Laure Barjhoux

Association of the Variants CASP8 D302H and CASP10 V410I with Breast and Ovarian Cancer Risk in BRCA1 and BRCA2 Mutation Carriers

Background: The genes caspase-8 (CASP8) and caspase-10 (CASP10) functionally cooperate and play a key role in the initiation of apoptosis. Suppression of apoptosis is one of the major mechanisms underlying the origin and progression of cancer. Previous case-control studies have indicated that the polymorphisms CASP8 D302H and CASP10 V410I are associated with a reduced risk of breast cancer in the general population. Methods: To evaluate whether the CASP8 D302H (CASP10 V410I) polymorphisms modify breast or ovarian cancer risk in BRCA1 and BRCA2 mutation carriers, we analyzed 7,353 (7,227) subjects of white European origin provided by 19 (18) study groups that participate in the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA). A weighted cohort approach was used to estimate hazard ratios (HR) and 95% confidence intervals (95% CI). Results: The minor allele of CASP8 D302H was significantly associated with a reduced risk of breast cancer (per-allele HR, 0.85; 95% CI, 0.76-0.97; Ptrend = 0.011) and ovarian cancer (per-allele HR, 0.69; 95% CI, 0.53-0.89; Ptrend = 0.004) for BRCA1 but not for BRCA2 mutation carriers. The CASP10 V410I polymorphism was not associated with breast or ovarian cancer risk for BRCA1 or BRCA2 mutation carriers. Conclusions: CASP8 D302H decreases breast and ovarian cancer risk for BRCA1 mutation carriers but not for BRCA2 mutation carriers. Impact: The combined application of these and other recently identified genetic risk modifiers could in the future allow better individual risk calculation and could aid in the individualized counseling and decision making with respect to preventive options in BRCA1 mutation carriers. Cancer Epidemiol Biomarkers Prev; 19(11); 2859–68. ©2010 AACR.

The rs2910164:G>C SNP in the MIR146A gene is not associated with breast cancer risk in BRCA1 and BRCA2 mutation carriers.

The rs2910164:G>C SNP is located in the gene for miR‐146a, a microRNA that binds the 3′ UTR of the BRCA1 transcript. Preliminary data based on the analysis of a small number of cases suggested that this single nucleotide polymorphism (SNP) might be associated with the age of onset of familial breast and ovarian cancer. This effect was not confirmed on a large series of familial breast cancer cases negative for a BRCA1 or BRCA2 mutation. We show here a lack of association of the rs2910164:G>C SNP with breast cancer risk in a series of 1,166 BRCA1 and 560 BRCA2 mutation carriers. In conclusion, the polymorphism in the miR‐146a gene is unlikely to be of substantial significance regarding breast cancer risk. Hum Mutat 32:1–4, 2011.

Common Genetic Variation at BARD1 Is Not Associated with Breast Cancer Risk in BRCA1 or BRCA2 Mutation Carriers

Background: Inherited BRCA1 and BRCA2 (BRCA1/2) mutations confer elevated breast cancer risk. Knowledge of factors that can improve breast cancer risk assessment in BRCA1/2 mutation carriers may improve personalized cancer prevention strategies. Methods: A cohort of 5,546 BRCA1 and 2,865 BRCA2 mutation carriers was used to evaluate risk of breast cancer associated with BARD1 Cys557Ser. In a second nonindependent cohort of 1,537 of BRCA1 and 839 BRCA2 mutation carriers, BARD1 haplotypes were also evaluated. Results: The BARD1 Cys557Ser variant was not significantly associated with risk of breast cancer from single SNP analysis, with a pooled effect estimate of 0.90 (95% CI: 0.71–1.15) in BRCA1 carriers and 0.87 (95% CI: 0.59–1.29) in BRCA2 carriers. Further analysis of haplotypes at BARD1 also revealed no evidence that additional common genetic variation not captured by Cys557Ser was associated with breast cancer risk. Conclusion: Evidence to date does not support a role for BARD1 variation, including the Cy557Ser variant, as a modifier of risk in BRCA1/2 mutation carriers. Impact: Interactors of BRCA1/2 have been implicated as modifiers of BRCA1/2-associated cancer risk. Our finding that BARD1 does not contribute to this risk modification may focus research on other genes that do modify BRCA1/2-associated cancer risk. Cancer Epidemiol Biomarkers Prev; 20(5); 1032–8. ©2011 AACR.

