presence of congenital hypertrophic retinal pigmented epithelium (CHRPE), which correlates with the expression of polyps in FAP patients, in both syndromes; (3) Linkage of the Turcot phenotype to the adenomatous polyposis coli locus by genetic markers. Evidence obtained from this case report indicates that there is a manifestation of both syndromes in one patient together with a positive family history for FAP.

CONCLUSION

This concomitant occurrence of both Gardner's and Turcot syndromes in one patient clinically supports genetic and ophthalmic investigation to consider Turcot syndrome (like Gardner's syndrome) as a phenotypic variant of FAP. Patients with FAP should be examined for the presence of Gardner's syndrome. In case a Gardner's syndrome is suspected, a computed tomography scan of the brain is recommended because of the possible existence of a simultaneous Turcot syndrome.

Triple primary malignant neoplasms including a malignant brain tumor: report of two cases and review of the literature

BACKGROUND

Two rare cases of triple primary malignant neoplasms (PMN), including malignant brain tumors, which were glioblastoma multiformes, are described.

METHODS

The clinical characteristics and underlying genetic alterations in triple or more PMN, including malignant brain tumors are discussed with intensive review of the literature.

RESULTS

The first patient, a 77-year-old male, suffered metachronously from tubular adenocarcinoma of the stomach, transitional cell carcinoma of the bladder, and glioblastoma in the brain. This glioblastoma had loss of heterozygosity in exons 7-8 in p53 gene. The second patient, a 68-year-old male, developed papillary adenocarcinoma of the lung, adenocarcinoma of the rectum, and glioblastoma in the brain during a period of 7 years. In 42 such cases described in the literature, age distribution demonstrated two characteristic peaks, one in the third decade and the other over 50 years of age. The younger group consisted mainly of Turcot's syndrome, and of a case of Li-Fraumeni familial cancer syndrome. On the other hand, neither of these hereditary cancer syndromes were contained in the elder group. Regarding the site of PMN, colorectal cancers were associated most frequently with malignant brain tumors, followed by stomach cancers, and thyroid cancers. Malignant brain tumors, mostly glioblastoma multiforme, tend to occur as the last tumor of triple or more PMN.

CONCLUSIONS

These results suggest that genetic background might play an important role in tumorigenesis of PMN in the younger group, whereas epigenetic factors would be more important in the older group. Characteristic organ association and factors influencing carcinogenesis, such as aging, environmental carcinogens, and underlying genetic alterations in these tumors are further discussed.

Familial adenomatous polyposis: a submicroscopic deletion at the APC locus in a family with mentally normal patients

Cytogenetically visible deletions that include the adenomatosis polyposis coli (APC) locus have repeatedly been reported in mentally handicapped polyposis patients. We report on a family with a submicroscopic deletion of about 200 kb including more than the 3' half of the APC gene and the adjacent DP1 gene. The deletion was detected by linkage analysis with flanking and intragenic markers and proven by in situ hybridisation with intragenic cosmid clones. All the familial adenomatous polyposis (FAP) patients and persons at risk in the family show normal behaviour and intelligence. Thus, it is conceivable that at least some of the FAP patients in whom mutations could not be identified by routine methods may have large but submicroscopic deletions.

Hereditary tumor syndromes of the nervous system: overview and rare syndromes

Hereditary tumor syndromes of the nervous system are a varied group of conditions that include neurofibromatosis 1, neurofibromatosis 2, tuberous sclerosis, and von Hippel-Lindau disease, as well as the retinoblastoma susceptibility, Li-Fraumeni, familial glioma, Turcot, Gorlin, Cowden and multiple endocrine neoplasia syndromes. For many of these conditions, the responsible genes have been localized or identified. Such studies have elucidated the genetic basis of both hereditary cancer predisposition and sporadic nervous system tumors. The first four hereditary tumors syndromes have been extensively studied and are discussed in detail in the four subsequent articles. The other syndromes have also been subject to both pathological and molecular genetic inquiries. In this introductory overview, we discuss the features common to the hereditary tumor syndromes of the nervous system, and review some of the rarer conditions.

The molecular basis of Turcot's syndrome

BACKGROUND

Turcot's syndrome is characterized clinically by the concurrence of a primary brain tumor and multiple colorectal adenomas. We attempted to define the syndrome at the molecular level.

METHODS

Fourteen families with Turcot's syndrome identified in two registries and the family originally described by Turcot and colleagues were studied. Germ-line mutations in the adenomatous polyposis coli (APC) gene characteristic of familial adenomatous polyposis were evaluated, as well as DNA replication errors and germline mutations in nucleotide mismatch-repair genes characteristic of hereditary nonpolyposis colorectal cancer. In addition, a formal risk analysis for brain tumors in familial adenomatous polyposis was performed with a registry data base.

RESULTS

Genetic abnormalities were identified in 13 of the 14 registry families. Germ-line APC mutations were detected in 10. The predominant brain tumor in these 10 families was medulloblastoma (11 of 14 patients, or 79 percent), and the relative risk of cerebellar medulloblastoma in patients with familial adenomatous polyposis was 92 times that in the general population (95 percent confidence interval, 29 to 269; P < 0.001). In contrast, the type of brain tumor in the other four families was glioblastoma multiforme. The glioblastomas and colorectal tumors in three of these families and in the original family studied by Turcot had replication errors characteristic of hereditary nonpolyposis colorectal cancer. In addition, germ-line mutations in the mismatch-repair genes hMLH1 or hPMS2 were found in two families.

