A new bioinformatics tool to help assess the significance of BRCA1 variants.

BACKGROUND: Germline pathogenic variants in the breast cancer type 1 susceptibility gene BRCA1 are associated with a 60% lifetime risk for breast and ovarian cancer. This overall risk estimate is for all BRCA1 variants; obviously, not all variants confer the same risk of developing a disease. In cancer patients, loss of BRCA1 function in tumor tissue has been associated with an increased sensitivity to platinum agents and to poly-(ADP-ribose) polymerase (PARP) inhibitors. For clinical management of both at-risk individuals and cancer patients, it would be important that each identified genetic variant be associated with clinical significance. Unfortunately for the vast majority of variants, the clinical impact is unknown. The availability of results from studies assessing the impact of variants on protein function may provide insight of crucial importance. RESULTS AND CONCLUSION: We have collected, curated, and structured the molecular and cellular phenotypic impact of 3654 distinct BRCA1 variants. The data was modeled in triple format, using the variant as a subject, the studied function as the object, and a predicate describing the relation between the two. Each annotation is supported by a fully traceable evidence. The data was captured using standard ontologies to ensure consistency, and enhance searchability and interoperability. We have assessed the extent to which functional defects at the molecular and cellular levels correlate with the clinical interpretation of variants by ClinVar submitters. Approximately 30% of the ClinVar BRCA1 missense variants have some molecular or cellular assay available in the literature. Pathogenic variants (as assigned by ClinVar) have at least some significant functional defect in 94% of testable cases. For benign variants, 77% of ClinVar benign variants, for which neXtProt Cancer variant portal has data, shows either no or mild experimental functional defects. While this does not provide evidence for clinical interpretation of variants, it may provide some guidance for variants of unknown significance, in the absence of more reliable data. The neXtProt Cancer variant portal ( https://www.nextprot.org/portals/breast-cancer ) contains over 6300 observations at the molecular and/or cellular level for BRCA1 variants.

Risk Analysis of Prostate Cancer in PRACTICAL, a Multinational Consortium, Using 25 Known Prostate Cancer Susceptibility Loci.

BACKGROUND: Genome-wide association studies have identified multiple genetic variants associated with prostate cancer risk which explain a substantial proportion of familial relative risk. These variants can be used to stratify individuals by their risk of prostate cancer. METHODS: We genotyped 25 prostate cancer susceptibility loci in 40,414 individuals and derived a polygenic risk score (PRS). We estimated empirical odds ratios (OR) for prostate cancer associated with different risk strata defined by PRS and derived age-specific absolute risks of developing prostate cancer by PRS stratum and family history. RESULTS: The prostate cancer risk for men in the top 1% of the PRS distribution was 30.6 (95% CI, 16.4-57.3) fold compared with men in the bottom 1%, and 4.2 (95% CI, 3.2-5.5) fold compared with the median risk. The absolute risk of prostate cancer by age of 85 years was 65.8% for a man with family history in the top 1% of the PRS distribution, compared with 3.7% for a man in the bottom 1%. The PRS was only weakly correlated with serum PSA level (correlation = 0.09). CONCLUSIONS: Risk profiling can identify men at substantially increased or reduced risk of prostate cancer. The effect size, measured by OR per unit PRS, was higher in men at younger ages and in men with family history of prostate cancer. Incorporating additional newly identified loci into a PRS should improve the predictive value of risk profiles. IMPACT: We demonstrate that the risk profiling based on SNPs can identify men at substantially increased or reduced risk that could have useful implications for targeted prevention and screening programs.

High-resolution breakpoint analysis provides evidence for the sequence-directed nature of genome rearrangements in hereditary disorders.

Although most of the pertinent data on the sequence-directed processes leading to genome rearrangements (GRs) have come from studies on somatic tissues, little is known about GRs in the germ line of patients with hereditary disorders. This study aims at identifying DNA motifs and higher order structures of genome architecture, which can result in losses and gains of genetic material in the germ line. We first identified candidate motifs by studying 112 pathogenic germ-line GRs in hereditary colorectal cancer patients, and subsequently created an algorithm, termed recombination type ratio, which correctly predicts the propensity of rearrangements with respect to homologous versus nonhomologous recombination events.

Recurrence and variability of germline EPCAM deletions in Lynch syndrome.

