Evidence for breast cancer as an integral part of Lynch syndrome.

Lynch syndrome, an autosomal dominant cancer predisposition caused by mutations in DNA mismatch repair (MMR) genes, mainly mainly mutL homolog 1, OMIM 120436 (MLH1) and mutS homolog 2, OMIM 609309 (MSH2), encompasses a tumor spectrum including primarily gastrointestinal, endometrial, and ovarian cancer. This study aimed at clarifying the heavily debated issue of breast cancer being part of Lynch syndrome. Detailed clinical data on cancer occurrence in Swiss female MLH1/MSH2 mutation carriers were gathered, all available breast cancer specimens assessed for molecular evidence for MMR deficiency (i.e., microsatellite instability (MSI), MMR protein expression, and somatic (epi)genetic MMR gene alterations) and compiled with the scarce molecular data available from the literature. Seventy unrelated Swiss Lynch syndrome families were investigated comprising 632 female family members at risk of which 92 were genetically verified mutation carriers (52 MLH1 and 40 MSH2). On contrast to endometrial and ovarian cancer, which occurred significantly more often and at younger age in MLH1/MSH2 mutation carriers (median 50.5 and 49.0 years; P < 0.00001), overall cumulative breast cancer incidence closely mirrored the one in the Swiss population (56.5 years). Six (85.7%) of seven breast cancer specimens available for molecular investigations displayed the hallmarks of MMR deficiency. Combined with data from the literature, MSI was present in 26 (70.3%) of 37 and altered MMR protein expression in 16 (72.7%) of 22 breast cancer specimens from MLH1/MSH2 mutation carriers. These findings, thus, provide strong molecular evidence for a pivotal role of MMR deficiency in breast cancer development in Lynch syndrome.

Familial colorectal cancer: eleven years of data from a registry program in Switzerland.

Deleterious germ-line variants involving the DNA mismatch repair (MMR) genes have been identified as the cause of the hereditary nonpolyposis colorectal cancer syndrome known as the Lynch syndrome, but in numerous familial clusters of colon cancer, the cause remains obscure. We analyzed data for 235 German-speaking Swiss families with nonpolyposis forms of colorectal cancer (one of the largest and most ethnically homogeneous cohorts of its kind) to identify the phenotypic features of forms that cannot be explained by MMR deficiency. Based on the results of microsatellite instability analysis and immunostaining of proband tumor samples, the kindreds were classified as MMR-proficient (n = 134, 57%) or MMR-deficient (n = 101, 43%). In 81 of the latter kindreds, deleterious germ-line MMR-gene variants have already been found (62 different variants, including 13 that have not been previously reported), confirming the diagnosis of Lynch syndrome. Compared with MMR-deficient kindreds, the 134 who were MMR proficient were less likely to meet the Amsterdam Criteria II regarding autosomal dominant transmission. They also had primary cancers with later onset and colon-segment distribution patterns resembling those of sporadic colorectal cancers, and they had lower frequencies of metachronous colorectal cancers and extracolonic cancers in general. Although the predisposition to colorectal cancer in these kindreds is probably etiologically heterogeneous, we were unable to identify distinct phenotypic subgroups solely on the basis of the clinical data collected in this study. Further insight, however, is expected to emerge from the molecular characterization of their tumors.

Report of an international survey of molecular genetic testing laboratories.

OBJECTIVE: To collect data on the practices of molecular genetic testing (MGT) laboratories for the development of national and international policies for quality assurance (QA). METHODS: A web-based survey of MGT laboratory directors (n = 827; response rate 63%) in 18 countries on 3 continents. QA and reporting indices were developed and calculated for each responding laboratory. RESULTS: Laboratory setting varied among and within countries, as did qualifications of the directors. Respondents in every country indicated that their laboratory receives specimens from outside their national borders (64%, n = 529). Pair-wise comparisons of the QA index revealed a significant association with the director having formal training in molecular genetics (p < 0.005), affiliation with a genetics unit (p = 0.003), accreditation of the laboratory (p < 0.005) and participation in proficiency testing (p < 0.005). Research labs had a lower mean report score compared to all other settings (p < 0.05) as did laboratories accessioning <150 samples per year. CONCLUSION: MGT is provided under widely varying conditions and regulatory frameworks. The data provided here may be a useful guide for policy action at both governmental and professional levels.

A de novo MLH1 germ line mutation in a 31-year-old colorectal cancer patient.

Hereditary nonpolyposis colorectal cancer is an autosomal dominant cancer predisposition syndrome caused by inherited germ line mutations in DNA mismatch repair genes, predominantly MSH2 and MLH1. Here we report the first proven de novo germ line mutation in MLH1 (c.666dupA) identified in a 31-year-old colorectal cancer patient with the alteration being present in a heterozygous state in all three germ layers and homozygously in his colon cancer. The mutation was absent in both biological parents and all sibs available. Despite extensive polymorphic marker analysis, the parental origin of c.666dupA could not be conclusively determined, representing either a single mutational event in a parental germ cell or (maternal) gonadal mosaicism. Although rare, consequential application of the Bethesda guidelines for genetic testing should allow the clinician to readily identify colorectal cancer patients below age 50 years who carry de novo mismatch repair gene mutations.

