Birt-Hogg-Dubé syndrome: clinical and genetic studies of 10 French families

ERN GENTURIS clinical practice guidelines for the diagnosis, surveillance and management of people with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHD syndrome) is an autosomal dominant multisystem disorder with variable expression due to pathogenic constitutional variants in the FLCN gene. Patients with BHD syndrome are predisposed to benign cutaneous fibrofolliculomas/trichodischomas, pulmonary cysts with an associated risk of spontaneous pneumothorax, and renal cell carcinoma. A requirement for updated International consensus recommendations for the diagnosis and management of BHD syndrome was identified. Based on a comprehensive literature review and expert consensus within the fields of respiratory medicine, urology, radiology, dermatology, clinical oncology and clinical genetics, updated recommendations for diagnosis, surveillance and management in BHD syndrome were developed. With the widespread availability of FLCN genetic testing, clinical scenarios in which a diagnosis should be considered and criteria for genetic testing were defined. Following a clinical and/or molecular diagnosis of BHD syndrome, a multidisciplinary approach to disease management is required. Regular renal cancer surveillance is recommended in adulthood and life-long, but the evidence base for additional tumour surveillance is limited and further research warranted. Recommendations for the treatment of cutaneous, pulmonary and renal manifestations are provided. Awareness of BHD syndrome needs to be raised and better knowledge of the clinical settings in which the diagnosis should be considered should enable earlier diagnosis. Further details, including areas for future research topics are available at: https://www.genturis.eu/l=eng/Guidelines-and-pathways/Clinical-practice-guidelines.html .

A novel variant in the FLCN gene in a Chinese family with Birt-Hogg-Dubé syndrome

BACKGROUND

This study aimed to identify disease-causing variants within a Chinese family affected by Birt-Hogg-Dubé syndrome (BHDS), which arises from an autosomal dominant inheritance pattern attributed to variants in the folliculin (FLCN) gene, recognized as a tumor suppressor gene.

METHODS

A Chinese proband diagnosed with BHDS due to renal tumors underwent next-generation sequencing (NGS), revealing a novel variant in the FLCN gene. Sanger sequencing was subsequently performed on blood samples obtained from family members to confirm the presence of this variant.

RESULTS

A novel germline frameshift variant (NM_144997.5:c.977dup) was identified in five individuals among the screened family members, marking the first report of this variant. Additionally, a somatic frameshift variant (NM_144997.5:c.1252del) was detected in the renal tumors of the proband. No variant was detected in unaffected family members.

CONCLUSIONS

A novel heterozygous variant was identified in exon 9 of the FLCN gene, which broadens the spectrum of FLCN variants. We recommend that molecular analysis of the FLCN gene be performed in patients with suspected BHDS and their families.

A pathogenic variant in the FLCN gene presenting with pure dementia: is autophagy at the intersection between neurodegeneration and cancer?

Introduction

Folliculin, encoded by FLCN gene, plays a role in the mTORC1 autophagy cascade and its alterations are responsible for the Birt-Hogg-Dubé (BHD) syndrome, characterized by follicle hamartomas, kidney tumors and pneumothorax.

Patient and results

We report a 74-years-old woman diagnosed with dementia and carrying a FLCN alteration in absence of any sign of BHD. She also carried an alteration of MAT1A gene, which is also implicated in the regulation of mTORC1.

Discussion

The MAT1A variant could have prevented the development of a FLCN-related oncological phenotype. Conversely, our patient presented with dementia that, to date, has yet to be documented in BHD. Folliculin belongs to the DENN family proteins, which includes C9orf72 whose alteration has been associated to neurodegeneration. The folliculin perturbation could affect the C9orf72 activity and our patient could represent the first human model of a relationship between FLCN and C9orf72 across the path of autophagy.

[Genetic diffuse cystic lung disease in adults]

Multiple cystic lung diseases comprise a wide range of various diseases, some of them of genetic origin. Lymphangioleiomyomatosis (LAM) is a disease occurring almost exclusively in women, sporadically or in association with tuberous sclerosis complex (TSC). Patients with LAM present with lymphatic complications, renal angiomyolipomas and cystic lung disease responsible for spontaneous pneumothoraces and progressive respiratory insufficiency. TSC and LAM have been ascribed to mutations in TSC1 or TSC2 genes. Patients with TSC are variably affected by cutaneous, cognitive and neuropsychiatric manifestations, epilepsy, cerebral and renal tumors, usually of benign nature. Birt-Hogg-Dubé syndrome is caused by mutations in FLCN encoding folliculin. This syndrome includes lung cysts of basal predominance, cutaneous fibrofolliculomas and various renal tumors. The main complications are spontaneous pneumothoraces and renal tumors requiring systematic screening. The mammalian target of rapamycin (mTOR) pathway is involved in the pathophysiology of TSC, sporadic LAM and Birt-Hogg-Dubé syndrome. MTOR inhibitors are used in LAM and in TSC while Birt-Hogg-Dubé syndrome does not progress towards chronic respiratory failure. Future challenges in these often under-recognized diseases include the need to reduce the delay to diagnosis, and to develop potentially curative treatments. In France, physicians can seek help from the network of reference centers for the diagnosis and management of rare pulmonary diseases.

Clinical and genetic features of 334 Asian patients with Birt-Hogg-Dubé syndrome (BHDS) who presented with pulmonary cysts with or without a history of pneumothorax, with special reference to BHDS-associated pneumothorax

BACKGROUND

The clinical pulmonary manifestations and genetic features of Birt-Hogg-Dubé syndrome (BHDS) in Asian patients remained unclear. We aimed to clarify the clinical features of BHDS-associated pneumothorax (PTX) and retrospectively investigate potential contributing factors in the largest Asian cohort to date.

METHODS

We reviewed the clinical and genetic data collected in 2006-2017, from the BHDS patients who were Asian and presented with pulmonary cysts with or without a history of PTX.

RESULTS

Data from 334 (41.3% males; 58.7% females) patients from 297 unrelated families were reviewed. Among them, 314 (94.0%) patients developed PTX. The median age at the first occurrence of PTX was 32 years, which was significantly lower in males (P = 0.003) and patients without notable skin manifestations (P < 0.001). Seventy-six (24.2%) patients experienced their first PTX episode before the age of 25 years. PTX simultaneously occurred in the bilateral lungs of 37 (11.8%) patients. Among 149 patients who had their first PTX episode at least 10 years before BHDS diagnosis, PTX occurred more frequently in males (P = 0.030) and light smokers than in nonsmokers (P = 0.014). The occurrence of PTX peaked in the early 30s and gradually decreased with age but remained high in females (P = 0.001). We identified 70 unique FLCN germline variants, including duplications (46.4%), substitutions (7.1%), insertions/deletions (30.0%), and variants affecting splicing (12.5%). Approximately 80% of Asian patients suspected of having BHDS could be genetically diagnosed by examining FLCN exons 7, 9, 11, 12, and 13. No apparent genotype-phenotype correlation regarding pulmonary manifestations was identified.

CONCLUSIONS

Our findings indicate that sex, smoking history, and skin manifestations at BHDS diagnosis significantly influence the clinical features of BHDS-associated PTX. These findings may contribute to the appropriate management and treatment of BHDS-associated PTX.

Update of penetrance estimates in Birt-Hogg-Dubé syndrome

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare genetic syndrome caused by pathogenic or likely pathogenic germline variants in the FLCN gene. Patients with BHD syndrome have an increased risk of fibrofolliculomas, pulmonary cysts, pneumothorax and renal cell carcinoma. There is debate regarding whether colonic polyps should be added to the criteria. Previous risk estimates have mostly been based on small clinical case series.

