Genetic screening of the FLCN gene identify six novel variants and a Danish founder mutation.

Pathogenic germline mutations in the folliculin (FLCN) tumor suppressor gene predispose to Birt-Hogg-Dubé (BHD) syndrome, a rare disease characterized by the development of cutaneous hamartomas (fibrofolliculomas), multiple lung cysts, spontaneous pneumothoraces and renal cell cancer. In this study, we report the identification of 13 variants and three polymorphisms in the FLCN gene in 143 Danish patients or families with suspected BHD syndrome. Functional mini-gene splicing analysis revealed that two intronic variants (c.1062+2T>G and c.1177-5_1177-3del) introduced splicing aberrations. Eleven families exhibited the c.1062+2T>G mutation. Combined single nucleotide polymorphism array-haplotype analysis showed that these families share a 3-Mb genomic fragment containing the FLCN gene, revealing that the c.1062+2T>G mutation is a Danish founder mutation. On the basis of in silico prediction and functional splicing assays, we classify the 16 identified variants in the FLCN gene as follows: nine as pathogenic, one as likely pathogenic, three as likely benign and three as polymorphisms. In conclusion, the study describes the FLCN mutation spectrum in Danish BHD patients, and contributes to a better understanding of BHD syndrome and management of BHD patients.

An original phylogenetic approach identified mitochondrial haplogroup T1a1 as inversely associated with breast cancer risk in BRCA2 mutation carriers.

INTRODUCTION: Individuals carrying pathogenic mutations in the BRCA1 and BRCA2 genes have a high lifetime risk of breast cancer. BRCA1 and BRCA2 are involved in DNA double-strand break repair, DNA alterations that can be caused by exposure to reactive oxygen species, a main source of which are mitochondria. Mitochondrial genome variations affect electron transport chain efficiency and reactive oxygen species production. Individuals with different mitochondrial haplogroups differ in their metabolism and sensitivity to oxidative stress. Variability in mitochondrial genetic background can alter reactive oxygen species production, leading to cancer risk. In the present study, we tested the hypothesis that mitochondrial haplogroups modify breast cancer risk in BRCA1/2 mutation carriers. METHODS: We genotyped 22,214 (11,421 affected, 10,793 unaffected) mutation carriers belonging to the Consortium of Investigators of Modifiers of BRCA1/2 for 129 mitochondrial polymorphisms using the iCOGS array. Haplogroup inference and association detection were performed using a phylogenetic approach. ALTree was applied to explore the reference mitochondrial evolutionary tree and detect subclades enriched in affected or unaffected individuals. RESULTS: We discovered that subclade T1a1 was depleted in affected BRCA2 mutation carriers compared with the rest of clade T (hazard ratio (HR) = 0.55; 95% confidence interval (CI), 0.34 to 0.88; P = 0.01). Compared with the most frequent haplogroup in the general population (that is, H and T clades), the T1a1 haplogroup has a HR of 0.62 (95% CI, 0.40 to 0.95; P = 0.03). We also identified three potential susceptibility loci, including G13708A/rs28359178, which has demonstrated an inverse association with familial breast cancer risk. CONCLUSIONS: This study illustrates how original approaches such as the phylogeny-based method we used can empower classical molecular epidemiological studies aimed at identifying association or risk modification effects.

COMPLEXO: identifying the missing heritability of breast cancer via next generation collaboration.

Linkage analysis, positional cloning, candidate gene mutation scanning and genome-wide association study approaches have all contributed significantly to our understanding of the underlying genetic architecture of breast cancer. Taken together, these approaches have identified genetic variation that explains approximately 30% of the overall familial risk of breast cancer, implying that more, and likely rarer, genetic susceptibility alleles remain to be discovered.

Common breast cancer susceptibility alleles are associated with tumour subtypes in BRCA1 and BRCA2 mutation carriers: results from the Consortium of Investigators of Modifiers of BRCA1/2.

