Lung cysts, spontaneous pneumothorax, and genetic associations in 89 families with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome - a rare genetic disorder complicated by pneumothorax: A case report

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare genetic disorder associated with mutations in the BHD gene, which can manifest symptoms at any age, including dermatological and pulmonary complications, as well as renal tumors. This study presents a case of a BHD patient who experienced spontaneous pneumothorax, aiming to enhance the understanding of this syndrome.

CASE SUMMARY

A 42-year-old female patient presented with left-sided chest pain and tightness lasting three days. Chest computed tomography scans revealed left-sided pneumothorax and multiple pulmonary bullae. Physical examination indicated decreased vocal fremitus and tympanic percussion on the left side. A thorough family history revealed a pattern of pulmonary disorders, including emphysema, spontaneous pneumothorax, and lung cancer among relatives. Genetic testing identified a heterozygous frameshift mutation in the FLCN gene at the 17p11.2 locus. Based on the clinical presentation, imaging findings, family history, and genetic results, the patient was suspected to have BHD syndrome.

CONCLUSION

We present a case of a heterozygous mutation in the FLCN gene in a patient with BHD syndrome, aiming to review the associated clinical characteristics and genetic mechanisms of this condition. This case serves as a reference point to offer insights into the diagnosis of multiple pulmonary cysts and spontaneous pneumothorax of unknown etiology in clinical practice.

The prevalence of spontaneous pneumothorax in patients with BHD syndrome: a systematic review and meta-analysis

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is associated with an increased risk of pneumothorax. This study aimed to determine the prevalence of spontaneous pneumothorax among individuals diagnosed with BHD syndrome.

METHOD

A comprehensive literature search was conducted across PubMed, EMBASE, Cochrane Controlled Register of Trials (CENTRAL), and Web of Science databases up to March 10, 2024. Studies reporting on the prevalence of spontaneous pneumothorax in BHD syndrome patients were included. Eligibility assessment, data extraction, and quality assessment were performed independently by two reviewers. Random-effects or fixed-effect models were conducted to calculate pooled incidence rates, and subgroup analyses were performed to explore sources of heterogeneity. The publication bias was assessed by funnel plot and Egger's test.

RESULTS

Eighteen studies, conducted between 2009 and 2023, were included in the systematic review. The meta-analysis revealed a pooled incidence rate of spontaneous pneumothorax in BHD syndrome patients at 0.61 (95% CI 0.46; 0.76). Subgroup analyses based on region, study design, and diagnostic methods further elucidated variations in incidence rates among different patient groups. Specifically, the Asian subgroup demonstrated a higher pooled incidence rate of 0.71 (95% CI 0.60; 0.81), while the Caucasian subgroup showed a lower pooled incidence rate of 0.43 (95% CI 0.26; 0.60). The subgroup analysis by study design revealed a pooled incidence rate of 0.60 (95% CI 0.45; 0.76) for retrospective studies and 0.70 (95% CI 0.42; 0.98) for the sole prospective study. Additionally, the subgroup analysis by diagnostic methods showed pooled incidence rates of 0.64 (95% CI 0.48; 0.81) for studies using FLCN mutation testing and 0.51 (95% CI 0.33; 0.70) for those using clinical criteria and imaging findings. Potential publication bias was identified by Egger's test (P < 0.05).

CONCLUSION

The study indicated a pooled prevalence rate of 61% for pneumothorax in BHD syndrome patients, with subgroup analyses revealing higher rates among Asian individuals and in prospective studies. Further researches, particularly large-sample prospective studies, are needed to address publication bias and improve the reliability of prevalence estimates.

PROSPERO

CRD42024567520.

Features of Lung Cyst in Birt-Hogg-Dubé Syndrome from Patients with Multiple Lung Cysts

BACKGROUND

High-resolution chest computed tomography (CT) is a crucial assessment tool for diagnosing Birt-Hogg-Dubé (BHD) syndrome. This study aimed to analyze differences of lung cysts between BHD and other cystic lung diseases.

METHODS

From January 2020 to December 2022, patients with multiple lung cysts who underwent chest CT at Gangnam Severance Hospital were included.