METHODS

A comprehensive review was conducted to identify studies that had recruited families carrying pathogenic or likely pathogenic variants in FLCN. Pedigree data were requested from these studies and pooled. Segregation analysis was used to estimate the cumulative risk of each manifestation for carriers of FLCN pathogenic variants.

RESULTS

Our final dataset contained 204 families that were informative for at least one manifestation of BHD (67 families informative for skin manifestations, 63 for lung, 88 for renal carcinoma and 29 for polyps). By age 70 years, male carriers of the FLCN variant have an estimated 19% (95% CI 12% to 31%) risk of renal tumours, 87% (95% CI 80% to 92%) of lung involvement and 87% (95% CI 78% to 93%) of skin lesions, while female carriers had an estimated 21% (95% CI 13% to 32%) risk of renal tumours, 82% (95% CI 73% to 88%) of lung involvement and 78% (95% CI 67% to 85%) of skin lesions. The cumulative risk of colonic polyps by age 70 years old was 21% (95% CI 8% to 45%) for male carriers and 32% (95% CI 16% to 53%) for female carriers.

CONCLUSIONS

These updated penetrance estimates, based on a large number of families, are important for the genetic counselling and clinical management of BHD syndrome.

How New Developments Impact Diagnosis in Existing Renal Neoplasms

In recent years, several emerging diagnostic entities have been described in renal cell carcinoma (RCC). However, our understanding of well-known and established entities has also grown. Clear cell papillary RCC is now relabeled as a tumor rather than carcinoma in view of its nonaggressive behavior. Renal tumors with a predominantly infiltrative pattern are very important for recognition, as most of these have aggressive behavior, including fumarate hydratase-deficient RCC, SMARCB1-deficient medullary carcinoma, collecting duct carcinoma, urothelial carcinoma, and metastases from other cancers.

Birt-Hogg-Dubé syndrome: Another mTOR phenomenon

Birt-Hogg-Dubé syndrome is an uncommon autosomal dominant systemic disorder with cutaneous findings notable for fibrofolliculomas or trichodiscomas on the scalp, face, neck, and trunk. These cutaneous signs are associated with bilateral renal cell carcinoma, benign renal cysts, pulmonary cysts, and spontaneous pneumothorax. Given its autosomal dominant inheritance pattern, the successful diagnosis of Birt-Hogg-Dubé syndrome (BHDS) may elucidate a diagnosis in family members. BHDS results from a mutation in the FLCN gene encoding the folliculin protein, a transcriptional regulator of the mammalian target of rapamycin signaling pathway. Like tuberous sclerosis, BHDS's clinical features may subside with the use of oral rapamycin for mammalian target of rapamycin inhibition, a theoretical concept meriting exploration. Although its prevalence in the general population has been estimated at 2 cases per million, BHDS has been detected in a few patients from the nearby Portuguese-lineage quarter of the city of Newark, a disproportionate prevalence possibly explained by the founder effect.

Heterozygous germline FLCN mutation in Birt-Hogg-Dubé syndrome with bilateral renal hybrid oncocytic/chromophobe tumor and unilateral renal chromophobe cell carcinoma: a case report

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant tumor syndrome caused by Folliculin (FLCN) gene mutation. The clinical manifestations are diverse, and the renal tumor is the most serious.

CASE PRESENTATION

We report the case of a 51-year-old female with multiple space-occupying lesions in both kidneys, as well as bilateral renal cysts and multiple lung cysts. The resected tumors were finally diagnosed as bilateral renal hybrid oncocytic/chromophobe tumor (HOCT) and unilateral chromophobe cell carcinoma. A history of pneumothorax surgery 4 years ago was convinced. All of these strongly suggested the possibility of BHD syndrome. Gene test confirmed a heterozygous germline FLCN nonsense mutation (c.1429C > T, p.Arg477Ter). The patient is still doing well after 20 months of follow-up (cut-off date July 2022).

CONCLUSION

This is a case of BHD syndrome presented with bilateral renal tumor, renal cysts, and multiple lung cysts, and confirmed by gene testing. Patients with any combination of one or more of the manifestations should remain alert to the BHD syndrome. Our report will help to deepen the understanding of the clinicopathological features and molecular changes of BHD syndrome.

Birt-Hogg-Dubé syndrome in apparent primary spontaneous pneumothorax patients; results and recommendations for clinical practice

Background

Birt-Hogg-Dubé syndrome (BHD) is an inherited disease caused by pathogenic variants in the FLCN gene. One of the characteristics is the increased risk for spontaneous pneumothorax, likely due to the presence of pulmonary cysts mainly distributed under the carina. Due to variable expression and lack of awareness, BHD is likely to be underdiagnosed. We aimed to examine the prevalence of BHD in patients presenting with an apparent primary spontaneous pneumothorax and to evaluate the contribution of chest CT in establishing the diagnosis.

Methods

Patients who presented with apparent primary spontaneous pneumothorax between 2004 and 2017 in a large Dutch teaching hospital were enrolled in this quantitative cross-sectional study. A questionnaire was sent to eligible patients. Patients who completed the questionnaire and consented to further participation were invited to visit the hospital for genetic testing and low dose, volumetric chest CT.

Results

Genetic testing was performed in 88 patients with apparent primary spontaneous pneumothorax. Three patients were found to have a pathogenic variant in the FLCN gene (3.4%). No variants of unknown significance were detected. Pulmonary cysts were detected in 14 out of 83 participants with an available chest CT, six had more than one cyst. All three patients with BHD had multiple pulmonary cysts.

Conclusions

Based on previous literature and the present study, we believe that performing a chest CT in every patient presenting with primary spontaneous pneumothorax is justified. Subsequent genetic testing of the FLCN gene should be considered when multiple pulmonary cysts are present.

Trial registration

The study was registered at clinicaltrials.gov with reference NCT02916992.

Summary at a glance

Three out of 88 patients with an apparent primary spontaneous pneumothorax were diagnosed with Birt-Hogg-Dubé syndrome in this study and all three had multiple pulmonary cysts. We believe that performing a chest CT in every patient with an apparent primary spontaneous pneumothorax is justified to identify underlying diseases.

Adrenal Cortical Carcinoma and Additional Rare Pathologic Findings in Multi-Organs in a Birt-Hogg-Dubé Syndrome Patient: With an Emphasis on the Molecular Characteristics of Adrenal Cortical Carcinoma

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disorder caused by germline alterations in the FLCN gene. We report a 38-year-old man with BHD syndrome presenting with multiple rare pathologic findings involving various organs, including adrenal cortical carcinoma (ACC). Initially, he presented with severe cholestatic jaundice and was found to have a 25 cm left adrenal mass with radiologic evidence of lung metastases, which was diagnosed as ACC on resection. Concurrently, pigmented, bile-stained granular casts were present within the kidney and diffuse cholestasis of the liver consistent with Stauffer syndrome was identified. Subsequent staging workup detected a 1.2 cm tubulovillous adenoma in the distal ascending colon and an incidental 1.2 cm thyroid nodule. Germline genetic testing revealed a pathogenic FLCN c.1285dup. Targeted DNA next generation sequencing of ACC revealed FLCN c.1285dup, IDH2 c.5332C>T, PRKAR1A c.1074del, and PDGFRB c.3282C>A and concurrent transcriptomic analysis demonstrated VEGFA overexpression. Fourteen months after resection, follow-up computerized tomography (CT) identified the progression of lung metastases and chemotherapy with etoposide doxorubicin and cisplatin was initiated. Here, we report the first ACC with the molecular characteristics in a BHD syndrome patient, although 5 adrenal lesions, including ACC, adenomas or neoplasm with malignant potential due to higher Ki67 labelling index, have been reported in the literature and no somatic analysis in these tumors were performed. Despite the rarity, our case potentially expands the tumor spectrum of BHD patients, helps to solidify possible association with adrenal cortical tumors and reiterates the value of genetic counseling in patients with ACC.