Recently, we identified 3' end deletions in the EPCAM gene as a novel cause of Lynch syndrome. These truncating EPCAM deletions cause allele-specific epigenetic silencing of the neighboring DNA mismatch repair gene MSH2 in tissues expressing EPCAM. Here we screened a cohort of unexplained Lynch-like families for the presence of EPCAM deletions. We identified 27 novel independent MSH2-deficient families from multiple geographical origins with varying deletions all encompassing the 3' end of EPCAM, but leaving the MSH2 gene intact. Within The Netherlands and Germany, EPCAM deletions appeared to represent at least 2.8% and 1.1% of the confirmed Lynch syndrome families, respectively. MSH2 promoter methylation was observed in epithelial tissues of all deletion carriers tested, thus confirming silencing of MSH2 as the causative defect. In a total of 45 families, 19 different deletions were found, all including the last two exons and the transcription termination signal of EPCAM. All deletions appeared to originate from Alu-repeat mediated recombination events. In 17 cases regions of microhomology around the breakpoints were found, suggesting nonallelic homologous recombination as the most likely mechanism. We conclude that 3' end EPCAM deletions are a recurrent cause of Lynch syndrome, which should be implemented in routine Lynch syndrome diagnostics.

Risk of colorectal and endometrial cancers in EPCAM deletion-positive Lynch syndrome: a cohort study.

BACKGROUND: Lynch syndrome is caused by germline mutations in MSH2, MLH1, MSH6, and PMS2 mismatch-repair genes and leads to a high risk of colorectal and endometrial cancer. We previously showed that constitutional 3' end deletions of EPCAM can cause Lynch syndrome through epigenetic silencing of MSH2 in EPCAM-expressing tissues, resulting in tissue-specific MSH2 deficiency. We aim to establish the risk of cancer associated with such EPCAM deletions. METHODS: We obtained clinical data for 194 carriers of a 3' end EPCAM deletion from 41 families known to us at the Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands and compared cancer risk with data from a previously described cohort of 473 carriers from 91 families with mutations in MLH1, MSH2, MSH6, or a combined EPCAM-MSH2 deletion. FINDINGS: 93 of the 194 EPCAM deletion carriers were diagnosed with colorectal cancer; three of the 92 women with EPCAM deletions were diagnosed with endometrial cancer. Carriers of an EPCAM deletion had a 75% (95% CI 65-85) cumulative risk of colorectal cancer before the age of 70 years (mean age at diagnosis 43 years [SD 12]), which did not differ significantly from that of carriers of combined EPCAM-MSH2 deletion (69% [95% CI 47-91], p=0·8609) or mutations in MSH2 (77% [64-90], p=0·5892) or MLH1 (79% [68-90], p=0·5492), but was higher than noted for carriers of MSH6 mutation (50% [38-62], p<0·0001). By contrast, women with EPCAM deletions had a 12% [0-27] cumulative risk of endometrial cancer, which was lower than was that noted for carriers of a combined EPCAM-MSH2 deletion (55% [20-90], p<0·0001) or of a mutation in MSH2 (51% [33-69], p=0·0006) or MSH6 (34% [20-48], p=0·0309), but did not differ significantly from that noted for MLH1 (33% [15-51], p=0·1193) mutation carriers. This risk seems to be restricted to deletions that extend close to the MSH2 gene promoter. Of 194 carriers of an EPCAM deletion, three had duodenal cancer and four had pancreatic cancer. INTERPRETATION: EPCAM deletion carriers have a high risk of colorectal cancer; only those with deletions extending close to the MSH2 promoter have an increased risk of endometrial cancer. These results underscore the effect of mosaic MSH2 deficiency, leading to variable cancer risks, and could form the basis of an optimised protocol for the recognition and targeted prevention of cancer in EPCAM deletion carriers.

Selection of patients with germline MLH1 mutated Lynch syndrome by determination of MLH1 methylation and BRAF mutation.