Direct Visualization of the Highly Polymorphic RNU2 Locus in Proximity to the BRCA1 Gene

Although the breast cancer susceptibility gene BRCA1 is one of the most extensively characterized genetic loci, much less is known about its upstream variable number tandem repeat element, the RNU2 locus. RNU2 encodes the U2 small nuclear RNA, an essential splicing element, but this locus is missing from the human genome assembly due to the inherent difficulty in the assembly of repetitive sequences. To fill the gap between RNU2 and BRCA1, we have reconstructed the physical map of this region by re-examining genomic clone sequences of public databases, which allowed us to precisely localize the RNU2 array 124 kb telomeric to BRCA1. We measured by performing FISH analyses on combed DNA for the first time the exact number of repeats carried by each of the two alleles in 41 individuals and found a range of 6-82 copies and a level of heterozygosity of 98%. The precise localisation of the RNU2 locus in the genome reference assembly and the implementation of a new technical tool to study it will make the detailed exploration of this locus possible. This recently neglected macrosatellite could be valuable for evaluating the potential role of structural variations in disease due to its location next to a major cancer susceptibility gene.

CAG repeat size in Huntingtin alleles is associated with cancer prognosis

The abnormal expansion of a ≥36 CAG unit tract in the Huntingtin gene (HTT) leads to Huntingtons disease (HD), but has also been associated with cancer: the incidence of cancer is lower in HD patients than in age-matched controls, but HD-causing variants of HTT accelerate the progression of breast tumors and the development of metastases in mouse models of breast cancer. To investigate the relationship between HTT CAGs and cancer, data concerning 2407 women with BRCA1 or BRCA2 mutations that predispose to breast and ovarian cancers and 431 patients with breast cancer without family histories were studied; the size of the CAG expansions on both HTT alleles was determined in each subject. The proportion of individuals carrying a CAG expansion in a pathological range for HD was 10 times more frequent than previously reported in the literature. In carriers of BRCA2 mutations, the length of the HTT CAG tract was correlated with lower incidence of ovarian cancer. Among carriers of BRCA1 mutations who developed a breast cancer, its onset occurred 2.4 years earlier in individuals with intermediate HTT alleles (≥27) than in those with a CAG tract <27. Finally, in patients with sporadic HER2 breast cancer, metastasis increased by a factor of 11.10 per 10 additional CAG repeats in HTT. We concluded that whereas long CAG length could be associated with lower cancer incidence, it could also be paradoxically associated with cancer severity (age of apparition and metastasis development).

Targeted Sequencing of the Mitochondrial Genome of Women at High Risk of Breast Cancer without Detectable Mutations in BRCA1/2

Breast Cancer is a complex multifactorial disease for which high-penetrance mutations have been identified. Approaches used to date have identified genomic features explaining about 50% of breast cancer heritability. A number of low- to medium penetrance alleles (per-allele odds ratio < 1.5 and 4.0, respectively) have been identified, suggesting that the remaining heritability is likely to be explained by the cumulative effect of such alleles and/or by rare high-penetrance alleles. Relatively few studies have specifically explored the mitochondrial genome for variants potentially implicated in breast cancer risk. For these reasons, we propose an exploration of the variability of the mitochondrial genome in individuals diagnosed with breast cancer, having a positive breast cancer family history but testing negative for BRCA1/2 pathogenic mutations. We sequenced the mitochondrial genome of 436 index breast cancer cases from the GENESIS study. As expected, no pathogenic genomic pattern common to the 436 women included in our study was observed. The mitochondrial genes MT-ATP6 and MT-CYB were observed to carry the highest number of variants in the study. The proteins encoded by these genes are involved in the structure of the mitochondrial respiration chain, and variants in these genes may impact reactive oxygen species production contributing to carcinogenesis. More functional and epidemiological studies are needed to further investigate to what extent variants identified may influence familial breast cancer risk.

Mutation screening of MIR146A/B and BRCA1/2 3′-UTRs in the GENESIS study

Although a wide number of breast cancer susceptibility alleles associated with various levels of risk have been identified to date, about 50% of the heritability is still missing. Although the major BRCA1 and BRCA2 genes are being extensively screened for truncating and missense variants in breast and/or ovarian cancer families, potential regulatory variants affecting their expression remain largely unexplored. In an attempt to identify such variants, we focused our attention on gene regulation mediated by microRNAs (miRs). We screened two genes, MIR146A and MIR146B, producing miR-146a and miR-146b-5p, respectively, that regulate BRCA1, and the 3′- untranslated regions (3′-UTRs) of BRCA1 and BRCA2 in the GENESIS French national case/control study (BRCA1- and BRCA2-negative breast cancer cases with at least one sister with breast cancer and matched controls). We identified one rare variant in MIR146A, four in MIR146B, five in BRCA1 3′-UTR and one in BRCA2 3′-UTR in 716 index cases and 619 controls. Among these 11 rare variants, 7 were identified each in 1 index case. None of the three relevant MIR146A/MIR146B variants affected the pre-miR sequences. The potential causality of the four relevant BRCA1/BRCA2 3′-UTRs variants was evaluated with luciferase reporter assays and co-segregation studies, as well as with bioinformatics analyses to predict miRs-binding sites, RNA secondary structures and RNA accessibility. This is the first study to report the screening of miR genes and of BRCA2 3′-UTR in a large series of familial breast cancer cases. None of the variant identified in this study gave convincing evidence of potential pathogenicity.

