C. Tops

Multiplicity in polyp count and extracolonic manifestations in 40 Dutch patients with MYH associated polyposis coli (MAP)

Objective: To investigate the contribution of MYH associated polyposis coli (MAP) among polyposis families in the Netherlands, and the prevalence of colonic and extracolonic manifestations in MAP patients. Methods: 170 patients with polyposis coli, who previously tested negative for APC mutations, were screened by denaturing gradient gel electrophoresis and direct sequencing to identify MYH germline mutations. Results: Homozygous and compound heterozygous MYH mutations were identified in 40 patients (24%). No difference was found in the percentage of biallelic mutation carriers between patients with 10–99 polyps or 100–1000 polyps (29% in both groups). Colorectal cancer was found in 26 of the 40 patients with MAP (65%) within the age range 21 to 67 years (median 45). Complete endoscopic reports were available for 16 MAP patients and revealed five cases with gastro-duodenal polyps (31%), one of whom also presented with a duodenal carcinoma. Breast cancer occurred in 18% of female MAP patients, significantly more than expected from national statistics (standardised morbidity ratio = 3.75). Conclusions: Polyp numbers in MAP patients were equally associated with the attenuated and classical polyposis coli phenotypes. Two thirds of the MAP patients had colorectal cancer, 95% of whom were older than 35 years, and one third of a subset of patients had upper gastrointestinal lesions. Endoscopic screening of the whole intestine should be carried out every two years for all MAP patients, starting from age 25–30 years. The frequent occurrence of additional extraintestinal manifestations, such as breast cancer among female MAP patients, should be thoroughly investigated.

Molecular genetic tests as a guide to surgical management of familial adenomatous polyposis

BACKGROUND In familial adenomatous polyposis the only curative treatment is colectomy, and the choice of operation lies between restorative proctocolectomy (RPC) and colectomy with ileorectal anastomosis (IRA). The RPC procedure carries a higher morbidity but, unlike IRA, removes the risk of subsequent rectal cancer. Since the course of familial adenomatous polyposis is influenced by the site of mutation in the polyposis gene, DNA analysis might be helpful in treatment decisions. METHODS We evaluated the incidence of rectal cancer in polyposis patients who had undergone IRA, and examined whether the requirement for subsequent rectal excision because of cancer or uncontrollable polyps was related to the site of mutation. FINDINGS Between 1956 and mid-1995, 225 patients registered at the Netherlands Polyposis Registry had undergone IRA. In 87 of them, a pathogenetic mutation was detected. 72 patients had a mutation located before codon 1250 and 15 patients after this codon. The cumulative risk of rectal cancer 20 years after surgery was 12%, and at that time 42% had undergone rectal excision. The risk of secondary surgery was higher in patients with mutations in the region after codon 1250 than in patients with mutations before this codon (relative risk 2.7, p < 0.05). INTERPRETATION On this evidence, IRA should be the primary treatment for polyposis in patients with mutations before codon 1250, and RPC in those with mutations after this codon.

Atypical HNPCC owing to MSH6 germline mutations: analysis of a large Dutch pedigree

Hereditary non-polyposis colorectal cancer (HNPCC) is the most common genetic susceptibility syndrome for colorectal cancer. HNPCC is most frequently caused by germline mutations in the DNA mismatch repair (MMR) genes MSH2 andMLH1. Recently, mutations in another MMR gene, MSH6 (also known asGTBP), have also been shown to result in HNPCC. Preliminary data indicate that the phenotype related toMSH6 mutations may differ from the classical HNPCC caused by defects in MSH2 andMLH1.  Here, we describe an extended Dutch HNPCC family not fulfilling the Amsterdam criteria II and resulting from aMSH6 mutation. Overall, the penetrance of colorectal cancer appears to be significantly decreased (p<0.001) among the MSH6 mutation carriers in this family when compared with MSH2 andMLH1 carriers (32% by the age of 80v >80%).  Endometrial cancer is a frequent manifestation among female carriers (six out of 13 malignant tumours). Transitional cell carcinoma of the urinary tract is also relatively common in both male and female carriers (10% of the carriers).  Moreover, the mean age of onset of both colorectal cancer (MSH6 v MSH2/MLH1 = 55 yearsv 44/41 years) and endometrial carcinomas (MSH6 v MSH2/MLH1 = 55 yearsv 49/48 years) is delayed. As previously reported, we confirm that the pattern of microsatellite instability, in combination with immunohistochemical analysis, can predict the presence of a MSH6 germline defect.  The detailed characterisation of the clinical phenotype of this kindred contributes to the establishment of genotype-phenotype correlations in HNPCC owing to mutations in specific mismatch repair genes.