Comment on Balsamo et al.: “Birt–Hogg–Dubé syndrome with simultaneous hyperplastic polyposis of the gastrointestinal tract: case report and review of the literature”

In this comment, we highlight the diagnosis of Birt–Hogg–Dubé (BHD) in a 60-year-old man was made from identification and removal of normochromic papular cutaneous lesions whose histological examination indicated trichodyscomas and which are considered equivalent to fibrofolliculomas, presence of bilateral renal mass suggestive of angiomyolipomas by imaging exams. A benign/likely benign variant of FLCN in the intron 13 was also detected. Still, his previous pathological history presented other relevant data such as the prior removal of vocal cord angioma, total thyroidectomy, and left parotidectomy due to a cystic lesion whose histopathological examination revealed the presence of oncocytoma and lipomatosis, in addition to basal cell cutaneous carcinoma. Simultaneous gastrointestinal hyperplastic polyposis was found in this patient. The case we reported does not have the genotypic and phenotypic expressions most present in BHDS. These facts make it important for readers to know the clinical and genetic presentation facets of this unusual syndrome.

Bibliometric Analysis of Birt-Hogg-Dubé Syndrome From 2001 to 2021

Background

Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominant inherited disorder caused by germline mutations in folliculin (FLCN). Despite our significantly evolved understanding of BHD over the past decades, no bibliometric analyses have been conducted in this field. This study aimed to analyze and visualize the characteristics of publication outputs, the research hotspots, and scientific frontiers about BHD using bibliometric analysis.

Methods

All relevant literature on BHD was culled from the Web of Science Core Collection (WoSCC) database. Valid data were extracted from the articles and visually analyzed using CiteSpace and VOSviewer.

Results

A total of 751 qualifying papers were included. Publication outputs concerning BHD increased over time. The dominant position of the United States and Japan in BHD research field was evident. National Cancer Institute (the USA) and Yokohama City University (Japan) were the two most productive organizations. W. Marston Linehan exerted a considerable publication impact and had made the most remarkable contributions in the field of BHD. Plos One was the journal with the highest publication outputs, and half of the top 10 journals and co-cited journals belonged to Q1 or Q2. Keyword citation bursts revealed that management, tumor suppressor, flcn gene, spectrum, diagnosis, risk, computed tomography were the emerging research hotspots.

Conclusion

Research on BHD is prosperous. International cooperation between countries and organizations is also expected to deepen and strengthen in the future. Our results indicated that FLCN-associated pathways involved in the pathogenesis of BHD, specific options for early diagnosis, and molecular-targeting therapies will remain research hotspots in the future.

A retrospective two centre study of Birt-Hogg-Dubé syndrome reveals a pathogenic founder mutation in FLCN in the Swedish population

Birt-Hogg-Dube syndrome (BHDS) (MIM: 135150) is a rare autosomal dominant disorder with variable penetrance, caused by pathogenic variants in the FLCN gene. Only a few hundreds of families have so far been described in the literature. Patients with BHDS present with three distinct symptoms: fibrofolliculomas, pneumothorax due to lung cyst formation, and increased lifetime risk of kidney tumours. The aim of the current study was to estimate the incidence of BHDS in the Swedish population and further describe the clinical manifestations and their frequency. Splice variant c.779+1G>T was the most common pathogenic variant, found in 57% of the families, suggesting this may be a founder mutation in the Swedish population. This was further investigated using haplotype analysis in 50 families that shared a common haplotype. Moreover, according to gnomAD the carrier frequency of the c.779+1G>T variant has been estimated to be 1/3265 in the Swedish population, however our data suggest that the carrier frequency in the Swedish population may be significantly higher. These findings should raise awareness among physicians of different specialties to patients presenting with fibrofolliculomas, pneumothorax and/or kidney tumours. We also stress the importance of consensus recommendations regarding diagnosis and clinical management of this, not that uncommon, syndrome.

A Unique Presentation of Birt-Hogg-Dube Syndrome

Birt-Hogg-Dube (BHD) syndrome is a rare autosomal dominant condition identified by the triad of cutaneous fibrofolliculomas, pulmonary cysts, and renal cell carcinoma. The vast majority of patients with BHD syndrome initially present with spontaneous pneumothorax. This unique case describes a patient with BHD syndrome who presented with sebaceous cysts and perifollicular fibromas. The evaluation by dermatology is what led to his diagnosis. Expanding the clinical presentation of BHD syndrome to encompass a variety of skin findings could help with recognizing these patients before they suffer the serious complications of renal carcinoma and pneumothorax.

A systematic review assessing the existence of pneumothorax-only variants of FLCN. Implications for lifelong surveillance of renal tumours

Individuals with Birt-Hogg-Dubé syndrome (BHDS) may develop fibrofolliculomas, pneumothorax and/or renal cell carcinoma (RCC). Currently, all patients with pathogenic FLCN variants are recommended to have renal surveillance. It has however been suggested that some FLCN variants only cause pneumothorax, which would make surveillance unnecessary in certain cases. This review assesses this possibility. We provide an up-to-date analysis of clinical and genetic features of BHDS. The PUBMED database was systematically searched to find all articles describing patients with pathogenic FLCN variants. The relevant clinical and genetic features of these patients were recorded and analysed. The prevalence of pneumothorax, pulmonary cysts, RCC and characteristic skin lesions in BHDS were 50.9% (n = 1038), 91.9% (n = 720), 22.5% (n = 929) and 47.9% (n = 989), respectively. There was a higher prevalence of pneumothoraces (p < 0.0001) but lower prevalence of dermatological findings (p < 0.0001) in patients from East Asia compared to North America or Europe. Of the 194 pathogenic FLCN variants, 76 could be defined as 'pneumothorax-only'. Pneumothorax only pathogenic variants (POPVs) were distributed throughout the gene, and there were no statistical differences in variant type. The majority of POPVs (65/76) affected no more than three individuals. Individuals with 'POPVs' also tended to be younger (45 vs. 47 years, p < 0.05). Many apparent POPVs in the literature could result from variable expressivity, age-related penetrance and other confounding factors. We therefore recommend that all individuals found to carry a pathogenic FLCN variant be enroled in lifelong surveillance for RCC.

Novel folliculin gene mutations in Polish patients with Birt-Hogg-Dubé syndrome

Background

Birt–Hogg–Dubé syndrome (BHDS) is a rare, autosomal dominant, inherited disease caused by mutations in the folliculin gene (FLCN). The disease is characterised by skin lesions (fibrofolliculomas, trichodiscomas, acrochordons), pulmonary cysts with pneumothoraces and renal tumours. We present the features of Polish patients with BHDS.

Materials and methods

The first case of BHDS in Poland was diagnosed in 2016. Since then, 15 cases from 10 families have been identified. Thirteen patients were confirmed via direct FLCN sequencing, and two according to their characteristic clinical and radiological presentations.