INTRODUCTION: Previous studies have demonstrated that common breast cancer susceptibility alleles are differentially associated with breast cancer risk for BRCA1 and/or BRCA2 mutation carriers. It is currently unknown how these alleles are associated with different breast cancer subtypes in BRCA1 and BRCA2 mutation carriers defined by estrogen (ER) or progesterone receptor (PR) status of the tumour. METHODS: We used genotype data on up to 11,421 BRCA1 and 7,080 BRCA2 carriers, of whom 4,310 had been affected with breast cancer and had information on either ER or PR status of the tumour, to assess the associations of 12 loci with breast cancer tumour characteristics. Associations were evaluated using a retrospective cohort approach. RESULTS: The results suggested stronger associations with ER-positive breast cancer than ER-negative for 11 loci in both BRCA1 and BRCA2 carriers. Among BRCA1 carriers, single nucleotide polymorphism (SNP) rs2981582 (FGFR2) exhibited the biggest difference based on ER status (per-allele hazard ratio (HR) for ER-positive = 1.35, 95% CI: 1.17 to 1.56 vs HR = 0.91, 95% CI: 0.85 to 0.98 for ER-negative, P-heterogeneity = 6.5 × 10-6). In contrast, SNP rs2046210 at 6q25.1 near ESR1 was primarily associated with ER-negative breast cancer risk for both BRCA1 and BRCA2 carriers. In BRCA2 carriers, SNPs in FGFR2, TOX3, LSP1, SLC4A7/NEK10, 5p12, 2q35, and 1p11.2 were significantly associated with ER-positive but not ER-negative disease. Similar results were observed when differentiating breast cancer cases by PR status. CONCLUSIONS: The associations of the 12 SNPs with risk for BRCA1 and BRCA2 carriers differ by ER-positive or ER-negative breast cancer status. The apparent differences in SNP associations between BRCA1 and BRCA2 carriers, and non-carriers, may be explicable by differences in the prevalence of tumour subtypes. As more risk modifying variants are identified, incorporating these associations into breast cancer subtype-specific risk models may improve clinical management for mutation carriers.

Birt-Hogg-Dubé syndrome: diagnosis and management.

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant condition characterised clinically by skin fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cancer. The condition is caused by germline mutations in the FLCN gene, which encodes folliculin; the function of this protein is largely unknown, although FLCN has been linked to the mTOR pathway. The availability of DNA-based diagnosis has allowed insight into the great variation in expression of FLCN, both within and between families. Patients can present with skin signs and also with pneumothorax or renal cancer. Preventive measures are aimed mainly at early diagnosis and treatment of renal cancer. This Review gives an overview of current diagnosis and management of BHD.

Functional characterization of BRCA1 gene variants by mini-gene splicing assay.

Mutational screening of the breast cancer susceptibility gene BRCA1 leads to the identification of numerous pathogenic variants such as frameshift and nonsense variants, as well as large genomic rearrangements. The screening moreover identifies a large number of variants, for example, missense, silent, and intron variants, which are classified as variants of unknown clinical significance owing to the lack of causal evidence. Variants of unknown clinical significance can potentially have an impact on splicing and therefore functional examinations are warranted to classify whether these variants are pathogenic or benign. Here we validate a mini-gene splicing assay by comparing the results of 24 variants with previously published data from RT-PCR analysis on RNA from blood samples/lymphoblastoid cell lines. The analysis showed an overall concordance of 100%. In addition, we investigated 13 BRCA1 variants of unknown clinical significance or putative variants affecting splicing by in silico analysis and mini-gene splicing assay. Both the in silico analysis and mini-gene splicing assay classified six BRCA1 variants as pathogenic (c.80+1G>A, c.132C>T (p.=), c.213-1G>A, c.670+1delG, c.4185+1G>A, and c.5075-1G>C), whereas six BRCA1 variants were classified as neutral (c.-19-22_-19-21dupAT, c.302-15C>G, c.547+14delG, c.4676-20A>G, c.4987-21G>T, and c.5278-14C>G) and one BRCA1 variant remained unclassified (c.670+16G>A). In conclusion, our study emphasizes that in silico analysis and mini-gene splicing assays are important for the classification of variants, especially if no RNA is available from the patient. This knowledge is crucial for proper genetic counseling of patients and their family members.

Molecular composition of IMP1 ribonucleoprotein granules.

Localized mRNAs are transported to sites of local protein synthesis in large ribonucleoprotein (RNP) granules, but their molecular composition is incompletely understood. Insulin-like growth factor II mRNA-binding protein (IMP) zip code-binding proteins participate in mRNA localization, and in motile cells IMP-containing granules are dispersed around the nucleus and in cellular protrusions. We isolated the IMP1-containing RNP granules and found that they represent a unique RNP entity distinct from neuronal hStaufen and/or fragile X mental retardation protein granules, processing bodies, and stress granules. Granules were 100-300 nm in diameter and consisted of IMPs, 40 S ribosomal subunits, shuttling heterologous nuclear RNPs, poly(A)-binding proteins, and mRNAs. Moreover granules contained CBP80 and factors belonging to the exon junction complex and lacked eIF4E, eIF4G, and 60 S ribosomal subunits, indicating that embodied mRNAs are not translated. Granules embodied mRNAs corresponding to about 3% of the human embryonic kidney 293 mRNA transcriptome. Messenger RNAs encoding proteins participating in the secretory pathway and endoplasmic reticulum-associated quality control, as well as ubiquitin-dependent metabolism, were enriched in the granules, reinforcing the concept of RNP granules as post-transcriptional operons.