Lynch syndrome is one of the most common hereditary colorectal cancer (CRC) syndrome and is caused by germline mutations of MLH1, MSH2 and more rarely MSH6, PMS2, MLH3 genes. Whereas the absence of MSH2 protein is predictive of Lynch syndrome, it is not the case for the absence of MLH1 protein. The purpose of this study was to develop a sensitive and cost effective algorithm to select Lynch syndrome cases among patients with MLH1 immunohistochemical silencing. Eleven sporadic CRC and 16 Lynch syndrome cases with MLH1 protein abnormalities were selected. The BRAF c.1799T> A mutation (p.Val600Glu) was analyzed by direct sequencing after PCR amplification of exon 15. Methylation of MLH1 promoter was determined by Methylation-Sensitive Single-Strand Conformation Analysis. In patients with Lynch syndrome, there was no BRAF mutation and only one case showed MLH1 methylation (6%). In sporadic CRC, all cases were MLH1 methylated (100%) and 8 out of 11 cases carried the above BRAF mutation (73%) whereas only 3 cases were BRAF wild type (27%). We propose the following algorithm: (1) no further molecular analysis should be performed for CRC exhibiting MLH1 methylation and BRAF mutation, and these cases should be considered as sporadic CRC; (2) CRC with unmethylated MLH1 and negative for BRAF mutation should be considered as Lynch syndrome; and (3) only a small fraction of CRC with MLH1 promoter methylation but negative for BRAF mutation should be true Lynch syndrome patients. These potentially Lynch syndrome patients should be offered genetic counselling before searching for MLH1 gene mutations.

Identification of seven new prostate cancer susceptibility loci through a genome-wide association study.

Prostate cancer (PrCa) is the most frequently diagnosed cancer in males in developed countries. To identify common PrCa susceptibility alleles, we previously conducted a genome-wide association study in which 541,129 SNPs were genotyped in 1,854 PrCa cases with clinically detected disease and in 1,894 controls. We have now extended the study to evaluate promising associations in a second stage in which we genotyped 43,671 SNPs in 3,650 PrCa cases and 3,940 controls and in a third stage involving an additional 16,229 cases and 14,821 controls from 21 studies. In addition to replicating previous associations, we identified seven new prostate cancer susceptibility loci on chromosomes 2, 4, 8, 11 and 22 (with P = 1.6 x 10(-8) to P = 2.7 x 10(-33)).

Age-Dependent Cancer Risk Is Not Different in between MSH2 and MLH1 Mutation Carriers.

Lynch syndrome is mostly characterized by early-onset colorectal and endometrial adenocarcinomas. Over 90% of the causal mutations occur in two mismatch repair genes, MSH2 and MLH1. The aim of this study was to evaluate the age-dependent cancer risk in MSH2 or MLH1 mutation carriers from data of DNA diagnostic laboratories. To avoid overestimation, evaluation was based on the age-dependent proportion of mutation carriers in asymptomatic first-degree relatives of identified mutation carriers. Data from 859 such eligible relatives were collected from 8 centers; 387 were found to have inherited the mutation from their relatives. Age-dependent risks were calculated either using a nonparametric approach for four discrete age groups or assuming a modified Weibull distribution for the dependence of risk on age. Cancer risk was estimated starting at 28 (25-32 0.68 confidence interval) and to reach near 0.70 at 70 years. The risks were very similar for MSH2 and MLH1 mutation carriers. Although not statistically significant, the risk in males appeared to precede that for females by ten years. This difference needs to be investigated on a larger dataset. If confirmed, this would indicate that the onset of the colonoscopic surveillance may be different in male and female mutation carriers.

Multiple novel prostate cancer predisposition loci confirmed by an international study: the PRACTICAL Consortium.

A recent genome-wide association study found that genetic variants on chromosomes 3, 6, 7, 10, 11, 19 and X were associated with prostate cancer risk. We evaluated the most significant single-nucleotide polymorphisms (SNP) in these loci using a worldwide consortium of 13 groups (PRACTICAL). Blood DNA from 7,370 prostate cancer cases and 5,742 male controls was analyzed by genotyping assays. Odds ratios (OR) associated with each genotype were estimated using unconditional logistic regression. Six of the seven SNPs showed clear evidence of association with prostate cancer (P = 0.0007-P = 10(-17)). For each of these six SNPs, the estimated per-allele OR was similar to those previously reported and ranged from 1.12 to 1.29. One SNP on 3p12 (rs2660753) showed a weaker association than previously reported [per-allele OR, 1.08 (95% confidence interval, 1.00-1.16; P = 0.06) versus 1.18 (95% confidence interval, 1.06-1.31)]. The combined risks associated with each pair of SNPs were consistent with a multiplicative risk model. Under this model, and in combination with previously reported SNPs on 8q and 17q, these loci explain 16% of the familial risk of the disease, and men in the top 10% of the risk distribution have a 2.1-fold increased risk relative to general population rates. This study provides strong confirmation of these susceptibility loci in multiple populations and shows that they make an important contribution to prostate cancer risk prediction.