RESULTS

Over a 3-year period (from January 2020 to December 2022), out of 52,823 patients who underwent a chest CT scan, 301 (0.6%) patients with multiple lung cysts were enrolled in this study. Of enrolled patients, 24 (8.0%) were diagnosed with BHD. In patients with BHD, 95.8% exhibited bilateral cysts, and 83.3% showed basal predominance. The cysts' maximal diameter averaged 32.1 mm (interquartile range, 26.5 to 43.5). Additionally, 95.8% of patients with BHD had diverse cyst sizes and morphologies. Multivariate logistic regression analysis revealed that bilateral cysts (odds ratio [OR], 12.393; 95% confidence interval [CI], 1.613 to 274.682; p=0.038), basal predominance (OR, 8.511; 95% CI, 2.252 to 39.392; p=0.002), maximum diameter (OR, 1.053; 95% CI, 1.009 to 1.108; p=0.032), and diversity of morphology (OR, 19.513; 95% CI, 2.833 to 398.119; p=0.010) were significant factors associated with BHD diagnosis. A multivariate prediction model for BHD diagnosis demonstrated a sensitivity of 95.83%, a specificity of 81.22%, and an area under the receiver operating characteristic curve of 0.951 (95% CI, 0.914 to 0.987).

CONCLUSION

Distinguishing features of lung cysts from other cystic lung diseases include bilateral cysts, basal dominance, large size, and irregular shape.

Familial analysis: pulmonary Birt-Hogg-Dubé syndrome in two siblings

Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal dominant genetic disorder. This case report aims to increase awareness of pulmonary cystic lesions and BHDS in China by providing insights into the clinical features of this syndrome. We present two cases of BHDS from the same family. We describe their clinical presentations, imaging findings, genetic mutations and the disease within their family tree. Two confirmed BHDS patients, initially presented with recurrent pneumothorax. No concurrent skin cystic changes but multiple lung cysts and FLCN gene mutation were found. Additionally, they have a family history of pneumothorax. Colorectal lesions are also noticed in their family. Remarkably, the younger sister also carried a mutation in the MSH6 gene. For patients with lung cysts or pneumothorax on chest CT, it is advisable to trace the family history and remain vigilant for colorectal lesions.

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 .

Rare genetic interstitial lung diseases: a pictorial essay

The main monogenic causes of pulmonary fibrosis in adults are mutations in telomere-related genes. These mutations may be associated with extrapulmonary signs (hepatic, haematological and dermatological) and typically present radiologically as usual interstitial pneumonia or unclassifiable fibrosis. In children, the monogenic causes of pulmonary fibrosis are dominated by mutations in surfactant-related genes. These mutations are not associated with extrapulmonary signs and often manifest radiologically as unclassifiable fibrosis with cysts that can lead to chest wall deformities in adults. This review discusses these mutations, along with most of the monogenic causes of interstitial lung disease, including interferon-related genes, mutations in genes causing cystic lung disease, Hermansky-Pudlak syndrome, pulmonary alveolar proteinosis, lysinuric protein intolerance and lysosomal storage disorders, and their pulmonary and extrapulmonary manifestations.

Computer-aided diagnosis of cystic lung diseases using CT scans and deep learning

BACKGROUND

Auxiliary diagnosis of different types of cystic lung diseases (CLDs) is important in the clinic and is instrumental in facilitating early and specific treatments. Current clinical methods heavily depend on accumulated experience, restricting their applicability in regions with less developed medical resources. Thus, how to realize the computer-aided diagnosis of CLDs is of great clinical value.

PURPOSE

This work proposed a deep learning-based method for automatically segmenting the lung parenchyma in computed tomography (CT) slice images and accurately diagnosing the CLDs using CT scans.

METHODS

A two-stage deep learning method was proposed for the automatic classification of normal cases and five different CLDs using CT scans. Lung parenchyma segmentation is the foundation of CT image analysis and auxiliary diagnosis. To meet the requirements of different sizes of the lung parenchyma, an adaptive region-growing and improved U-Net model was employed for mask acquisition and automatic segmentation. The former was achieved by a self-designed adaptive seed point selection method based on similarity measurement, and the latter introduced multiscale input and multichannel output into the original U-Net model and effectively achieved the lightweight design by adjusting the structure and parameters. After that, the middle 30 consecutive CT slice images of each sample were segmented to obtain lung parenchyma, which was employed for training and testing the proposed multichannel parallel input recursive MLP-Mixer network (MPIRMNet) model, achieving the computer-aided diagnosis of CLDs.

