Matthias Jungck

Muir-Torre Phenotype Has a Frequency of DNA Mismatch-Repair-Gene Mutations Similar to That in Hereditary Nonpolyposis Colorectal Cancer Families Defined by the Amsterdam Criteria

Muir-Torre syndrome (MTS) is an autosomal dominant disease defined by the coincidence of at least one sebaceous skin tumor and one internal malignancy. About half of MTS patients are affected by colorectal cancer. In a subgroup of MTS patients the disease has an underlying DNA mismatch-repair (MMR) defect and thus is allelic to hereditary nonpolyposis colorectal cancer (HNPCC). The purpose of this study was to examine to what extent germ-line mutations in DNA MMR genes are the underlying cause of the MTS phenotype. We ascertained 16 MTS patients with sebaceous skin tumors and colorectal cancer, and we examined their skin and visceral tumors for microsatellite instability. All the patients exhibited high genomic instability in at least one tumor. The search for germ-line mutations in the hMSH2 and hMLH1 genes in 13 of the MTS patients revealed truncating mutations in 9 (69%): eight mutations in the hMSH2 gene and one in the hMLH1 gene. This is the first systematic search for germ-line mutations in patients ascertained on the basis of sebaceous skin tumors. Our results indicate that (1) MTS patients exhibit significantly more mutations in the hMSH2 gene than in the hMLH1 gene; and (2) the subpopulation of MTS patients who are also affected by colorectal cancer, irrespective of family history and age at onset of tumors, may have a likelihood for an underlying DNA MMR defect similar to that for patients with a family history fulfilling the strict clinical criteria for HNPCC.

Hereditary nonpolyposis colorectal cancer: frequent occurrence of large genomic deletions in MSH2 and MLH1 genes.

Hereditary nonpolyposis colorectal cancer (HNPCC) is often caused by a deficiency in DNA mismatch repair. By using conventional methods of mutation analysis, point mutations in the DNA mismatch repair genes MSH2 and MLH1 have been detected in up to 64% of patients suspected of HNPCC. However, large genomic deletions cannot be detected by these methods. In our study, we applied a semiquantitative multiplex PCR to detect the proportion of large deletions in patients meeting the Bethesda criteria whose tumours exhibited microsatellite instability (MSI). Of 368 unrelated patients, 180 exhibited MSI. In these patients, 68 disease‐causing point mutations (38%) had previously been detected in the MSH2 and MLH1 genes by SSCP, heteroduplex analysis or DHPLC followed by direct sequencing. The remaining 112 patients (including 24 patients with rare missense or other unclarified variants) were examined for large deletions. We identified deletions in 19 patients (10.6%); 11/19 (58%) deletions were located in MSH2 and 8/19 (42%) in MLH1, respectively. The size of deletions ranged from 1 exon to a deletion of a whole gene. Five breakpoints of deletions were sequenced; Alu‐repetitive elements were involved in all of them. In patients meeting the Amsterdam criteria the proportion of large deletions was 12.6%. A similar proportion of deletions was found in the group of patients with a positive family history for colorectal cancer and MSI tumours, not meeting the Amsterdam criteria. The results of our study suggest that large genomic deletions in both MSH2 and MLH1 genes play a considerable role in the pathogenesis of HNPCC and should be part of the routine HNPCC mutation detection protocols.

Frequent 4-bp deletion in exon 9 of the SMAD4/MADH4 gene in familial juvenile polyposis patients

Familial juvenile polyposis (FJP) is a hamartomatous polyposis syndrome characterized by the appearance of juvenile polyps in the gastrointestinal tract. Patients with this syndrome are at an increased risk for cancer of the colon, stomach, and pancreas. Recently, germline mutations in the SMAD4/DPC4 gene (official symbol MADH4) have been found in the majority of patients suffering from FJP. We have examined 11 unrelated patients with FJP for MADH4 germline mutations by direct sequencing of genomic DNA encompassing all 11 exons of the gene. Besides a novel mutation (959–960delAC at codon 277, exon 6) in one patient, we observed a 4‐bp deletion (1372–1375delACAG) in exon 9 in two unrelated patients. Examination with microsatellite markers flanking MADH4 supports an independent origin of the mutation in these two families. The same 4‐bp deletion in exon 9 has previously been described in three out of nine patients examined for MADH4 mutations. Our results combined with these previous data demonstrate that a unique 4‐bp deletion in exon 9 of MADH4 accounts for about 25% of all FJP cases and that other MADH4 mutations occur in an additional 15% of patients. Genes Chromosomes Cancer 25:403–406, 1999.