Rapidly evolving Rab GTPase paralogs and reproductive isolation in Drosophila.

Alterations at the X-linked Hmr gene of Drosophila melanogaster can fully restore viability and partially restore fertility in hybrid flies from crosses between D. melanogaster and any of its three most closely related species. Although more than one gene is expected to be involved in these barriers to reproduction, a single DNA-binding protein was recently identified as HMR. The Hmr gene was shown to evolve unusually fast, a feature that supports its role in causing genetic incompatibility in a hybrid genotype. The current treatment of hybrid genetics focuses not only on Hmr but also on the Rab9D gene, which lies only 1kb from Hmr. Rab9D is proposed also to influence hybrid viability. This gene has remained tightly linked to Hmr for about 10 million years, but it has diverged even more than Hmr with regard to D. melanogaster and its most closely related species. Furthermore, the 197-amino acid RAB9D protein contains four amino acid substitutions in the D. melanogaster-rescuing mutant Hmr1. Rab9D is shown to have evolved under very strong positive selection and to be the most recent member of a cluster of six paralogs that encode small RAB GTPases. Four of the six paralogs are unique to D. melanogaster in which they have diverged considerably, their encoded proteins sharing less than 50% amino acid identities with proteins from their orthologs in the closest species. Only two Rab orthologs are present in these sibling species and none is present in the genomes of more distantly related Drosophila species. Rapidly evolving Rab paralogs near the Hmr locus probably developed functional specialization of redundant proteins involved in trafficking macromolecules between cytoplasm and nucleus. Positive selection acting on duplicates of these Rab genes appears to participate in reproductive isolation.

Double frameshift mutations in APC and MSH2 in the same individual.

Heterozygous germline DNA mismatch repair gene mutations are typically associated with HNPCC. Here we report the case of a proband whose father was known for familial adenomatous polyposis. The number of polyps (less than ten) was not typical of polyposis; therefore, the diagnosis of HNPCC was entertained. Microsatellite instability analyses were performed on peripheral blood and biopsy of a right-sided dysplastic adenoma. The tumor tissue showed high-grade instability, and a subsequent, immunohistochemistry showed that neither MSH2 nor MSH6 proteins were expressed in tumor cells. Prophylactic colectomy was performed, and an adenocarcinoma developing within the adenoma was diagnosed (pT1N0). Genomic DNA analysis revealed a novel mutation in MSH2 as a frameshift mutation in exon 7 (c.1191_1192dupG). Both parents of the proband were analysed for MSH2 and APC mutations, and in the father, a truncating mutation in exon 15 of APC was identified as del3471-3473GAGA. This mutation was found to be present in the proband. His mother was found to bear the MSH2 exon 7 mutation. At the follow-up, the proband was diagnosed with fundic, antral and duodenal adenomas (one fundic adenoma showed low-grade dysplasia). Several tubular rectal adenomas with low-grade dysplasia were excised. The patient later developed an intra-abdominal desmoid tumor.

Distinct patterns of germ-line deletions in MLH1 and MSH2: the implication of Alu repetitive element in the genetic etiology of Lynch syndrome (HNPCC).

A relatively high frequency of germ-line genomic rearrangements in MLH1 and MSH2 has been reported among Lynch Syndrome (HNPCC) patients from different ethnic populations. To investigate the underlying molecular mechanisms, we characterized the DNA breakpoints of 11 germ-line deletions, six for MLH1 and five for MSH2. Distinct deletion patterns were found for the two genes. The five cases of MSH2 deletions result exclusively from intragenic unequal recombination mediated by repetitive Alu sequences. In contrast, five out of the six MLH1 deletions are due to recombinations involving sequences of no significant homology (P=0.015). A detailed analysis of the DNA breakpoints in the two genes, previously characterized by other groups, validated the observation that Alu-mediated unequal recombination is the main type of deletion in MSH2 (n=34), but not in MLH1 (n=21) (P<0.0001). Plotting the distribution of known DNA breakpoints among the introns of the two genes showed that, the highest breakpoint density is co-localized with the highest Alu density. Our study suggests that Alu is a promoting factor for the genomic recombinations in both MLH1 and MSH2, and the local Alu density may be involved in shaping the deletion pattern.

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.

An unexpected Cowden syndrome case found among members of a large familial adenomatous polyposis kindred.