Familial breast cancer and DNA repair genes: insights into known and novel susceptibility genes from the GENESIS study, and implications for multigene panel testing: Contribution of DNA repair genes in familial breast cancer

Pathogenic variants in BRCA1 and BRCA2 only explain the underlying genetic cause of about 10% of hereditary breast and ovarian cancer families. Because of cost‐effectiveness, multigene panel testing is often performed even if the clinical utility of testing most of the genes remains questionable. The purpose of our study was to assess the contribution of rare, deleterious‐predicted variants in DNA repair genes in familial breast cancer (BC) in a well‐characterized and homogeneous population. We analyzed 113 DNA repair genes selected from either an exome sequencing or a candidate gene approach in the GENESIS study, which includes familial BC cases with no BRCA1 or BRCA2 mutation and having a sister with BC (N = 1,207), and general population controls (N = 1,199). Sequencing data were filtered for rare loss‐of‐function variants (LoF) and likely deleterious missense variants (MV). We confirmed associations between LoF and MV in PALB2, ATM and CHEK2 and BC occurrence. We also identified for the first time associations between FANCI, MAST1, POLH and RTEL1 and BC susceptibility. Unlike other associated genes, carriers of an ATM LoF had a significantly higher risk of developing BC than carriers of an ATM MV (ORLoF = 17.4 vs. ORMV = 1.6; p Het = 0.002). Hence, our approach allowed us to specify BC relative risks associated with deleterious‐predicted variants in PALB2, ATM and CHEK2 and to add MAST1, POLH, RTEL1 and FANCI to the list of DNA repair genes possibly involved in BC susceptibility. We also highlight that different types of variants within the same gene can lead to different risk estimates.

GEMO, a national resource to study genetic modifiers of breast and ovarian cancer risk in BRCA1 and BRCA2 pathogenic variant carriers

Women carrying a pathogenic variant (PV) in the BRCA1 or BRCA2 (BRCA1/2) genes are at high lifetime risk of developing breast cancer (BC) and ovarian cancer (OC), but estimation of the cumulative risk of cancer to age 70 years varies substantially between studies and populations. Initial estimations were obtained from selected high-risk families with multiple cases, such as those ascertained through the Breast Cancer Linkage Consortium used to identify disease loci (1). In the first retrospective studies conducted on such families, estimates for BC ranged from 40 to 87% for BRCA1 PV carriers and from 27 to 84% for BRCA2 PV carriers and estimates for OC ranged from 16 to 68% for BRCA1 PV carriers and from 11 to 27% for BRCA2 PV carriers (1–4). Recently, the largest prospective cohort conducted to date reported cumulative risks of BC to age 80 years of 72% for BRCA1 PV carriers and 69% for BRCA2 PV carriers (5). In the same study, cumulative risks of OC to age 80 years were 44% for BRCA1 PV carriers and 17% for BRCA2 PV carriers. Variation in cancer risks within or between BRCA1/2 families, with respect to age at diagnosis or type of cancer, can be explained by other genetic factors and/or lifestyle and reproductive factors (6–10). Genome-wide association studies (GWAS) conducted by the Breast Cancer Association Consortium (BCAC) have identified 172 common single-nucleotide polymorphisms (SNPs) associated with small increases in breast and/or ovarian cancer risk in the general population (11). A subset of these SNPs modifies the risk of breast and ovarian cancer risk for BRCA1/2 PV carriers (12–14) but most of the variability has not been explained yet (15). Breast and ovarian cancer risks in BRCA1/2 PV carriers might also vary according to the location of the variant and/or its origin (14, 16–19). Genetic testing for BRCA1 and BRCA2 has been part of genetic counseling in European Union countries and North America since their discovery in the 90s, and has greatly improved recommendations about clinical management options and the most appropriate treatments. Nonetheless, both retrospective and prospective studies on large datasets of BRCA1/2 PV carrier families are still very much needed to refine individual cancer risk estimates by considering other genetic and lifestyle/environmental factors, and they will also contribute to a better understanding of the correlation between mutant BRCA1/2 alleles and phenotype. In particular, accurate age-specific risk estimates for the different types of cancer would be useful when choosing risk reduction strategies such as prophylactic bilateral mastectomy or salphingo-oophorectomy. The Genetic Modifiers of BRCA1 and BRCA2 (GEMO) Group is the French multidisciplinary, collaborative framework for the investigation of genetic factors modifying cancer risk in Hereditary Breast and Ovarian cancer (HBOC) families segregating BRCA1/2 PVs. Its primary aims are to contribute to large-scale national and international projects to identify genetic modifiers and to facilitate the translation of research results to the clinical setting. This is achieved by establishing a resource of blood DNA samples from individuals carrying a PV together with family and clinical data through the nation-wide network of cancer genetic clinics. Here we report on the progress of the GEMO study, the characteristics of the 5,303 actual participants and the prevalence and spectrum of BRCA1/2 cancer-associated variants identified so far.