Detection of Folliculin Gene Mutations in Two Chinese Families with Birt-Hogg-Dube Syndrome.
ABSTRACT: Birt-Hogg-Dube syndrome (BHD, OMIM#135150) is a rare disease in clinic; it is characterized by skin fibrofolliculomas, pulmonary cysts with an increased risk of recurrent pneumothorax, renal cysts, and renal neoplasms. Previous studies have demonstrated that variants in folliculin (FLCN, NM_144997) are mainly responsible for this disease. In this research, we enrolled two BHD families and applied direct sequencing of FLCN to explore the genetic lesions in them. Two FLCN mutations were identified: one is a novel deletion variant (c.668delA/p.N223TfsX19), while the other is a previously reported insertion mutation (c.1579_1580insA/p.R527QfsX75). And the pathogenicity of both variants was confirmed by cosegregation assay. Bioinformatics analysis showed that c.668delA may lead to functional haploinsufficiency of FLCN because mRNA carrying this mutation exhibits a faster degradation rate comparing to the wild type. Real-time qPCR also confirmed that the mRNA level of FLCN expression in the proband was decreased significantly compared with the controls, which may disrupt the mTOR pathway and lead to BHD. The insertion mutation (c.1579_1580insA) was predicted to cause a prolonged amino acid sequence of FLCN. The present identification of two mutations not only further supports the important role of tumor suppressor FLCN in BHD and primary spontaneous pneumothorax, but also expands the spectrum of FLCN mutations and will provide insight into genetic diagnosis and counseling of families with BHD.
Project description:BACKGROUND: Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominantly inherited disorder caused by germline mutations in the folliculin (FLCN) gene. Clinical manifestations of BHD include skin fibrofolliculomas, renal cell cancer, lung cysts and (recurrent) spontaneous pneumothorax (SP). All clinical manifestations usually present in adults > 20 years of age. CASE PRESENTATIONS: Two non-related patients with (recurrent) pneumothorax starting at age 14 accompanied by multiple basal lung cysts on thoracic CT underwent FLCN germline mutation analysis. A pathogenic FLCN mutation was found in both patients confirming suspected BHD. The family history was negative for spontaneous pneumothorax in both families. CONCLUSION: Although childhood occurrence of SP in BHD is rare, these two cases illustrate that BHD should be considered as cause of SP in children.
Project description:Birt-Hogg-Dubé (BHD) syndrome, a hereditary renal cancer syndrome caused by mutations in the folliculin (FLCN) gene, is characterized by the presence of fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cell carcinoma (RCC). Few BHD syndrome cases have been reported in Asian countries, and cutaneous presentations are relatively rare in Asian patients. Asian BHD patients may be misdiagnosed due to their atypical manifestations. Here, we report two Chinese BHD patients with novel FLCN mutations (c.946-947delAG in exon 9 and c.770-772delCCT in exon 7). Both of them had RCC and spontaneous pneumothorax without fibrofolliculomas. In patients with RCC and pulmonary cysts but without cutaneous lesions, screening for mutations in the FLCN gene should be performed, especially for those with a family history of RCC or pulmonary cysts (pneumothorax).
Project description:Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant inherited disorder characterised by fibrofolliculomas, renal tumours, pulmonary cysts and pneumothorax. The pulmonary cysts and repeated episodes of pneumothorax are the clinical hallmarks for discovering families affected by the syndrome. This disorder is caused by mutations in the gene coding for folliculin (FLCN). FLCN forms a complex with FLCN-interacting protein 1 (FNIP1) and FNIP2 (also known as FNIPL), and the complex cross-talks with signalling molecules such as 5'-AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR). Heterozygous Flcn knockout mice and rats with Flcn gene mutations develop renal cysts, adenomas and/or carcinomas. These findings suggest that FLCN functions as a tumour suppressor that inhibits renal carcinogenesis. However, the mechanisms of the formation of pulmonary cysts and pneumothorax associated with heterozygous mutations in FLCN are poorly understood. Resected lung specimens from patients with BHD are often misdiagnosed by pathologists as non-specific blebs or bullae or emphysema, and patients with BHD who have pulmonary cysts and repeated pneumothorax frequently do not receive appropriate medical investigations. This review discusses the clinical and pathological features of lungs of patients with BHD, focusing on the diagnostic pathology and possible mechanisms of cyst formation.