Gene conversion is a frequent mechanism of inactivation of the wild-type allele in cancers from MLH1/MSH2 deletion carriers.

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominantly inherited cancer predisposition syndrome caused by germ line mutations in DNA mismatch repair genes, predominantly MLH1 and MSH2, with large genomic rearrangements accounting for 5% to 20% of all mutations. Although crucial to the understanding of cancer initiation, little is known about the second, somatic hit in HNPCC tumorigenesis, commonly referred to as loss of heterozygosity. Here, we applied a recently developed method, multiplex ligation-dependent probe amplification, to study MLH1/MSH2 copy number changes in 16 unrelated Swiss HNPCC patients, whose cancers displayed microsatellite instability and loss of MLH1 or MSH2 expression, but in whom no germ line mutation could be detected by conventional screening. The aims of the study were (a) to determine the proportion of large genomic rearrangements among Swiss MLH1/MSH2 mutation carriers and (b) to investigate the frequency and nature of loss of heterozygosity as a second, somatic event, in tumors from MLH1/MSH2 germ line deletion carriers. Large genomic deletions were found to account for 4.3% and 10.7% of MLH1 and MSH2 mutations, respectively. Multiplex ligation-dependent probe amplification analysis of 18 cancer specimens from two independent sets of Swiss and Finnish MLH1/MSH2 deletion carriers revealed that somatic mutations identical to the ones in the germ line occur frequently in colorectal cancers (6 of 11; 55%) and are also present in extracolonic HNPCC-associated tumors. Chromosome-specific marker analysis implies that loss of the wild-type allele predominantly occurs through locus-restricted recombinational events, i.e., gene conversion, rather than mitotic recombination or deletion of the respective gene locus. (Cancer Res 2006; (66)2: 659-64).

Prevalence of MYH germline mutations in Swiss APC mutation-negative polyposis patients.

In 10-30% of patients with classical familial adenomatous polyposis (FAP) and up to 90% of those with attenuated (<100 colorectal adenomas; AFAP) polyposis, no pathogenic germline mutation in the adenomatous polyposis coli (APC) gene can be identified (APC mutation-negative). Recently, biallelic mutations in the base excision repair gene MYH have been shown to predispose to a multiple adenoma and carcinoma phenotype. This study aimed to (i) assess the MYH mutation carrier frequency among Swiss APC mutation-negative patients and (ii) identify phenotypic differences between MYH mutation carriers and APC/MYH mutation-negative polyposis patients. Seventy-nine unrelated APC mutation-negative Swiss patients with either classical (n=18) or attenuated (n=61) polyposis were screened for germline mutations in MYH by dHPLC and direct genomic DNA sequencing. Overall, 7 (8.9%) biallelic and 9 (11.4%) monoallelic MYH germline mutation carriers were identified. Among patients with a family history compatible with autosomal recessive inheritance (n=45), 1 (10.0%) out of 10 classical polyposis and 6 (17.1%) out of 35 attenuated polyposis patients carried biallelic MYH alterations, 2 of which represent novel gene variants (p.R171Q and p.R231H). Colorectal cancer was significantly (p<0.007) more frequent in biallelic mutation carriers (71.4%) compared with that of monoallelic and MYH mutation-negative polyposis patients (0 and 13.8%, respectively). On the basis of our findings and earlier reports, MYH mutation screening should be considered if all of the following criteria are fulfilled: (i) presence of classical or attenuated polyposis coli, (ii) absence of a pathogenic APC mutation, and (iii) a family history compatible with an autosomal recessive mode of inheritance.

Evidence for genetic anticipation in hereditary non-polyposis colorectal cancer.

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal, dominantly inherited, colorectal cancer (CRC) predisposition syndrome caused by germline mutations in DNA mismatch repair (MMR) genes, predominantly MLH1 and MSH2. Thus far, only limited data exist on the occurrence of genetic anticipation in HNPCC, i.e. the earlier age at diagnosis of CRC in successive generations. Performing nonparametric distribution-free statistical analyses, we investigated 55 parent-child pairs who had been diagnosed with CRC and who came from 21 Swiss HNPCC families with characterised MMR germline mutation (15 in MLH1 and 6 in MSH2). The overall median age at diagnosis was 43 years, with an interquartile range (IQR) of 14 and incidence ages ranging from 18 to 62 years. Descendants of HNPCC patients (median age at diagnosis 39 years, IQR=12) were found to be diagnosed with CRC significantly earlier than their parents (47 years, IQR=10), with the median of the paired age difference amounting to 8 years (IQR=15; P<0.0001). Birth cohort effects could be excluded, since the same, statistically significant, age difference was also observed in the oldest offspring birth cohort (birth year <1916; P=0.01). Genetic anticipation appeared to be more pronounced when the disease allele was transmitted through the father than through the mother (median age difference 11 vs. 4 years, respectively; both P<0.01). If confirmed in larger, ideally prospective studies, these results may have important implications for genetic counselling and clinical management of HNPCC families.