RESULTS

A total of 4718 and 16 290 CT slice images collected from 543 patients were employed to validate the proposed segmentation and classification methods, respectively. Experimental results showed that the improved U-Net model can accurately segment the lung parenchyma in CT slice images, with the Dice, precision, volumetric overlap error, and relative volume difference of 0.96 ± 0.01, 0.93 ± 0.04, 0.05 ± 0.02, and 0.05 ± 0.03, respectively. Meanwhile, the proposed MPIRMNet model achieved appreciable classification effect for normal cases and different CLDs, with the accuracy, sensitivity, specificity, and F1 score of 0.8823 ± 0.0324, 0.8897 ± 0.0325, 0.9746 ± 0.0078, and 0.8831 ± 0.0334, respectively. Compared with classical machine learning and convolutional neural networks-based methods for this task, the proposed classification method had a preferable performance, with a significant improvement of accuracy of 10.74%.

CONCLUSIONS

The work introduced a two-stage deep learning method, which can achieve the segmentation of lung parenchyma and the classification of CLDs. Compared to previous diagnostic tasks targeting single CLD, this work can achieve various CLDs' diagnosis in the early stage, thereby achieving targeted treatment and increasing the potential and value of clinical applications.

Urticarial vasculitis and systemic symptoms as initial presentation of Birt-Hogg-Dubé syndrome: A case report

Birt-Hogg-Dubé syndrome, an extremely rare genetic disorder, is characterized by the development of fibrofolliculomas, lung cysts and subsequent recurrent pneumothorax, and kidney neoplasia. This report highlights the case of a 56-year-old female with a history of right vestibular schwannoma status post stereotactic radiotherapy and vulva bartholin's gland carcinoma who was initially evaluated by primary care for a 6-month history of intermittent, red, raised, widespread rash accompanied by fever, chills, and body aches. A punch biopsy of the rash was performed, which was notable for an urticarial tissue reaction with focal changes of leukocytoclasia and negative direct immunofluorescence. Laboratory tests, which included an autoimmune genetic and periodic fever panel, were unremarkable. Whole genome sequencing returned positive for a pathogenic variant in folliculin gene, consistent with a diagnosis of Birt-Hogg-Dubé syndrome.

Familial pulmonary cysts: A clue to diagnose Birt-Hogg-Dubé syndrome: A case report and literature review

Birt-Hogg-Dubé syndrome (BHD) is an inherited autosomal dominant condition caused by germline mutations in the FLCN gene, mapped to chromosome 17p11.2. Typical manifestations include pulmonary cysts, spontaneous pneumothorax, fibrofolliculomas, and kidney neoplasms. This report details the case of a 56-year-old female non-smoker diagnosed with multiple pulmonary cysts, presenting with a history of recurrent spontaneous pneumothorax. A computed tomography (CT) scan of her daughter revealed similar pulmonary cysts, raising suspicion of BHD. Further abdominal enhanced CT revealed a left renal tumour and cutaneous fibrofolliculomas on her daughter's neck. Consequently, whole-exome sequencing confirmed an FLCN germline mutation in the patient and three relatives, establishing a diagnosis of BHD. This case highlights the importance of familial pulmonary cysts as a clue for diagnosing BHD, providing crucial insights into comparable clinical presentations.

A case report of Birt-Hogg-Dubé syndrome associated with severe airway obstruction in a 62-year-old female smoker

Birt-Hogg-Dubé syndrome (BHD) typically does not manifest airway obstruction despite the presence of multiple lung cysts. However, the long-term effects of cigarette smoking on lung function among individuals with BHD are unknown. We report a case of a smoking individual diagnosed with BHD syndrome complicated by spontaneous pneumothorax and severe airway obstruction. The patient presented with chronic dyspnea and productive cough. Further work-up revealed severe obstructive airflow limitation, and multiple lung cysts in both lungs, accompanied centrilobular emphysematous changes. Genetic testing confirmed a heterozygous deletion of exons 6-8 in the folliculin gene, confirming the diagnosis of BHD.