Project description:Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant disorder, the main manifestations of which are fibrofolliculomas, renal tumors, pulmonary cysts and recurrent pneumothorax. The known causative gene for BHD syndrome is the folliculin (FLCN) gene on chromosome 17p11.2. Studies of the FLCN mutation for BHD syndrome are less prevalent in Chinese populations than in Caucasian populations. Our study aims to investigate the genotype spectrum in a group of Chinese patients with BHD.We enrolled 51 patients with symptoms highly suggestive of BHD from January 2014 to February 2017. The FLCN gene was examined using PCR and Sanger sequencing in every patient, for those whose Sanger sequencing showed negative mutation results, multiplex ligation-dependent probe amplification (MLPA) testing was conducted to detect any losses of large segments.Among the 51 patients, 27 had FLCN germline mutations. In total, 20 mutations were identified: 14 were novel mutations, including 3 splice acceptor site mutations, 2 different deletions, 6 nonsense mutations, 1 missense mutation, 1 small insertion, and 1 deletion of the whole exon 8.We found a similar genotype spectrum but different mutant loci in Chinese patients with BHD compared with European and American patients, thus providing stronger evidence for the clinical molecular diagnosis of BHD in China. It suggests that mutation analysis of the FLCN gene should be systematically conducted in patients with cystic lung diseases.
Project description:BACKGROUND:Familial spontaneous pneumothorax (FSP) is an inherited disease, and Birt-Hogg-Dubé (BHD) syndrome is its leading cause. BHD syndrome is an autosomal dominant disorder characterized by pulmonary cysts, spontaneous pneumothorax, renal cancer, and skin fibrofolliculomas. It is caused by germline mutations in the FLCN gene. Thus far a variety of mutations have been reported; however, the unique characteristics of BHD syndrome-related FSP are still unclear. METHOD:We reviewed the family history of a large Chinese family that presented with FSP. Genetic testing of the FLCN gene was performed and the special clinical characteristics of BHD syndrome-related FSP were discussed. RESULTS:This family comprised 5 generations and 76 members. Six of these had experienced pneumothorax episodes and 35 members had undergone genetic analysis of the FLCN gene, except for one member who had pneumothorax. Among the 35 members, 17 had the mutation in the FLCN gene. All five members with pneumothorax had the mutation. Frequency of pneumothorax in the mutation members was 29.4% (5/17). Clinical characteristics of the BHD syndrome-related pneumothorax differed from those of primary spontaneous pneumothorax, which typically affects tall, thin young men, and the recurrence rate of BHD syndrome-related pneumothorax after observation, needle aspiration or tube drainage was higher than that of primary spontaneous pneumothorax, and higher than that observed after VATS bullectomy and mechanical pleurodesis. CONCLUSIONS:We reported the largest single family that presented with FSP from China. The clinical and genetic characteristics of the BHD syndrome-related pneumothorax differ from those of primary spontaneous pneumothorax.
Project description:Birt-Hogg-Dubé syndrome (BHD) is a dominantly inherited familial cancer syndrome characterised by the development of benign skin fibrofolliculomas, multiple lung and kidney cysts, spontaneous pneumothorax and susceptibility to renal cell carcinoma. BHD is caused by mutations in the gene encoding Folliculin (FLCN). Little is known about what FLCN does in a healthy individual and how best to treat those with BHD. As a first approach to developing a vertebrate model for BHD we aimed to identify the temporal and spatial expression of flcn transcripts in the developing zebrafish embryo. To gain insights into the function of flcn in a whole organism system we generated a loss of function model of flcn by the use of morpholino knockdown in zebrafish.flcn is expressed broadly and upregulated in the fin bud, somites, eye and proliferative regions of the brain of the Long-pec stage zebrafish embryos. Together with knockdown phenotypes, expression analysis suggest involvement of flcn in zebrafish embryonic brain development. We have utilised the zFucci system, an in vivo, whole organism cell cycle assay to study the potential role of flcn in brain development. We found that at the 18 somite stage there was a significant drop in cells in the S-M phase of the cell cycle in flcn morpholino injected embryos with a corresponding increase of cells in the G1 phase. This was particularly evident in the brain, retina and somites of the embryo. Timelapse analysis of the head region of flcn morpholino injected and mismatch control embryos shows the temporal dynamics of cell cycle misregulation during development.In conclusion we show that zebrafish flcn is expressed in a non-uniform manner and is likely required for the maintenance of correct cell cycle regulation during embryonic development. We demonstrate the utilisation of the zFucci system in testing the role of flcn in cell proliferation and suggest a function for flcn in regulating cell proliferation in vertebrate embryonic brain development.