Results

BHDS was diagnosed in 15 cases (13 women and 2 men) from 10 families. The mean ages at the time of first pneumothorax and diagnosis were 38.4 ± 13.9 and 47.7 ± 13 years, respectively. Five patients (33%) were ex-smokers (2.1 ± 1.37 packyears), and 10 (67%) had never smoked cigarettes. Twelve patients (83%) had a history of recurrent symptomatic pneumothorax. Three patients had small, asymptomatic pneumothoraces, which were only detected upon computed tomography examination. All patients had multiple bilateral pulmonary cysts, distributed predominantly in the lower and middle, peripheral, and subpleural regions of the lungs. Generally, patients exhibited preserved lung function. Skin lesions were seen in four patients (27%), one patient had renal angiomyolipoma, and one had bilateral renal cancer. Different mutations of the FLCN gene were identified (mainly in exon 6), with two novel heterozygous variants: c.490delA p.(Arg164GlyTer13) and c.40delC p.(His14ThrsfTer41).

Conclusions

All analysed patients with BHDS presented with lung lesions and with less frequent skin and renal lesions than previously reported in other populations. In addition, more frequent mutations located in exon 6 were detected, and two novel FLCN gene mutations were identified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01931-0.

Familial spontaneous pneumothorax: importance of screening for Birt-Hogg-Dubé syndrome

OBJECTIVES

The goal of this study was to investigate the prevalence of Birt-Hogg-Dubé (BHD) syndrome in patients with familial spontaneous pneumothorax (FSP) and the clinical characteristics of pneumothorax related to BHD syndrome compared with those of primary spontaneous pneumothorax.

METHODS

A total of 37 families diagnosed with FSP from 2007 to 2017 were enrolled in this study. The FLCN gene, which is responsible for BHD syndrome, was sequenced using the Sanger method in 25 probands. For the patients with confirmed BHD syndrome-related pneumothorax, clinical characteristics including the median onset age of pneumothorax, the male-to-female ratio, the mean height and body mass index (BMI) and the recurrence rate after different treatment modalities were obtained and compared with those of patients with primary spontaneous pneumothorax.

RESULTS

Of the 25 probands with FSP, 16 [64.0%, 95% confidence interval (CI) 43.8-84.2%] harboured FLCN germline mutations. In the patients with BHD syndrome-related pneumothorax, the median onset age of pneumothorax was 34 years; the male-to-female ratio was 1.3:1; and the mean height and BMI were 167.0 ± 8.6 cm and 23.6 ± 3.4 kg/m2, respectively. These characteristics were significantly different from those in patients with primary spontaneous pneumothorax from the same centre. The recurrence rate of BHD syndrome-related pneumothorax after conservative therapy was 53.1% (95% CI 38.6-67.5%) compared with 9.1% (95% CI 0-19.4%) after surgical treatment.

CONCLUSIONS

BHD syndrome is one of the most common causes of FSP. Patients with FSP should be recommended for mutation screening for the FLCN gene to facilitate early diagnosis and proper intervention.

Prevalence of Birt-Hogg-Dubé Syndrome Determined Through Epidemiological Data on Spontaneous Pneumothorax and Bayes Theorem

Background: Birt-Hogg-Dubé syndrome (BHD) is a rare inherited disorder characterized by cutaneous fibrofolliculomas, multiple pulmonary cysts, recurrent spontaneous pneumothorax (SP), and renal tumors. More than 40 years after its description, the prevalence of BHD in the general population remains unknown. This study aimed at determining the prevalence of BHD by applying the Bayes theorem of conditional probability to epidemiological data on SP. Methods: We performed a meta-analysis of published data on: (1) the probability of having BHD among patients with apparent primary SP (4 studies), (2) the incidence rate of primary SP in the general population (9 studies), and (3) the probability of experiencing a SP in BHD (16 studies). Results were corrected for SP relapses, stratified by gender and year of study publication (before and after 2000), and computed with the Bayes equation. Results: The probability of having BHD among patients with apparent primary SP was 0.09 (95% confidence interval: 0.07, 0.11) or 9%. It was 0.20 (0.14, 0.27) in women and 0.05 (0.04, 0.07) in men. The incidence rate of primary SP in the general population was 8.69 (6.58, 11.46) per 100,000 person-years (p-y). It was 3.44 (2.36, 4.99) per 100,000 p-y in women and 13.96 (10.72, 18.18) per 100,000 p-y in men, and was about 2 times higher in studies published after 2000 than in those published before 2000. The probability of experiencing at least one SP among patients with BHD was 0.43 (0.31, 0.54) or 43%, without gender difference. By combining these data in the Bayes equation, we found a prevalence of BHD in the general population of 1.86 (1.16, 3.00) per million, with values of 1.86 (1.02, 3.39) per million in men, and 1.88 (0.97, 3.63) per million in women. Conclusion: The prevalence of BHD in the general population is about 2 cases per million, without difference between genders.

Metastatic follicular thyroid cancer in a patient with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHDS) is an extremely rare genetic condition that predisposes to renal cell carcinoma. This case describes a novel case of a patient with BHDS who also develops follicular thyroid cancer.

The clinical characteristics of East Asian patients with Birt-Hogg-Dubé syndrome

Background

Birt-Hogg-Dube (BHD) syndrome is an autosomal dominant disease that has been characterized by skin lesions, multiple pulmonary cysts, spontaneous pneumothorax, and renal tumors, but the patients in Asian countries may show fewer symptoms. We aimed to explore and summarize the clinical features of BHD patients in East Asia to facilitate early diagnosis and timely interventions.

Methods

We collected and analyzed the clinical data of patients diagnosed with BHD in our hospital by reviewing medical records. We performed a systematic literature search regarding the presenting clinical features in BHD patients from China, Japan, and Korea and then reviewed the publications that were identified.

Results

In our hospital, 10 patients were diagnosed with BHD from April 2015 to September 2019. After reviewing the literature, we recruited 38 articles, including 12, 20, and 6 reports from China, Japan, and Korea, respectively. A total of 166 patients were included in this study, and 100 of them (60.2%) were females. Multiple pulmonary cysts were present in 145 patients (87.3%), and 124 patients (74.7%) had a history of pneumothorax on at least one occasion. Skin biopsy confirmed fibrofolliculomas (FFs) alone in 22 patients (13.3%), trichodiscomas (TDs) alone in 3 patients (1.8%), and both FFs and TDs in 7 patients (4.2%). Renal carcinoma only occurred in 12 (7.2%) patients. The most frequent genetic mutations in East Asian patients were c.1285delC on exon 11 (18.4%), c.1285dupC on exon 11 (18.4%), and c.1347_1353dupCCACCCT on exon 12 (8.2%).

Conclusions

Our findings suggested that pulmonary cysts are the most frequent radiological findings, and pneumothorax is the most common symptom in East Asian patients with BHD, and that skin lesions and kidney involvement are less frequent. To make an early diagnosis and minimize the severity of complications, careful observation, and timely genetic examination of the FLCN gene is essential.