Hereditary Renal Cancer Syndromes

Familial kidney tumors represent a rare variety of hereditary cancer syndromes, although systematic gene sequencing studies revealed that as many as 5% of renal cell carcinomas (RCCs) are associated with germline pathogenic variants (PVs). Most instances of RCC predisposition are attributed to the loss-of-function mutations in tumor suppressor genes, which drive the malignant progression via somatic inactivation of the remaining allele. These syndromes almost always have extrarenal manifestations, for example, von Hippel-Lindau (VHL) disease, fumarate hydratase tumor predisposition syndrome (FHTPS), Birt-Hogg-Dubé (BHD) syndrome, tuberous sclerosis (TS), etc. In contrast to the above conditions, hereditary papillary renal cell carcinoma syndrome (HPRCC) is caused by activating mutations in the MET oncogene and affects only the kidneys. Recent years have been characterized by remarkable progress in the development of targeted therapies for hereditary RCCs. The HIF2aplha inhibitor belzutifan demonstrated high clinical efficacy towards VHL-associated RCCs. mTOR downregulation provides significant benefits to patients with tuberous sclerosis. MET inhibitors hold promise for the treatment of HPRCC. Systematic gene sequencing studies have the potential to identify novel RCC-predisposing genes, especially when applied to yet unstudied populations.

[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.

Pulmonary interstitial glycogenosis in Birt-Hogg-Dubé syndrome-associated lung cysts: A new insight into the pathogenesis?

Multiple lung cysts are one of the major features of Birt-Hogg-Dubé syndrome (BHD), but little is known about their nature and pathogenesis. We report a case of a woman diagnosed with BHD lung cysts who exhibited pulmonary interstitial glycogenosis (PIG), a mesenchymal abnormality hitherto undescribed in this disease, in specimens resected at 14 and 29 years of age. Histopathologically, oval to spindle clear cells were seen in the subepithelial interstitial tissue of septal structures and the walls of the cysts. They had abundant periodic acid-Schiff-positive cytoplasmic glycogen. Immunohistochemically, these cells were positive for a few markers of mesenchymal stem cell-like lineage, including vimentin, CD44, and CD10, and negative for markers of epithelial or specific mesenchymal differentiation; these results were consistent with the reported immunophenotype of PIG cells. These PIG cells were more abundant in her specimen at age 14 years than in the second specimen from adulthood. The present case suggests that BHD lung cysts belong to a group of pulmonary developmental disorders characterized by combined PIG and alveolar simplification/cystic change. Disorders with PIG may persist until adulthood and may be of clinical and pathological significance.

Clinical phenotype and genetic function analysis of a rare family with hereditary leiomyomatosis and renal cell carcinoma complicated with Birt-Hogg-Dubé syndrome

To date, over 200 families with hereditary leiomyomatosis and renal cell carcinoma (HLRCC) and over 600 families with Birt-Hogg-Dubé (BHD) syndrome have been reported, with low incidence. Here, we describe a patient with suspected rare HLRCC complicated by BHD syndrome. The proband (II1) had characteristic cutaneous leiomyoma-like protrusions on the neck and back, a left renal mass and multiple right renal, liver and bilateral lung cysts. Three family members (I1, II2, II3) had a history of renal cancer and several of the aforementioned clinical features. Two family members (II1, II3) diagnosed with fumarate hydratase (FH)-deficient papillary RCC via pathological biopsy carried two heterozygous variants: FH (NM_000143.3) missense mutation c.1189G>A (p.Gly397Arg) and FLCN (NM_144997.5) frameshift mutation c.1579_1580insA (p.Arg527Glnfs*75). No family member carrying a single variant had renal tumours. In HEK293T cells transfected with mutant vectors, mRNA and protein expression after FLCN p.Arg527Glnfs*75 and FH p.Gly397Arg mutations were significantly lower than those in wild-type (WT) cells. Cell immunofluorescence showed altered protein localisation and reduced protein expression after FLCN p.Arg527Glnfs*75 mutation. The FH WT was uniformly distributed in the cytoplasm, whereas FH protein expression was reduced after the p.Gly397Arg mutation and scattered sporadically with altered cell localisation. Patients with two variants may have a significantly increased penetrance of RCC.