Genetic testing is now considered the standard of care in the management of familial adenomatous polyposis (FAP). Non-carriers of mutations are excluded from endoscopic surveillance. During the systematic screening of the relatives of an affected member with FAP, one non-carrier of APC mutations was unexpectedly found with the typical Cowden syndrome phenotype. One large Algerian family with FAP was screened for an APC germline mutation. Moreover, we also performed a mutation search in the Cowden syndrome member for PTEN, BMPR1A or MADH4 (SMAD4) germline mutations. We identified a mutation in the APC gene that results in a truncated protein (Y935X) in the FAP proband, and subsequently in 12 FAP-affected members. Among the 12 APC mutation-negative members of this family, we found one member with the Cowden disease phenotype. However, the mutation analysis in the PTEN gene and the two other genes involved in juvenile polyposis, namely BMPR1A and MADH4 (SMAD4), in the Cowden syndrome patient failed to show any pathogenic mutation. Genetic testing is a powerful tool that can provide a definitive diagnosis for FAP. However, not all polyposes in the FAP family are adenomatous polyposes.

Molecular characterization of the spectrum of genomic deletions in the mismatch repair genes MSH2, MLH1, MSH6, and PMS2 responsible for hereditary nonpolyposis colorectal cancer (HNPCC).

A systematic search by Southern blot analysis in a cohort of 439 hereditary nonpolyposis colorectal cancer (HNPCC) families for genomic rearrangements in the main mismatch repair (MMR) genes, namely, MSH2, MLH1, MSH6, and PMS2, identified 48 genomic rearrangements causative of this inherited predisposition to colorectal cancer in 68 unrelated kindreds. Twenty-nine of the 48 rearrangements were found in MSH2, 13 in MLH1, 2 in MSH6, and 4 in PMS2. The vast majority were deletions, although one previously described large inversion, an intronic insertion, and a more complex rearrangement also were found. Twenty-four deletion breakpoints have been identified and sequenced in order to determine the underlying recombination mechanisms. Most fall within repetitive sequences, mainly Alu repeats, in agreement with the differential distribution of deletions between the MSH2 and MLH1 genes: the higher number and density of Alu repeats in MSH2 corresponded with a higher incidence of genomic rearrangement at this disease locus when compared with other MMR genes. Long interspersed nuclear element (LINE) repeats, relatively abundant in, for example, MLH1, did not seem to contribute to the genesis of the deletions, presumably because of their older evolutionary age and divergence among individual repeat units when compared with short interspersed nuclear element (SINE) repeats, including Alu repeats. Moreover, Southern blot analysis of the introns and the genomic regions flanking the MMR genes allowed us to detect 6 novel genomic rearrangements that left the coding region of the disease-causing gene intact. These rearrangements comprised 4 deletions upstream of the coding region of MSH2 (3 cases) and MSH6 (1 case), a 2-kb insertion in intron 7 of PMS2, and a small (459-bp) deletion in intron 13 of MLH1. The characterization of these genomic rearrangements underlines the importance of genomic deletions in the etiology of HNPCC and will facilitate the development of PCR-based tests for their detection in diagnostic laboratories.

Double frameshift mutations in APC and MSH2 in the same individual.

Heterozygous germline DNA mismatch repair gene mutations are typically associated with HNPCC. Here we report the case of a proband whose father was known for familial adenomatous polyposis. The number of polyps (less than ten) was not typical of polyposis; therefore, the diagnosis of HNPCC was entertained. Microsatellite instability analyses were performed on peripheral blood and biopsy of a right-sided dysplastic adenoma. The tumour tissue showed high-grade instability, and subsequently, immunohistochemistry showed that neither MSH2 nor MSH6 proteins were expressed in tumour cells. Prophylactic colectomy was performed, and an adenocarcinoma developing within the adenoma was diagnosed (pT1N0). Genomic DNA analysis revealed a novel mutation in MSH2 as a frameshift mutation in exon 7 (c.1,191_1,192dupG). Both parents of the proband were analyzed for MSH2 and APC mutations, and in the father, a truncating mutation in exon 15 of APC was identified as del3471-3473GAGA. This mutation was found to be present in the proband. His mother was found to bear the MSH2 exon 7 mutation. At follow-up, the proband was diagnosed with fundic, antral and duodenal adenomas (one fundic adenoma showed low-grade dysplasia). Several tubular rectal adenomas with low-grade dysplasia were excised. The patient later developed an intra-abdominal desmoid tumour.

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.