Birt-Hogg-Dubé syndrome

Birt–Hogg–Dubé syndrome (BHD) is a rare inherited autosomal dominant disorder caused by germline mutations in the tumour suppressor gene FLCN, encoding the protein folliculin. Its clinical expression typically includes multiple pulmonary cysts, recurrent spontaneous pneumothoraces, cutaneous fibrofolliculomas and renal tumours of various histological types. BHD has no sex predilection and tends to manifest in the third or fourth decade of life. Multiple bilateral pulmonary cysts are found on chest computed tomography in >80% of patients and more than half experience one or more episodes of pneumothorax. A family history of pneumothorax is an important clue, which suggests the diagnosis of BHD. Unlike other cystic lung diseases such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis, BHD does not lead to progressive loss of lung function and chronic respiratory insufficiency. Renal tumours affect about 30% of patients during their lifetime, and can be multiple and recurrent. The diagnosis of BHD is based on a combination of genetic, clinical and/or skin histopathological criteria. Management mainly consists of early pleurodesis in the case of pneumothorax, periodic renal imaging for tumour detection, and diagnostic work-up in search of BHD in relatives of the index patient.

Birt–Hogg–Dubé syndrome is a rare genetic disorder characterised by multiple lung cysts, recurrent pneumothoraces, skin lesions and kidney tumours. As the presenting symptoms may be respiratory, chest physicians should be able to identify this disease.https://bit.ly/2xsOTuk

Appendiceal diverticulosis in a patient with family history of Birt-Hogg-Dubé syndrome--a case report

Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominant disorder that predisposes patients to cutaneous tumors, pulmonary cysts with recurrent spontaneous pneumothoraces, and a variety of renal neoplasms including hybrid oncocytic and chromophobe renal cell carcinomas. There has been much debate regarding the genetic link with the occurrence of colorectal cancer and other colonic anomalies. Associations between BHD and intestinal adenomatous polyposis and sigmoid diverticulosis have been described in the literature, but there have been no prior reports of appendiceal diverticulosis in patients with BHD. Here, we present a 40-year-old female patient with a known family history of BHD, who was found to have diverticulosis of the appendix and pulmonary blebs on computed tomography upon routine screening for renal and pulmonary abnormalities, suggesting additional focus be given to the gastrointestinal tract (including the appendix) at the time of CT assessment.

Focus on the pulmonary involvement and genetic patterns in Birt-Hogg-Dubè syndrome: Literature review

INTRODUCTION

Brit-Hogg-Dubé syndrome (BHD) is a rare disorder that is estimated to affects about 600 families in the World. The disease-causing mutations is on FLCN gene which codes for folliculin. This protein has a role in different organs as skin, kidney and lung, thanks to the interaction with type I and II cadherins, RhoA activity and the regulation of AMPK, mTORC1 pathways and cell adhesion. The aim of our study is to focus on the manifestation of the syndrome, especially the pulmonary involvement, then on genetical analysis and on the available treatments.

MATERIAL AND METHODS

We collected 15 previous studies where we found medical history information, clinical manifestations, radiological and histological diagnosis and genetical analysis.

RESULTS

The prevalence of pneumothorax in patients with BHD syndrome was about 65%, but the lung involvement with multiple small cysts, localized especially in the lower part, was 85%. The prevalence of renal involvement in BHD patients ranged from 6.5% to 34%, while skin lesions ranged from 11% to 50%. More than 150 FLCN germline has been described, though the mutation in exon 11 is the most frequently detected, especially among Caucasian population.

CONCLUSIONS

BHD syndrome is rare and usually the first manifestations appear in early age. In patients with these clinical and radiological characteristics we suggest taking a careful medical history, though the diagnosis of BHD syndrome should be confirmed with the analysis of FLCN gene.

No evidence for increased prevalence of colorectal carcinoma in 399 Dutch patients with Birt-Hogg-Dubé syndrome

Background

Previously, it has been suggested that colorectal polyps and carcinomas might be associated with Birt-Hogg-Dubé syndrome. We aimed to compare the occurrence of colorectal neoplasms between Dutch patients with Birt-Hogg-Dubé syndrome and their relatives without Birt-Hogg-Dubé syndrome.

Methods

In all, 399 patients with a pathogenic FLCN mutation and 382 relatives without the familial FLCN mutation were included. Anonymous data on colon and rectum pathology was provided by PALGA: the Dutch Pathology Registry.

Results

No significant difference in the percentage of individuals with a history of colorectal carcinoma was found between the two groups (3.6% vs 2.6%, p = 0.54). There was also no significant difference between the age at diagnosis, diameter, differentiation and location of the colorectal carcinomas. Significantly more individuals with Birt-Hogg-Dubé syndrome underwent removal of colorectal polyps (12.2% vs 6.3%, p = 0.005). However, there was no significant difference between the number of polyps per person, the histology, grade of dysplasia and location of the polyps.

Conclusion

Our data do not provide evidence for an increased risk for colorectal carcinoma in Birt-Hogg-Dubé syndrome, arguing against the need for colorectal surveillance. The difference in polyps might be due to a bias caused by a higher number of colonoscopies in patients with Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome-associated renal cell carcinoma: Histopathological features and diagnostic conundrum

Birt‐Hogg‐Dubé (BHD) syndrome is associated with the development of hereditary renal cell carcinoma (RCC) and is caused by a germline mutation in the folliculin gene. Most cases of BHD syndrome‐associated RCC (BHD‐RCC) are less aggressive than sporadic clear cell RCC and multifocal. Therefore, it is critical to distinguish BHD‐RCC from its sporadic counterparts to identify and monitor affected families and to preserve renal function for as long as possible. The World Health Organization/International Society of Urological Pathology consensus classification defined distinct entities for certain hereditary RCC; however, BHD‐RCC was not included in this classification. Although the clinical features and molecular mechanisms of BHD‐RCC have been investigated intensively over the last two decades, pathologists and urologists occasionally face difficulties in the diagnosis of BHD‐RCC that require genetic testing. Affected patients usually have miscellaneous benign disorders that often precede renal carcinogenesis. In the present review, we summarize the current understanding of the histopathological features of BHD‐RCC based on our epidemiological studies of Japanese families and a literature review. Pathological diagnostic clues and differential diagnosis of BHD‐RCC from other hereditary RCC are also briefly discussed.

Genotypic characteristics of Chinese patients with BHD syndrome and functional analysis of FLCN variants

Background

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant disease featured by lung cysts, spontaneous pneumothorax, fibrofolliculomas and renal tumors. The causative gene for BHDS is the folliculin (FLCN) gene and more than 200 mutations have been reported in FLCN, mostly truncating mutations. The aim of this study is to better characterize the clinical features and mutation spectrum of Chinese BHDS patients and to systematically evaluate the effects of non-truncating mutations on mRNA splicing pattern.

Methods

We enrolled 47 patients from 39 unrelated families with symptoms highly suggestive of BHDS after informed consent and detailed clinical data were collected. Exon sequencing followed by multiplex ligation-dependent probe amplification testing were applied for mutation screening. The effects of non-truncating mutations, including 15 missense mutations and 6 in-frame deletions, on mRNA splicing were investigated by minigene assays.

Results

A total of 24 FLCN germline variants were found in 39 patients from 31 distinct families. Out of these patients, 100% (36/36) presented with lung cysts and 58.3% (21/36) had experienced spontaneous pneumothorax. Seventeen mutation carriers had skin lesions (47.2%, 17/36) and 9 (30%, 9/30) had kidney lesions including 8 with renal cysts and 1 with renal hamartoma. Among all detected variants 14 (58.3%, 14/24) were novel, including 11 variants classified to be pathogenic and 3 variants of uncertain significance. None of 21 non-truncating mutations changed the mRNA splicing pattern of minigenes.

Conclusions

We found different clinical features of Chinese BHDS patients compared with Caucasians, with more lung cysts and pneumothorax but fewer skin lesions and malignant renal cancer. Chinese patients with BHDS also have a different mutation spectrum from other races. Non-truncating mutations in FLCN did not disrupt mRNA splicing pattern, in turn supporting the hypothesis that these mutations impair folliculin function by disrupting the stability of the FLCN gene product.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1198-y) contains supplementary material, which is available to authorized users.