Coexistent Sjogren's syndrome and Birt-Hogg-Dube´ syndrome: a case report

We report a rare case of Sjogren's syndrome complicated with Birt-Hogg-Dubé syndrome (BHDS) not previously mentioned in the literature. Further, there is insufficient evidence linking the two diseases. Here, we review existing diagnostic algorithms for diagnosing diffuse cystic lung disease and provide new insights. The patient initially complained of thirst and dry eyes for ten years, and gradually developed shortness of breath. After admission, physical examination showed five missing teeth, decreased respiratory sounds in both lower lungs, and Velcro rales. Computed tomography showed multiple thin-walled cystic lesions in both lungs. Initial xerophthalmia and labial gland biopsy seemed to reveal a pulmonary cystic change associated with Sjogren's syndrome. Before discharge, a rash suspected to indicate a fibrofollicular tumor in the neck was observed, and then FLCN variant has been found. The challenges how to clarify the diagnosis of DCLD causes are discussed.

Long-term clinical outcomes after initial secondary pneumothorax surgery

Background

Given the heterogeneity of underlying lung disease and the higher morbidity and mortality associated with surgery for secondary pneumothorax (SP), treatment standardization and evidence-based early surgical management are challenging pursuits. Our aim was to document the clinical course of SP after initial surgical intervention and analyse related recurrence risk.

Methods

We conducted a retrospective review of 160 patients, each with SP, using clinical records housed in an institutional database. Clinical, imaging, and operative data were retrieved, and Cox proportional hazards (PH) analysis was undertaken to identify risk factors for recurrence.

Results

During a mean follow-up of 58.7 months, the overall recurrence rate in this cohort was 18.75% (ipsilateral, 14; contralateral, 16). A total of 24 patients had ≥3 ipsilateral episodes <6 months prior to surgery, marked by initial index episodes. In multivariate Cox PH analysis, the strongest risk factor for recurrence was underlying lung pathology other than chronic obstructive pulmonary disease [COPD: hazard ratio (HR) =5.3; P<0.001].

Conclusions

In this setting, underlying lung disease of a non-COPD nature is a proven risk factor for postsurgical recurrence. There is also a tendency in some patients for multiple episodes of pneumothorax within short periods of time, especially in the absence of COPD. Underlying disease processes may thus merit consideration in treatment planning.

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.

Birt-Hogg-Dubé Syndrome: A Rare Genodermatosis Presenting as Skin Papillomas

The authors present a rare case of Birt-Hogg-Dubé (BHD) syndrome that presented primarily as an aesthetic case. Previous providers failed to accurately diagnose BHD, despite the patient's history of pneumothoraces. This female patient complained of numerous recurrent, small skin-colored growths on the face and neck and patchy hypopigmentation from the multiple treatments she had to undergo for her "bumpy skin." She also suffered 4 spontaneous pneumothoraces. Following histopathologic and genetic testing, the patient was diagnosed with BHD. Computed tomography and ultrasound scans revealed multiple cysts in both lungs and an angiomyolipoma in both kidneys. This patient had undergone a variety of treatments to aesthetically remove and heal her skin bumps from several healthcare providers, all of whom had misdiagnosed her condition.

Level of Evidence 5

Pericardial Cyst in Birt-Hogg-Dubé Syndrome: An Unexpected Discovery

Birt-Hogg-Dubé syndrome (BHD) is a genetic disorder typically characterized by pulmonary cysts, cutaneous fibrofolliculomas, and renal tumors. We report a case of an 87-year-old male patient with a known diagnosis of BHD and a large pericardial cyst who presented to the emergency room with chest pain. BHD is classically associated with pulmonary cysts and not pericardial cysts. In this report, we highlight the potential of pericardial cysts to independently cause retrosternal pain resembling angina, while also mentioning that BHD too can cause chest pain through the rupture of a pulmonary cyst leading to spontaneous pneumothorax. In our case, coronary angiography revealed non-obstructive coronary arteries, so the cause of chest pain was attributed to myocardial infarction with non-obstructive coronary arteries (MINOCA). Atypical causes of chest pain should be considered, especially in patients with diagnosed genetic syndromes.