Project description:The Birt-Hogg-Dubé (BHD) syndrome is a very rare autosomal dominant form of genodermatosis caused by germline mutations in the folliculin (FLCN) gene, which is mapped to the p11.2 region in chromosome 17. BHD commonly presents cutaneous fibrofolliculomas, pulmonary cysts, renal cell carcinoma, and recurrent pneumothoraxes. The disease is easily ignored or misdiagnosed as pneumothorax, pulmonary lymphangiomyomatosis (LAM), or emphysema. Follow-up and guidelines for managing recurrent pneumothoraxes in these patients are lacking.We reported the case of a 56-year-old Chinese woman who presented skin lesions, multiple lung bubblae, recurrent pneumothoraxes, thyroid nodules, and pulmonary inflammatory pseudotumors (PITs). The patient had a family history of pneumothoraxes and renal tumor. The BHD diagnosis was confirmed by genetic testing, which revealed a novel FLCN mutation in exon 14. Furthermore, the patient underwent a bullectomy because of recurrent pneumothorax 6 years ago.To our knowledge, the novel mutation in exon 14 and the manifestation of PIT in the present case have never been reported for BHD. The patient underwent a bullectomy previously with no relapse at the last follow-up before the preparation of this report, thereby suggesting that thoracotomy with bullectomy may be a possible therapeutic approach for some BHD patients with recurrent pneumothorax.
Project description:BACKGROUND: Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant condition caused by germline FLCN mutations, and characterised by fibrofolliculomas, pneumothorax and renal cancer. The renal cancer risk, cancer phenotype and pneumothorax risk of BHD have not yet been fully clarified. The main focus of this study was to assess the risk of renal cancer, the histological subtypes of renal tumours and the pneumothorax risk in BHD. METHODS: In this study we present the clinical data of 115 FLCN mutation carriers from 35 BHD families. RESULTS: Among 14 FLCN mutation carriers who developed renal cancer 7 were <50 years at onset and/or had multifocal/bilateral tumours. Five symptomatic patients developed metastatic disease. Two early-stage cases were diagnosed by surveillance. The majority of tumours showed characteristics of both eosinophilic variants of clear cell and chromophobe carcinoma. The estimated penetrance for renal cancer and pneumothorax was 16% (95% minimal confidence interval: 6-26%) and 29% (95% minimal confidence interval: 9-49%) at 70 years of age, respectively. The most frequent diagnosis in families without identified FLCN mutations was familial multiple discoid fibromas. CONCLUSION: We confirmed a high yield of FLCN mutations in clinically defined BHD families, we found a substantially increased lifetime risk of renal cancer of 16% for FLCN mutation carriers. The tumours were metastatic in 5 out of 14 patients and tumour histology was not specific for BHD. We found a pneumothorax risk of 29%. We discuss the implications of our findings for diagnosis and management of BHD.
Project description:Germline mutations in the novel tumor suppressor gene FLCN are responsible for the autosomal dominant inherited disorder Birt-Hogg-Dubé (BHD) syndrome that predisposes to fibrofolliculomas, lung cysts and spontaneous pneumothorax, and an increased risk for developing kidney tumors. Although the encoded protein, folliculin (FLCN), has no sequence homology to known functional domains, x-ray crystallographic studies have shown that the C-terminus of FLCN has structural similarity to DENN (differentially expressed in normal cells and neoplasia) domain proteins that act as guanine nucleotide exchange factors (GEFs) for small Rab GTPases. FLCN forms a complex with folliculin interacting proteins 1 and 2 (FNIP1, FNIP2) and with 5' AMP-activated protein kinase (AMPK). This review summarizes FLCN functional studies which support a role for FLCN in diverse metabolic pathways and cellular processes that include modulation of the mTOR pathway, regulation of PGC1? and mitochondrial biogenesis, cell-cell adhesion and RhoA signaling, control of TFE3/TFEB transcriptional activity, amino acid-dependent activation of mTORC1 on lysosomes through Rag GTPases, and regulation of autophagy. Ongoing research efforts are focused on clarifying the primary FLCN-associated pathway(s) that drives the development of fibrofolliculomas, lung cysts and kidney tumors in BHD patients carrying germline FLCN mutations.
Project description:Birt-Hogg-Dubé (BHD) syndrome is a cancer disorder caused by a pathogenic FLCN mutation characterized by fibrofolliculomas, lung cysts, pneumothorax, benign renal cyst, and renal cell carcinoma (RCC). In this case we describe a patient with bilateral renal tumour and a positive familial history for pneumothorax and renal cancer. Based on this clinical presentation, the patient was suspected for BHD syndrome, which was confirmed after molecular testing. We discuss the importance of recognizing this autosomal dominant cancer disorder when a patient is presented at the urologist with a positive family history of chromophobe renal cell cancer or a positive familial history for renal cell cancer and pneumothorax.