Frequency of Hereditary Non-Polyposis Colorectal Cancer among Unselected Patients with Colorectal Cancer in Germany

Introduction: Hereditary non-polyposis colorectal cancer (HNPCC) is a major form of familial colorectal cancer (CRC). It is diagnosed when either the Amsterdam criteria (AC) are fulfilled or mutations in one of the mismatch repair (MMR) genes have been identified. This project aims at estimating the proportion of HNPCC among unselected patients with CRC. Patients and Methods: During a period of 2 years, a total of 351 non-selected patients with CRC were registered prospectively. 92 patients met the Bethesda criteria (9 of them fulfilled the AC) and 259 did not. 348 tumours were examined for microsatellite instability (MSI) and expression of MMR proteins. Results: MSI-H and MSI-L were identified in 17 and 6%, respectively. Loss of MSH2 or MLH1 was found in 1.5 and 8.8%, respectively. Based on the results of tumour tissue analyses, 80 patients with MSI and/or loss of MSH2 or MLH1 expression were identified as candidates for germline mutation screening. DNA of 40/80 patients was available. These patients were screened for MSH2 and MLH1 mutations; 19/40 patients with MSI and normal MSH2 or MLH1 expression were screened for mutations in MSH6. Three patients had relevant MMR gene mutations and six variants of unknown functional relevance were detected. Conclusions: After adjusting for the cases not evaluable for germline mutations, 1.7% of the CRC patients had HNPCC proven by molecular genetics.

Arylamine N-acetyltransferase type 2 and glutathione S-transferases M1 and T1 polymorphisms in familial adenomatous polyposis

Familial adenomatous polyposis (FAP) exhibits a variable phenotype even in carriers of the same adenomatous polyposis coli germline mutation. Xenobiotic-metabolizing enzymes such as N-acetyltransferases (NATs) and glutathione S-transferases (GSTs) were reported to modify the individual risk for colorectal cancer. We examined whether the polymorphisms of the NAT2, GSTM1, and GSTT1 enzymes affect age at diagnosis of first colorectal adenomas or extracolonic manifestations in 411 FAP patients. Neither age at diagnosis of colorectal adenomas nor occurrence of extra-intestinal tumors differed significantly between genotypes at the NAT2 and GSTM1 loci, whereas GSTT1 polymorphism showed an uncertain association with extra-intestinal manifestations. Combinations of supposed at risk genotypes of the three enzymes showed no significant differences either. Thus, NAT2, GSTM1, or GSTT1 are unlikely to modify the disease phenotype in FAP patients.

ERBLICH BEDINGTE GASTROINTESTINALE TUMORERKRANKUNGEN

Zum ThemaDie kolorektalen Karzinome zählen zu den am besten untersuchten Tumoren, da sie vom frühen Adenom bis zum metastasierenden Karzinom endoskopischer Untersuchung und besser zugänglich sind als andere solide Tumoren.Die erbliche Disposition beruht auf der Annahme, daß autosomal codierende Gene in jeweils 2 Allelen vorhanden sind. Über die Keimbahn vererbte Veränderungen in Tumorsuppressor-Genen eines Allels werden zunächst durch das zweite Allel kompensiert. Fällt auch dieses aus, z.B. durch eine somatische Mutation, resultiert ein Funktionsausfall und somit unkontrolliertes Zellwachstum und Tumorentstehung.Auch andere molekulare Mechanismen spielen eine wichtige Rolle bei der gastrointestinalen Tumorgenese, da Magen- und Darmschleimhaut eine sehr hohe Zellproliferation haben und somit leichter Störungen im Zellgleichgewicht zwischen Proliferation und programmiertem Zelltod (Apoptose) auftreten können.In dieser Arbeit über genetisch bedingte gastrointestinale Tumorerkrankungen werden die familiäre adenomatöse Polyposis (FAP), das autosomal-dominante erbliche nicht polypöse Kolonkarzinom (HNCPP), die hamartomatösen Polyposen (Peutz-Jeghers-Syndrom, familiäre juvenile Polyposis, Cowden-Syndrom) und das familiäre Magenkarzinom behandelt.