Birt-Hogg-Dubé syndrome in Korean: clinicoradiologic features and long term follow-up

BACKGROUND/AIMS

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disorder that is characterized by skin fibrofolliculomas, pulmonary cysts, and renal tumors. The objective of this study was to describe the features of Korean patients with BHD syndrome.

METHODS

Clinical data were retrospectively reviewed in 12 patients (10 confirmed by direct sequencing of the folliculin (FLCN) gene and two confirmed by clinical diagnosis) diagnosed from 2004 to 2016 at Asan Medical Center, Seoul, South Korea. Criteria proposed by the European BHD consortium were used for diagnosis.

RESULTS

The median follow-up was 52 months. The mean age was 41.3 years and 66.7% were female. Eight patients (66.7%) had a history of pneumothorax, which was recurrent in 75%. Skin lesions were detected in 25.0% and renal cancer in 25.0%. Among mutations of the FLCN gene, the duplication of cytosine in the C8 tract of exon 11 (c.1285dupC) was the most common (40%); however, a novel heterozygous sequence variant of c.31T>C (p.C11R) in exon 4 was detected in one patient. All patients had multiple and bilateral pulmonary cysts, distributed in predominantly lower, peripheral and subpleural regions of the lungs. Most patients showed preserved lung function that remained unchanged during follow-up, and two (16.7%) developed cancers (renal cancer in one and breast cancer in one).

CONCLUSION

Our data suggest that Korean patients with BHD syndrome may have a higher risk of pneumothorax, less frequent skin lesions, and a novel FLCN mutation compared to previous reports. Multiple bilateral and basal-predominant cysts were the most common radiologic features.

Renal Manifestation of Birt-Hogg-Dubé Syndrome Depicted by 18F-fludeoxyglucose Positron Emission Tomography/Computed Tomography in a Patient with Hurtle Cell Thyroid Malignancy

Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant genetic disorder characterized by small papular skin lesions (fibrofolliculomas) causing susceptibility to kidney cancer, renal and pulmonary cysts, spontaneous pneumothoraces, and several noncutaneous tumors. We report a case of a 67-year-old woman, with a previous history of right hemithyroidectomy for adenomatous lesion. She presented with a swelling in the right thyroid bed that on subsequent biopsy revealed features of metastatic carcinoma. 18F-fludeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) performed for the detection of primary malignancy showed increased high-grade metabolic activity in the right supraclavicular soft tissue mass extending into the superior mediastinum. Moreover, on low-dose CT, there have been bilateral renal interpolar cortical lesions with mild metabolic activity. Given the fact that the right neck mass was highly unlikely to represent renal metastases in the absence of widespread metastatic disease, surgical excision of the right neck mass was performed. The histology of the mass was in keeping with hurtle cell thyroid carcinoma. In regard to renal lesions, bilateral partial nephrectomy was performed, which was consistent with chromophobe renal cell carcinoma, raising the suspicion of BHD that was confirmed by the subsequent genetic evaluation. It is well established that 18F-FDG PET/CT study is not an optimal modality for evaluation of renal lesions. However, careful assessment of the CT features in conjunction with the associated metabolic activity of the 18F-FDG PET component increases the diagnostic accuracy of PET/CT.

Childhood pneumothorax in Birt-Hogg-Dubé syndrome: A cohort study and review of the literature

Background

Birt‐Hogg‐Dubé syndrome (BHD) is an autosomal dominantly inherited cancer predisposition syndrome associated with an increased risk of spontaneous pneumothorax (SP) and renal cell carcinoma in the adult population. Recent studies suggest that BHD accounts for up to 10% of all SP in adults and BHD in children with SP have been reported.

Methods

To explore to what extent BHD is the cause of childhood pneumothorax, we studied a Danish BHD cohort consisting of 109 cases from 22 families. Clinical data was gathered by review of medical records. A systematic literature search concerning childhood and adolescence pneumothorax in BHD was performed and identified publications reviewed.

Results

In our cohort, three of 109 BHD cases experienced childhood pneumothorax, corresponding to a prevalence of 3%. Reviewing the literature, data regarding more than 800 BHD cases were covered. Only seven previously published cases of childhood pneumothorax in BHD were identified.

Conclusion

Our findings suggest that BHD is likely the cause of a larger subset of childhood pneumothoraces than hitherto recognized. Awareness of BHD as a cause of childhood pneumothorax needs to be raised to provide patients and relatives with the possibility of specialized management of SP and regular renal cancer surveillance.

Birt-Hogg-Dubé Syndrome: A Review of Dermatological Manifestations and Other Symptoms

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant genodermatosis with malignant potential characterized by cutaneous and extracutaneous stigmata. Aberrations in the folliculin (FLCN) gene, which is located on chromosome 17, have been discovered in individuals with this condition. Over 150 unique mutations have been identified in BHD. The skin lesions associated with this condition include fibrofolliculomas, trichodiscomas, perifollicular fibromas, and acrochordons. Extracutaneous features of the syndrome typically include the lung (spontaneous pneumothorax and cysts) and the kidney (neoplasms). The only malignancies associated with BHD are renal cancers; however, other tumors have been observed in individuals with BHD. In this article, the skin lesions associated with this condition are reviewed, lung and renal manifestations associated with this syndrome are presented, and malignancies occurring in these patients are summarized.

Birt-Hogg-Dubé syndrome in two Chinese families with mutations in the FLCN gene

Background

Birt-Hogg-Dubé syndrome is an autosomal dominant hereditary condition caused by mutations in the folliculin-encoding gene FLCN (NM_144997). It is associated with skin lesions such as fibrofolliculoma, acrochordon and trichodiscoma; pulmonary lesions including spontaneous pneumothorax and pulmonary cysts and renal cancer.

Methods

Genomic DNA was extracted from peripheral venous blood samples of the propositi and their family members. Genetic analysis was performed by whole exome sequencing and Sanger sequencing aiming at corresponding exons in FLCN gene to explore the genetic mutations of these two families.

Results

In this study, we performed genetic analysis by whole exome sequencing and Sanger sequencing aiming at corresponding exons in FLCN gene to explore the genetic mutations in two Chinese families. Patients from family 1 mostly suffered from pneumothorax and pulmonary cysts, several of whom also mentioned skin lesions or kidney lesions. While in family 2, only thoracic lesions were found in the patients, without any other clinical manifestations. Two FLCN mutations have been identified: One is an insertion mutation (c.1579_1580insA/p.R527Xfs on exon 14) previously reported in three Asian families (one mainland family and two Taiwanese families); while the other is a firstly reviewed mutation in Asian population (c.649C > T / p.Gln217X on exon 7) that ever been detected in a French family.

Conclusions

Overall, The detection of these two mutations expands the spectrum of FLCN mutations and will provide insight into genetic diagnosis and counseling of Birt-Hogg-Dubé syndrome.

FLCN: The causative gene for Birt-Hogg-Dubé syndrome

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 PGC1α 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.

