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 Huntington's 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).

GENESIS: a French national resource to study the missing heritability of breast cancer.

BACKGROUND: Less than 20% of familial breast cancer patients who undergo genetic testing for BRCA1 and BRCA2 carry a pathogenic mutation in one of these two genes. The GENESIS (GENE SISter) study was designed to identify new breast cancer susceptibility genes in women attending cancer genetics clinics and with no BRCA1/2 mutation. METHODS: The study involved the French national network of family cancer clinics. It was based on enrichment in genetic factors of the recruited population through case selection relying on familial criteria, but also on the consideration of environmental factors and endophenotypes like mammary density or tumor characteristics to assess potential genetic heterogeneity. One of the initial aims of GENESIS was to recruit affected sibpairs. Siblings were eligible when index cases and at least one affected sister were diagnosed with infiltrating mammary or ductal adenocarcinoma, with no BRCA1/2 mutation. In addition, unrelated controls and unaffected sisters were recruited. The enrolment of patients, their relatives and their controls, the collection of the clinical, epidemiological, familial and biological data were centralized by a coordinating center. RESULTS: Inclusion of participants started in February 2007 and ended in December 2013. A total of 1721 index cases, 826 affected sisters, 599 unaffected sisters and 1419 controls were included. 98% of participants completed the epidemiological questionnaire, 97% provided a blood sample, and 76% were able to provide mammograms. Index cases were on average 59 years old at inclusion, were born in 1950, and were 49.7 years of age at breast cancer diagnosis. The mean age at diagnosis of affected sisters was slightly higher (51.4 years). The representativeness of the control group was verified. CONCLUSIONS: The size of the study, the availability of biological specimens and the clinical data collection together with the detailed and complete epidemiological questionnaire make this a unique national resource for investigation of the missing heritability of breast cancer, by taking into account environmental and life style factors and stratifying data on endophenotypes to decrease genetic heterogeneity.

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.

Mutation analysis of PALB2 gene in French breast cancer families.

Several population-based and family-based studies have demonstrated that germline mutations of the PALB2 gene (Partner and Localizer of BRCA2) are associated with an increased risk of breast cancer. Distinct mutation frequencies and spectrums have been described depending on the population studied. Here we describe the first complete PALB2 coding sequence screening in the French population. We screened the complete coding sequence and intron-exon boundaries of PALB2, using the EMMA technique, to assess the contribution of pathogenic mutations in a set of 835 familial breast cancer cases and 662 unrelated controls from the French national study GENESIS and the Paul Strauss Cancer Centre, all previously tested negative for BRCA1 and BRCA2 pathogenic mutations. Our analysis revealed the presence of four novel deleterious mutations: c.1186insT, c.1857delT and c.2850delC in three cases, c.3418dupT in one control. In addition, we identified two in-frame insertion/deletion, 19 missense substitutions (two of them predicted as pathogenic), 9 synonymous variants, 28 variants located in introns and 2 in UTRs, as well as frequent variants. Truncating PALB2 mutations were found in 0.36% of familial breast cancer cases, a frequency lower than the one detected in comparable studies in other populations (0.73-3.40%). This suggests a small but significant contribution of PALB2 mutations to the breast cancer susceptibility in the French population.

FANCM c.5791C>T nonsense mutation (rs144567652) induces exon skipping, affects DNA repair activity and is a familial breast cancer risk factor.

Numerous genetic factors that influence breast cancer risk are known. However, approximately two-thirds of the overall familial risk remain unexplained. To determine whether some of the missing heritability is due to rare variants conferring high to moderate risk, we tested for an association between the c.5791C>T nonsense mutation (p.Arg1931*; rs144567652) in exon 22 of FANCM gene and breast cancer. An analysis of genotyping data from 8635 familial breast cancer cases and 6625 controls from different countries yielded an association between the c.5791C>T mutation and breast cancer risk [odds ratio (OR) = 3.93 (95% confidence interval (CI) = 1.28-12.11; P = 0.017)]. Moreover, we performed two meta-analyses of studies from countries with carriers in both cases and controls and of all available data. These analyses showed breast cancer associations with OR = 3.67 (95% CI = 1.04-12.87; P = 0.043) and OR = 3.33 (95% CI = 1.09-13.62; P = 0.032), respectively. Based on information theory-based prediction, we established that the mutation caused an out-of-frame deletion of exon 22, due to the creation of a binding site for the pre-mRNA processing protein hnRNP A1. Furthermore, genetic complementation analyses showed that the mutation influenced the DNA repair activity of the FANCM protein. In summary, we provide evidence for the first time showing that the common p.Arg1931* loss-of-function variant in FANCM is a risk factor for familial breast cancer.