Humangenetische Beratung bei erblichen Tumordispositionserkrankungen

Unsere Kenntnisse uber die molekularen Ablaufe bei der Tumorentstehung und -progression haben sich in den letzten 10 Jahren dramat isch verbessert. Die Moglichkeiten der molekulargenetischen Diagnostik sind dadurch ebenfalls dramat isch gewachsen. Dies gilt u.a. auch fur viele haufige Krebserkrankungen, wie z.B. das Mammakarzi nom oder das kolorektale Karzinom. Von diesen konnten erbliche Unterformen abgegrenzt werden, die einem autosomal-dominanten Erbgang folgen. Umfragen haben gezeigt, dass in der Bevolkerung ein groBes Interesse am Screening auf Krebserkrankungsrisiken besteht (Andrykowski et al. 1997), leider ist jedoch das Wissen uber die Aussagekraft von solchen Untersuchungen selbst unter Arzten oft mangelhaft (Giardiello et al. 1997). Neben dem groBen moglichen Adressatenkrei s und den Schwierigkeiten bei der Interpretation der Ergebnisse wiegt aber noch viel schwerer, dass die Aussage, die am Ende einer Diagnostik bei erblichen Tumordispositionserkrankungen stehen kann, eine vollig neue Dimension in der Medizin darstellt.

Die genetischen Grundlagen erblicher Tumorkrankheiten des Menschen

Für nahezu alle Krebserkrankungen gilt, daß jeweils ein relativ geringer Anteil auf einer erblichen Tumordisposition beruht. Einerseits erlaubt die Kenntnis der krankheitsverursachenden Gene in vielen Fällen, durch die genaue Charakterisierung der Mutation bei einem Betroffenen die Erblichkeit der Erkrankung zu beweisen. Andererseits ergibt sich hierdurch die grundsätzliche Möglichkeit – und das ist viel wichtiger – bei nicht erkrankten Blutsverwandten dieses Patienten festzustellen, ob sie die Mutation ebenfalls geerbt haben und damit mit hoher Wahrscheinlichkeit an einem Tumor erkranken werden.

Peutz-Jeghers syndrome: four novel inactivating germline mutations in the STK11 gene. Mutations in brief no. 227. Online.

In order to obtain a survey of the mutations being prevalent in Northern Germany and to enable molecular genetic testing for families with clinically diagnosed familial hypercholesterolemia (FH), we screened 46 unrelated German individuals with elevated LDL levels for mutations in the 18 exons and their flanking intron sequences including the promotor region of the LDL receptor (LDLR) gene. In addition, we tested all patients for the presence of mutations in the gene coding for apolipoprotein B-100 (apoB-100). We detected 15 mutations affecting the LDLR gene, 8 of which, designated A29S, 195insAT, 313+1insG, 553insG, 680insGGACAAATCTG, D200N, E267K and L411V have not yet been reported. One patient is heterozygous for the double mutant N543H and 2393del9Bp. Two patients carried the mutation R3500Q (Arg-->Glu) within the apoB-100 gene.The diagnosis of Peutz‐Jeghers syndrome is based on the occurrence of hamartomatous gastrointestinal polyps and perioral pigment spots. In view of the development of hamartomatous polyps in several syndromes and the variability of pigment spots in Peutz‐Jeghers patients, identification of affected individuals is difficult. Recently, germline mutations in the STK11 gene have been reported as a molecular cause of Peutz‐Jeghers syndrome. We present four novel inactivating mutations identified by direct sequencing of all 9 exons of the STK11 gene in 4 patients suggestive of Peutz‐Jeghers syndrome: three frameshift mutations (125‐137del; 474‐480del; 516‐517insT) and one nonsense mutation (Q220X). Our data obtained in these patients and in those reported previously emphasize the diagnostic value of histological discrimination between different types of hamartomatous polyps and of molecular analysis, particularly in cases with no family history of the disease.