The roles of intrinsic disorder-based liquid-liquid phase transitions in the "Dr. Jekyll-Mr. Hyde" behavior of proteins involved in amyotrophic lateral sclerosis and frontotemporal lobar degeneration

Pathological developments leading to amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are associated with misbehavior of several key proteins, such as SOD1 (superoxide dismutase 1), TARDBP/TDP-43, FUS, C9orf72, and dipeptide repeat proteins generated as a result of the translation of the intronic hexanucleotide expansions in the C9orf72 gene, PFN1 (profilin 1), GLE1 (GLE1, RNA export mediator), PURA (purine rich element binding protein A), FLCN (folliculin), RBM45 (RNA binding motif protein 45), SS18L1/CREST, HNRNPA1 (heterogeneous nuclear ribonucleoprotein A1), HNRNPA2B1 (heterogeneous nuclear ribonucleoprotein A2/B1), ATXN2 (ataxin 2), MAPT (microtubule associated protein tau), and TIA1 (TIA1 cytotoxic granule associated RNA binding protein). Although these proteins are structurally and functionally different and have rather different pathological functions, they all possess some levels of intrinsic disorder and are either directly engaged in or are at least related to the physiological liquid-liquid phase transitions (LLPTs) leading to the formation of various proteinaceous membrane-less organelles (PMLOs), both normal and pathological. This review describes the normal and pathological functions of these ALS- and FTLD-related proteins, describes their major structural properties, glances at their intrinsic disorder status, and analyzes the involvement of these proteins in the formation of normal and pathological PMLOs, with the ultimate goal of better understanding the roles of LLPTs and intrinsic disorder in the "Dr. Jekyll-Mr. Hyde" behavior of those proteins.

Emerging entities in renal cell neoplasia: thyroid-like follicular renal cell carcinoma and multifocal oncocytoma-like tumours associated with oncocytosis

The list of accepted entities of renal cell neoplasia has burgeoned since the turn of the century through recognition of rare tumour types and the discovery of genetic mutations driving renal neoplasia syndromes. This growth has not finished and in this report we present examples of each of these types which were not included in the 2016 World Health Organization classification of renal neoplasia, but are candidates for inclusion in the next edition of the classification. Thyroid-like follicular renal cell carcinoma is a rare tumour type with a distinctive microscopic appearance resembling follicles of the thyroid gland. Thirty-nine cases have been described and the findings have been reasonably consistent. Oncocytoma-like tumours associated with oncocytosis arise as a result of somatic mutations in the mitochondrial genome. The differential diagnosis is mainly with the renal lesions of the Birt-Hogg-Dubé syndrome, which is the result of germline mutations in the folliculin gene. Patients with oncocytoma-like tumours associated with oncocytosis are at great risk of developing renal failure as the proliferating lesions replace the renal parenchyma. Oncocytoma-like tumours have never been found to metastasise.

Skin lesions of Birt-Hogg-Dubé syndrome: Clinical and histopathological findings in 31 Japanese patients who presented with pneumothorax and/or multiple lung cysts

BACKGROUND

Birt-Hogg-Dubé syndrome (BHDS) (OMIM #135150) is an autosomal dominant disease, characterized by fibrofolliculomas (FFs) of the skin, pulmonary cysts with/without pneumothorax, and renal tumors. The prevalence of skin manifestations reported for Japanese BHDS patients is lower (<30%) compared with that of Western countries (75∼90%), which appear to be underestimated.

OBJECTIVE

To precisely examine the prevalence of skin lesions with dermoscopy and histopathology with reference to genetic analyses.

METHODS

We studied 31 patients (47.0±13.2years old, range 15-71) consisting of 26 unrelated families consecutively from May 2013 to June 2015 specifically for skin-colored papules on their faces and cervicothoracic regions. Patients initially suspected of BHDS from multiple pulmonary cysts that resulted in pneumothorax (30/31; 96.8%) received dermoscopic examinations and skin biopsies if applicable. The diagnosis of BHDS was established by folliculin (FLCN) genetic testing, and the results were compared to the histopathological findings of FFs or trichodiscomas (TDs).

RESULTS

FLCN germline mutation was demonstrated in 25/26 (96.2%) unrelated families tested and 28/29 patients (96.6%) tested. Skin lesions were recognized in 26/31 patients (83.9%); skin biopsies were performed in 23 patients of whom FFs and/or TDs were histologically demonstrated in 17 (73.9%). Although our study population included patients whose skin manifestations were evaluated prior to or after FLCN genetic testing, skin lesions were clearly prevalent and recognizable irrespective of whether genetic testing was or wasn't done. When examined with dermoscopy, distinct FFs appeared as well-demarcated areas of pallor with central follicular openings in 13 of 15 FF-bearing patients (86.7%); however, those manifestations were not recognized for TD.

CONCLUSIONS

Skin lesions appear to be more prevalent than previously reported (<30% vs.73.9%) in Japanese BHDS patients. Dermoscopy is a useful diagnostic aid for finding FFs.

Clinical and genetic study of a large Chinese family presented with familial spontaneous pneumothorax

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.

Birt-Hogg-Dubé syndrome: a literature review and case study of a Chinese woman presenting a novel FLCN mutation

BACKGROUND

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.

CASE PRESENTATION

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.

CONCLUSION

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.

Birt-Hogg-Dubé syndrome: a case report and a review of the literature

Background: Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal dominant inherited syndrome caused by mutations in the folliculin coding gene (FLCN). The clinical manifestations of the syndrome involve the skin, lungs, and kidneys. Because of the rarity of the syndrome, guidelines for diagnosis and management of the patients with BHDS are lacking.

Objective: To present a case story and a review of the literature on BHDS in order to give an update on genetics, clinical manifestations, diagnosis, treatment, prognosis and follow-up strategies.

Design: Literature review and case story.

Results: A PubMed and Embase search identified 330 papers. BHDS is characterized by small benign tumors in the skin, spontaneous pneumothoraces caused by cysts in the lungs and a seven-fold increased risk of renal cancer. A case story of a young female patient presenting with pneumothorax and a family history of recurrent pneumothoraces in many relatives illustrates how the history and the diagnostic work up resulted in a diagnosis of BHDS.

Conclusion: BHDS is a rare inherited disorder. In patients with spontaneous pneumothorax or cystic lung disease without any obvious explanation, BHDS should be considered. Concomitant skin manifestations, a family history of familiar pneumothorax, renal cancers and skin manifestations supports the suspicion of BHDS. Early diagnosis is important in order to subject patients to systematic screening for renal cancers. A radiological surveillance strategy for renal cancer is proposed.

Novel germline mutations in FLCN gene identified in two Chinese patients with Birt-Hogg-Dubé syndrome

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).

Renal angiomyolipoma in Birt-Hogg-Dube syndrome: A case study supporting overlap with tuberous sclerosis complex

Birt-Hogg-Dube syndrome (BHD) is an autosomal dominant disease characterised by benign cutaneous lesions, pulmonary cysts, and an increased risk of renal tumors. This rare condition is due to a mutation in the folliculin (FLCN) gene on chromosome 17q11.2, which has a role in the mechanistic/mammalian target of rapamycin (mTOR) signaling pathway of tumorigenesis. This case illustrates a patient with BHD and a renal angiomyolipoma, a neoplastic lesion not usually associated with BHD but common in Tuberous Sclerosis Complex (TSC). There is both clinical and molecular overlap between BHD and TSC, which may arise from similarities in function of the TSC and FLCN proteins in the mTOR pathway; this case further demonstrates this potential correlation. © 2016 Wiley Periodicals, Inc.

