Mutations in DNA MMR genes, mainly MSH2 and MLH1, account for the majority of HNPCC, an autosomal dominant predisposition to colorectal cancer and other malignancies. The evaluation of many questions regarding HNPCC requires clinically and genetically well-characterized HNPCC patient cohorts of reasonable size. One main focus of this multicenter study is the evaluation of the mutation spectrum and mutation frequencies in a large HNPCC cohort in Germany; 1,721 unrelated patients, mainly of German descent, who met the Bethesda criteria were included in the study. In tumor samples of 1,377 patients, microsatellite analysis was successfully performed and the results were applied to select patients eligible for mutation analysis. In the patients meeting the strict Amsterdam criteria (AC) for HNPCC, 72% of the tumors exhibited high microsatellite instability (MSI-H) while only 37% of the tumors from patients fulfilling the less stringent criteria showed MSI-H; 454 index patients (406 MSI-H and 48 meeting the AC of whom no tumor samples were available) were screened for small mutations. In 134 index patients, a pathogenic MSH2 mutation, and in 118 patients, a pathogenic MLH1 mutation was identified (overall detection rate for pathogenic mutations 56%). One hundred sixty distinct mutations were detected, of which 86 are novel mutations. Noteworthy is that 2 mutations were over-represented in our patient series: MSH2,c.942+3A>T and MLH1,c.1489_1490insC, which account for 11% and 18% of the MSH2 and MLH1 mutations, respectively. A subset of 238 patients was screened for large genomic deletions. In 24 (10%) patients, a deletion was found. In 72 patients, only unspecified variants were found. Our findings demonstrate that preselection by microsatellite analysis substantially raises mutation detection rates in patients not meeting the AC. As a mutation detection strategy for German HNPCC patients, we recommend to start with screening for large genomic deletions and to continue by screening for common mutations in exon 5 of MSH2 and exon 13 of MLH1 before searching for small mutations in the remaining exons. ' 2005 Wiley-Liss, Inc.

No abstract

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder that predisposes to predominantly colorectal and endometrial cancers due to germline mutations in DNA mismatch repair genes, mainly MLH1, MSH2 and in families with excess endometrial cancer also MSH6. In this population-based study, we analysed the mutation spectrum of the MLH1, MSH2 and MSH6 genes in a cohort of patients with microsatellite unstable double primary tumours of the colorectum and the endometrium by PCR, DHPLC and sequencing. nl).A germline mutation in one of the MMR genes in HNPCC patients predisposes to an early onset colon cancer: 30% risk to age 40 and over 80% lifetime risk, 9 compared to 3-4% in the general population. In addition, affected individuals are prone to develop multiple primary cancers, both from the colorectum and extracolonic sites, of which endometrial cancers are the most common with a lifetime risk of 20 -43% in women, 10 followed by carcinoma of the ovary, stomach, small intestine and upper urinary tract. 11 When the MMR system is defective, especially when due to MLH1 and MSH2 mutations, replication errors arising during DNA replication are not corrected, which results in widespread genomic instability. Through their repetitive nature, microsatellites are particularly prone to replication errors and therefore microsatellite instability (MSI) is a hallmark of MMR deficiency. MSI is found in more than 90% of all HNPCC tumours 12 but only in 10 -15% of sporadic colorectal tumours. 13 Moreover, MMR deficiency leads to an increased mutation rate in specific cancer related genes, including BAX, 14 IGFIIR 15 and TGF-␤ type II receptor, 16 which may enhance tumour progression. While MLH1 and MSH2 defects give instability primarily in dinucleotide repeats, 13 MSH6-defective tumours show alterations in predominantly mononucleotide repeats. [17][18][19] This is in congruence with the biological function, where MLH1 and MSH2 manage repair of small insertion/deletion loops, 20,21 while MSH6 mostly is involved in repair of base-base and single nucleotide insertion/deletion mismatches. 22,23 Double primary cancers within the HNPCC spectrum is a hallmark of HNPCC and an indicator to clinically suspect HNPCC. 24 In a previous population-based study, 25 we observed an increased risk of HNPCC-associated cancers in first-degree relatives to patients diagnosed with double primary cancers of the colorectum or the colorectum/endometrium. The overall standardised incidence ratio (SIR) was 1.69 (95% CI; 1.39 -2.03). The SIR was highest among relatives to the patients with young age of onset (Ͻ50 years) and MSI positive tumours. The aim of our study was to investigate the MLH1, MSH2 and MSH6 mutation spectrum in the patients with MSI positive double primary tumours. MATERIAL AND METHODS PatientsSeventy-eight patients with double primary cancers of the colorectum or the colorectum and the endometrium (Fig. 1) were identified in a population-based cohort study previously reported. 25 The MSI status of one of the patie...

Background: Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder predisposing to predominantly colorectal cancer (CRC) and endometrial cancer frequently due to germline mutations in DNA mismatch repair (MMR) genes, mainly MLH1, MSH2 and also MSH6 in families seen to demonstrate an excess of endometrial cancer. As a consequence, tumors in HNPCC reveal alterations in the length of simple repetitive genomic sequences like poly-A, poly-T, CA or GT repeats (microsatellites) in at least 90% of the cases. Aim of the Study: The study cohort consisted of 25 HNPCC index patients (19 Amsterdam positive, 6 Bethesda positive) who revealed a microsatellite stable (MSS) – or low instable (MSI-L) – tumor phenotype with negative mutation analysis for the MMR genes MLH1 and MSH2. An extended marker panel (BAT40, D10S197, D13S153, D18S58, MYCL1) was analyzed for the tumors of these patients with regard to three aspects. First, to reconfirm the MSI-L phenotype found by the standard panel; second, to find minor MSIs which might point towards an MSH6 mutation, and third, to reconfirm the MSS status of hereditary tumors. The reconfirmation of the MSS status of tumors not caused by mutations in the MMR genes should allow one to define another entity of hereditary CRC. Their clinical features were compared with those of 150 patients with sporadic CRCs. Results: In this way, 17 MSS and 8 MSI-L tumors were reclassified as 5 MSS, 18 MSI-L and even 2 MSI-H (high instability) tumors, the last being seen to demonstrate at least 4 instable markers out of 10. Among all family members, 87 malignancies were documented. The mean age of onset for CRCs was the lowest in the MSI-H-phenotyped patients with 40.5 ± 4.9 years (vs. 47.0 ± 14.6 and 49.8 ± 11.9 years in MSI-L- and MSS-phenotyped patients, respectively). The percentage of CRC was the highest in families with MSS-phenotyped tumors (88%), followed by MSI-L-phenotyped (78%) and then by MSI-H-phenotyped (67%) tumors. MSS tumors were preferentially localized in the distal colon supposing a similar biologic behavior like sporadic CRC. MSH6 mutation analysis for the MSI-L and MSI-H patients revealed one truncating mutation for a patient initially with an MSS tumor, which was reclassified as MSI-L by analyzing the extended marker panel. Conclusion: Extended microsatellite analysis serves to evaluate the sensitivity of the reference panel for HNPCC detection and permits phenotype confirmation or upgrading. Additionally, it confirms the MSS status of hereditary CRCs not caused by the common mutations in the MMR genes and provides hints to another entity of hereditary CRC.

No abstract