Close linkage of a highly polymorphic marker (D5S37) to familial adenomatous polyposis (FAP) and confirmation of FAP localization on chromosome 5q21-q22.

SummaryFifteen apparently unrelated Dutch families with familial adenomatous polyposis (FAP) also known as familial polyposis coli (FPC; McKusick No. 17510) were screened for linkage with the DNA probe C11p11 localized on chromosome 5q21–22 and previously reported to be closely linked to FAP (Bodmer et al. 1987; Leppert et al. 1987). In our study C11p11 was minimally informative, which is ascribable to its low heterozygosity in the North European populations. Of the above families, 12 were investigated also for linkage with D5S37 (DNA probe Pi227). Data from 11 of them were found to be informative and showed that FAP is closely linked to D5S37 previously localized on chromosome 5q21 (peak lod score 7.85 at a recombination fraction of 0.048 with 95% probability limits 0.005–0.145). Results discussed below indicate for the first time that the most likely location of the FAP gene is in the band 5q22 very close to 5q21, if not in the transitional zone between these two bands. The probe Pi227 recognizes 4 restriction fragment length polymorphism (RFLP) sites, exhibiting a total of 9 alleles with 24 theoretically possible haplotypes in the Dutch population. Therefore, this probe appears to have potential as a generally useful predictive marker for FAP until much closer and similarly useful markers become available.

Enrichment of Low Penetrance Susceptibility Loci in a Dutch Familial Colorectal Cancer Cohort

Recent genome-wide association studies have identified several loci that confer an increased risk of colorectal cancer (CRC). We studied the role of the 8q24.21 (rs6983267), 18q21.1 (rs12953717), 15q13.3 (rs4779584), 11q23.1 (rs3802842), 8q23.3 (rs16892766), and 10p14 (rs10795668) risk variants in a series of 995 Dutch CRC cases and 1340 controls. The CRC cases were selected on basis of having a family history of CRC and/or early-onset disease. The detailed clinical and molecular data available on the cases allowed us to examine the relationship between risk variants and clinicopathologic characteristics. We replicated the association with an increased risk of CRC cancer for all loci, except 10p14. The association with the variant on chromosome 15q13.3 was confirmed for the first time. The risks associated with variants in our series were higher (not significant) than those previously reported, consistent with our series reflecting genetic enrichment. Moreover, we show that familial CRC cases possess an increased number of risk alleles compared with solitary CRC cases (early-onset; mean age at diagnosis of 48.5 years). We also identified a significant increase in the number of risk alleles in families with early-onset disease (≤50 years) compared with late-onset families (>50 years). In solitary CRC patients, enrichment for risk alleles was not observed, suggesting that other causes of increased CRC risk play a role in these cases. Overall, our results suggest that clustering of low-risk variants may explain part of the excess risk in CRC families. (Cancer Epidemiol Biomarkers Prev 2009;18(11):3062–7)

PRESYMPTOMATIC DIAGNOSIS OF FAMILIAL ADENOMATOUS POLYPOSIS BY BRIDGING DNA MARKERS

Familial adenomatous polyposis (FAP) is a disorder with autosomal dominant inheritance, which predisposes to colorectal adenocarcinoma. The gene causing the disorder has been assigned to chromosome 5 by means of a polymorphic DNA marker called C11p11. An informative Dutch pedigree showed that two other linked polymorphic DNA markers, Pi227 and YN5.48, closely flank the FAP locus, one on either side. This finding will allow prenatal and presymptomatic diagnosis of FAP, with more than 99.9% reliability in the majority of families, by means of already available markers.

Identification of HNPCC by Molecular Analysis of Colorectal and Endometrial Tumors

Hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) is a dominantly inherited syndrome characterized by the development of colorectal cancer, endometrial cancer and other cancers and the presence of microsatellite instability (MSI) in tumors. The Bethesda guidelines have been proposed for the identification of families suspected of HNPCC that require further molecular analysis. We have evaluated the yield of MSI-analysis in a large series of Dutch families suspected of HNPCC. We also analysed whether the loss of mismatch repair (MMR) protein detected by immunohistochemistry (IHC) of colorectal cancer (CRC) and endometrial cancer correlated with the presence of MSI and/or a MMR gene mutation. The results showed that the Bethesda criteria with a few modifications are appropriate to identify families eligible for genetic testing. In addition, we found that MSI and IHC-analysis of CRC using antibodies against MLH1, MSH2, MSH6 and PMS2 proteins are equally effective for identifying carriers of the known MMR gene defects. However, as long as the role of other putative MMR genes in hereditary CRC has not been elucidated, IHC-analysis cannot completely replace MSI. For this reason, we prefer MSI-analysis as first step in families suspected of HNPCC. On the other hand, in families fulfilling the revised Amsterdam criteria in which the probability of detecting a mutation is relatively high, we would recommend IHC as first diagnostic step because the result might predict the specific underlying MMR gene mutation. MSI or IHC-analysis of endometrial cancer alone was found to be less sensitive compared with these tests performed in colorectal cancer. Therefore, probably the best approach in the analysis of this cancer is to perform both techniques. The identification of HNPCC is important as it makes it possible to target effective preventative measures. Our studies showed that MSI and IHC analysis of colorectal and endometrial cancer, are reliable cost-effective tools that can be used to identify patients with HNPCC.

High frequency of copy‐neutral LOH in MUTYH‐associated polyposis carcinomas

Genetic instability is known to drive colorectal carcinogenesis. Generally, a distinction is made between two types of genetic instability: chromosomal instability (CIN) and microsatellite instability (MIN or MSI). Most CIN tumours are aneuploid, whereas MSI tumours are considered near‐diploid. However, for MUTYH‐associated polyposis (MAP) the genetic instability involved in the carcinogenesis remains unclear, as near‐diploid adenomas, aneuploid adenomas and near‐diploid carcinomas have been reported. Remarkably, our analysis of 26 MAP carcinomas, using SNP arrays and flow sorting, showed that these tumours are often near‐diploid (52%) and mainly contain chromosomal regions of copy‐neutral loss of heterozygosity (LOH) (71%). This is in contrast to sporadic colon cancer, where physical loss is the main characteristic. The percentage of chromosomal gains (24%) is comparable to sporadic colorectal cancers with CIN. Furthermore, we verified our scoring of copy‐neutral LOH versus physical loss in MAP carcinomas by two methods: fluorescence in situ hybridization, and LOH analysis using polymorphic markers on carcinoma fractions purified by flow sorting. The results presented in this study suggest that copy‐neutral LOH is an important mechanism in the tumorigenesis of MAP. Copyright

Genetic testing in hereditary non-polyposis colorectal cancer families with a MSH2 , MLH1 , or MSH6 mutation

About 5% of colorectal cancers are associated with the autosomal dominantly inherited cancer susceptibility syndrome hereditary non-polyposis colorectal cancer (HNPCC).1,2 HNPCC is characterised by a high risk of developing colorectal cancer and endometrial cancer at a young age (cumulative lifetime risk 80-90% and 30-40%, respectively), and by an increased risk of developing various other tumour types, such as ovarian, uroepithelial, small intestine, biliary tract, stomach, brain, and skin cancers.2–5 Germline mutations in one of three mismatch repair genes ( MSH2 , MLH1 , and MSH6 ) were found to be responsible for a majority of HNPCC families.6–9 Knowledge of the causative mutation in a particular HNPCC family enables the identification of at risk family members by genetic testing. Clearly, the absence or presence of a mutation is of considerable medical and psychological significance. Subjects not carrying the mutation are relieved from a continuous anxiety and can be dismissed from medical surveillance, saving them trouble and reducing health care costs.10 Importantly, subjects with the mutation can benefit from a medical surveillance programme. For HNPCC, colonoscopy has been shown to be a potent tool for the detection and treatment of premalignant adenomas or early colorectal carcinomas in at risk subjects, reducing the risk of developing colorectal cancer and decreasing the overall mortality by about 65%.11,12 The possibility of early detection of colorectal cancer by stool analysis using the genetic markers TP53, BAT26, and K-RAS raises expectations for the development of less invasive surveillance procedures.13 Furthermore, intervention trials with non-steroidal anti-inflammatory drugs (NSAID) in subjects at risk for developing colorectal cancer are in progress.14,15 So far, studies on the use of genetic testing in HNPCC families have used families or subjects who had been registered for research purposes.10,16,17 It is …

High prevalence of founder mutations of the succinate dehydrogenase genes in the Netherlands

Hensen EF, van Duinen N, Jansen JC, Corssmit EPM, Tops CMJ, Romijn JA, Vriends AHJT, van der Mey AGL, Cornelisse CJ, Devilee P, Bayley JP. High prevalence of founder mutations of the succinate dehydrogenase genes in the Netherlands.