Case Report of Birt-Hogg-Dubé Syndrome: Germline Mutations of FLCN Detected in Patients With Renal Cancer and Thyroid Cancer

Birt-Hogg-Dubé (BHD) is a rare autosomal dominant inherited syndrome that is characterized by the presence of fibrofolliculomas and/or trichodiscomas, pulmonary cysts, spontaneous pneumothorax, and renal tumors. Here, the 2 patients we reported with renal cell carcinomas and dermatological features were suspected to be suffering from BHD syndrome. Blood samples of these patients were sent for whole exon sequencing performed by Sanger sequencing. Eight mutations, including 5 mutations, which were mapped in noncoding region, 1 synonymous mutation, and 2 missense mutations, were detected in the FLCN gene in both patients. The 2 missense mutations, predicted to be disease-causing mutation or affecting protein function by MutationTaster and SIFT, confirmed the diagnosis. In addition, the 2 patients were also affected with papillary thyroid cancer. Total thyroidectomy and prophylactic bilateral central lymph node dissection were performed for them and the BHD-2 also received lateral lymph node dissection. Pathology reports showed that the patients had lymph node metastasis in spite of small size of thyroid lesions.The 2 missense mutations, not reported previously, expand the mutation spectrum of FLCN gene associated with BHD syndrome. For the thyroid cancer patients with BHD syndrome, total thyroidectomy and prophylactic bilateral central lymph node dissection may be suitable and the neck ultrasound may benefit BHD patients and their family members.

Birt-Hogg-Dubé syndrome: Clinical and molecular aspects of recently identified kidney cancer syndrome

Birt-Hogg-Dubé syndrome is an autosomal dominantly inherited disease that predisposes patients to develop fibrofolliculoma, lung cysts and bilateral multifocal renal tumors, histologically hybrid oncocytic/chromophobe tumors, chromophobe renal cell carcinoma, oncocytoma, papillary renal cell carcinoma and clear cell renal cell carcinoma. The predominant forms of Birt-Hogg-Dubé syndrome-associated renal tumors, hybrid oncocytic/chromophobe tumors and chromophobe renal cell carcinoma are typically less aggressive, and a therapeutic principle for these tumors is a surgical removal with nephron-sparing. The timing of surgery is the most critical element for postoperative renal function, which is one of the important prognostic factors for Birt-Hogg-Dubé syndrome patients. The folliculin gene (FLCN) that is responsible for Birt-Hogg-Dubé syndrome was isolated as a novel tumor suppressor for kidney cancer. Recent studies using murine models for FLCN, a protein encoded by the FLCN gene, and its two binding partners, folliculin-interacting protein 1 (FNIP1) and folliculin-interacting protein 2 (FNIP2), have uncovered important roles for FLCN, FNIP1 and FNIP2 in cell metabolism, which include AMP-activated protein kinase-mediated energy sensing, Ppargc1a-driven mitochondrial oxidative phosphorylation and mTORC1-dependent cell proliferation. Birt-Hogg-Dubé syndrome is a hereditary hamartoma syndrome, which is triggered by metabolic alterations under a functional loss of FLCN/FNIP1/FNIP2 complex, a critical regulator of kidney cell proliferation rate; a mechanistic insight into the FLCN/FNIP1/FNIP2 pathway could provide us a basis for developing new therapeutics for kidney cancer.

Molecular genetics and clinical features of Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé (BHD) syndrome is an inherited renal cancer syndrome in which affected individuals are at risk of developing benign cutaneous fibrofolliculomas, bilateral pulmonary cysts and spontaneous pneumothoraces, and kidney tumours. Bilateral multifocal renal tumours that develop in BHD syndrome are most frequently hybrid oncocytic tumours and chromophobe renal carcinoma, but can present with other histologies. Germline mutations in the FLCN gene on chromosome 17 are responsible for BHD syndrome--BHD-associated renal tumours display inactivation of the wild-type FLCN allele by somatic mutation or chromosomal loss, confirming that FLCN is a tumour suppressor gene that fits the classic two-hit model. FLCN interacts with two novel proteins, FNIP1 and FNIP2, and with AMPK, a negative regulator of mTOR. Studies with FLCN-deficient cell and animal models support a role for FLCN in modulating the AKT-mTOR pathway. Emerging evidence links FLCN with a number of other molecular pathways and cellular processes important for cell homeostasis that are frequently deregulated in cancer, including regulation of TFE3 and/or TFEB transcriptional activity, amino-acid-dependent mTOR activation through Rag GTPases, TGFβ signalling, PGC1α-driven mitochondrial biogenesis, and autophagy. Currently, surgical intervention is the only therapy available for BHD-associated renal tumours, but improved understanding of the FLCN pathway will hopefully lead to the development of effective forms of targeted systemic therapy for this disease.

FLCN intragenic deletions in Chinese familial primary spontaneous pneumothorax

Primary spontaneous pneumothorax (PSP) is a significant clinical problem, affecting tens of thousands patients annually. Germline mutations in the FLCN gene have been implicated in etiology of familial PSP (FPSP). Most of the currently identified FLCN mutations are small indels or point mutations that detected by Sanger sequencing. The aim of this study was to determine large FLCN deletions in PSP families that having no FLCN sequence-mutations. Multiplex ligation-dependent probe amplification (MLPA) assays and breakpoint analyses were used to detect and characterize the deletions. Three heterozygous FLCN intragenic deletions were identified in nine unrelated Chinese families including the exons 1-3 deletion in two families, the exons 9-14 deletion in five families and the exon 14 deletion in two families. All deletion breakpoints are located in Alu repeats. A 5.5 Mb disease haplotype shared in the five families with exons 9-14 deletion may date the appearance of this deletion back to approximately 16 generations ago. Evidences for founder effects of the other two deletions were also observed. This report documents the first identification of founder mutations in FLCN, as well as expands mutation spectrum of the gene. Our findings strengthen the view that MLPA analysis for intragenic deletions/duplications, as an important genetic testing complementary to DNA sequencing, should be used for clinical molecular diagnosis in FPSP.

Cystic lung disease in birt-hogg-dubé syndrome: a case series of three patients

Birt-Hogg-Dubé syndrome is characterized by clinical manifestations such as hamartomas of the skin, renal tumors and lung cysts with spontaneous pneumothoraces. Patients with Birt-Hogg-Dubé syndrome may present with only multiple lung cysts. We report the chest computerized tomography (CT) features of three patients with Birt-Hogg-Dubé syndrome. Each patient had multiple lung cysts of various sizes according to chest CT evaluation, most of which were located in lower lobes and related to pleura. The identification of unique characteristics in the chest CT of patients with Birt-Hogg-Dubé syndrome may provide an efficient mechanism for diagnosis.

A rare soft tissue tumor masquerading as a parathyroid adenoma in a patient with birt-hogg-dubé syndrome and multiple cervical endocrinopathies

Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant disorder that presents with renal tumors, pulmonary cysts with spontaneous pneumothoraces, and skin hamartomas. We present a case of a 67-year-old female with multiple endocrinopathies and a history of BHD syndrome. In 2011, a thyroidectomy with a four-gland parathyroidectomy was performed for toxic multinodular goiter (TMNG) and parathyroid hyperplasia. On frozen section, a tumor was identified next to a hypercellular parathyroid. After being worked up, this tumor was determined to be an adult rhabdomyoma. This represents the first time that both TMNG and parathyroid hyperplasia have been present in a BHD patient. Additionally, this is the first adult rhabdomyoma reported in a patient with BHD syndrome. Adult rhabdomyomas have no reported associations; however, potential colocation of the mutation in BHD syndrome and translocation in adult rhabdomyomas on chromosome 17p suggests a possible connection. Further work is needed to better understand this connection.