CONCLUSIONS

The association between brain tumors and multiple colorectal adenomas can result from two distinct types of germ-line defects: mutation of the APC gene or mutation of a mismatch-repair gene. Molecular diagnosis may contribute to the appropriate care of affected patients.

Turcot's syndrome: case report and review of the classification

We report a case of association of a brain tumor with multiple colorectal polyposis and offer an analysis of the relevant literature with a view to revising the classification of the syndrome in relation to familial multiple polyposis and Gardner's syndrome. Differences emerged, depending on the brain tumor type, which suggests that this association may be classified as two distinct syndromes.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant condition resulting in the development of more than 100 adenomatous polyps in the large bowel. In addition, a number of extracolonic manifestations of the condition may occur. Recently, increasing knowledge relating to the extracolonic abnormalities, and localization and sequencing of the gene for FAP, have had important implications for screening and long-term follow-up of those affected. In this review the natural history of the disease and the extracolonic manifestations associated with it are considered. Surgical management and advances in understanding at a molecular level are discussed, as well as the problems relating to screening for FAP and the implications of the new knowledge.

Germ-line and somatic mutations of the APC gene in patients with Turcot syndrome and analysis of APC mutations in brain tumors

The Turcot syndrome (TS) is a rare, probably autosomal recessive, disorder characterized by development of primary neuroepithelial tumors of the central nervous system (CNS) and numerous adenomatous colorectal polyps. To examine the possible involvement of mutations of the APC gene, which is responsible for familial adenomatous polyposis (FAP), in Turcot syndrome, we examined DNAs from TS patients for alterations in this gene by means of ribonuclease protection analysis. Germ-line APC mutations were detected in each of three unrelated cases of TS, and additional (somatic) mutations were observed in colonic adenomas that had developed in one of these patients. However, no somatic mutations in APC were found among 91 neuroepithelial tumors (medulloblastoma, glioblastoma, astrocytoma, and oligodendroglioma), whether sporadic or associated with TS. These results suggest that the APC gene is associated with pathogenesis of one feature of TS, but that at least one other gene is responsible for the genesis of neuroepithelial tumors in the CNS.

Genetics of primary brain tumors: a review

In this review we provide evidence for the existence of genes associated with primary malignant brain tumors. We summarize the current knowledge from studies of familial cancer aggregation, hereditary syndromes, and molecular and cytogenetic studies. The epidemiologic evidence is suggestive but inconclusive for an association between brain tumors and cancers in other family members, including cancers of the breast, lung and colon. Central nervous system (CNS) tumors have been associated with several hereditary syndromes including the Li-Fraumeni cancer family syndrome, neurofibromatosis (types 1 and 2), tuberous sclerosis, nevoid basal cell carcinoma syndrome, familial polyposis, and von Hippel-Lindau disease. Significant studies leading to the recognition of molecular and cytogenetic abnormalities in malignant gliomas are described in detail. The genetic studies conducted thus far suggest a role for inherited susceptibility in some CNS tumors.

Evolution of hereditary bowel cancer

Familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) are both inherited as autosomal dominant conditions in which the mutation gives rise to a tendency to produce precancerous adenomas. However these two forms of hereditary bowel cancer show important differences at the clinical, pathological and molecular genetic levels. It is argued that the first tissue manifestation of FAP is the unicryptal adenoma. The existence of a preceding field change characterised by diffuse hyperproliferation and various altered phenotypes does not stand up to critical scrutiny. The processes of neoplastic evolution in FAP and HNPCC are compared in detail. It is suggested that an understanding of the function of the FAP and HNPCC genes will lead to the development of cancer prevention strategies aimed at blocking the earliest stages of neoplastic development.

Non-allelic heterogeneity of familial adenomatous polyposis

Linkage studies on familial adenomatous polyposis (FAP) reported so far suggest that FAP is a genetically homogeneous disease. Recently, we found that the putative gene for Turcot syndrome, an apparently autosomal recessive clinical variant of FAP, is not allelic to FAP. Here we describe another family, segregating for an autosomal dominant disease clinically indistinguishable from FAP but genetically not linked to the APC locus, adding further evidence for the occurrence of non-allelic heterogeneity of FAP. These observations have implications to the linkage-based genetic counselling of persons at risk for FAP especially when they are drawn from small families giving insufficient information.

Turcot's syndrome and familial adenomatous polyposis associated with brain tumor: review of related literature

We investigated clinical manifestations in 124 patients with a possible Turcot's syndrome whose data were taken from documented cases. The cases were subclassified mainly on the bases of the type of familial occurrence and listed in five Tables. We searched for differences in colonic manifestation, histologic type of glioma, mode of inheritance, frequency of parental consanguinity, skin lesions and other accompanying lesions among these five groups. The differences of these clinical findings suggested that glioma-polyposis syndrome should be classified as follows; (1) cases of Turcot's syndrome who had characteristic colonic and brain manifestations, (2) cases of FAP associated with glioma, (3) suspicious cases of glioma-polyposis, and (4) cases other than glioma-polyposis syndrome.