Recommendations on scuba diving in Birt-Hogg-Dubé syndrome

INTRODUCTION

Although very uncommon, severe injury and death can occur during scuba diving. One of the main causes of scuba diving fatalities is pulmonary barotrauma due to significant changes in ambient pressure. Pathology of the lung parenchyma, such as cystic lesions, might increase the risk of pulmonary barotrauma.

AREAS COVERED

Birt-Hogg-Dubé syndrome (BHD), caused by pathogenic variants in the FLCN gene, is characterized by skin fibrofolliculomas, an increased risk of renal cell carcinoma, multiple lung cysts and spontaneous pneumothorax. Given the pulmonary involvement, in some countries patients with BHD are generally recommended to avoid scuba diving, although evidence-based guidelines are lacking. We aim to provide recommendations on scuba diving for patients with BHD, based on a survey of literature on pulmonary cysts and pulmonary barotrauma in scuba diving.

EXPERT OPINION

In our opinion, although the absolute risks are likely to be low, caution is warranted. Given the relative paucity of literature and the potential fatal outcome, patients with BHD with a strong desire for scuba diving should be informed of the potential risks in a personal assessment. If available a diving physician should be consulted, and a low radiation dose chest computed tomography (CT)-scan to assess pulmonary lesions could be considered.

Progression of pulmonary cysts in Birt-Hogg-Dubé syndrome: longitudinal thoracic computed tomography study with quantitative assessment

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disorder characterized by fibrofolliculomas, renal tumors, pulmonary cysts, and recurrent pneumothorax. Pulmonary cysts are the cause of recurrent pneumothorax, which is one of the most important factors influencing patient quality of life. It is unknown whether pulmonary cysts progress with time or influence pulmonary function in patients with BHD syndrome. This study investigated whether pulmonary cysts progress during long-term follow-up (FU) by using thoracic computed tomography (CT) and whether pulmonary function declines during FU. We also evaluated risk factors for pneumothorax in patients with BHD during FU.

METHODS

Our retrospective cohort included 43 patients with BHD (25 women; mean age, 54.2 ± 11.7 years). We evaluated whether cysts progress by visual assessment and quantitative volume analysis using initial and serial thoracic CT. The visual assessment included the size, location, number, shape, distribution, presence of a visible wall, fissural or subpleural cysts, and air-cuff signs. In CT data obtained from a 1-mm section from 17 patients, the quantitative assessment was performed by measuring the volume of the low attenuation area using in-house software. We evaluated whether the pulmonary function declined with time on serial pulmonary function tests (PFT). Risk factors for pneumothorax were analyzed using multiple regression analysis.

RESULTS

On visual assessment, the largest cyst in the right lung showed a significant interval increase in size (1.0 mm/year, p = 0.0015; 95% confidence interval [CI], 0.42-1.64) between the initial and final CT, and the largest cyst in the left lung also showed significant interval increase in size (0.8 mm/year, p < 0.001, 95% CI; -0.49-1.09). On quantitative assessment, cysts had a tendency to gradually increase in size. In 33 patients with available PFT data, FEV1pred%, FEV1/FVC, and VCpred% showed a statistically significant decrease with time (p < 0.0001 for each). A family history of pneumothorax was a risk factor for the development of pneumothorax.

CONCLUSIONS

The size of pulmonary cysts progressed over time in longitudinal follow-up thoracic CT in patients with BHD, and pulmonary function had slightly deteriorated by longitudinal follow-up PFT.

Lymphangioleiomyomatosis and Other Cystic Lung Diseases

Cysts and cavities in the lung are commonly encountered on chest imaging. It is necessary to distinguish thin-walled lung cysts (≤2 mm) from cavities and characterize their distribution as focal or multifocal versus diffuse. Focal cavitary lesions are often caused by inflammatory, infectious, or neoplastic processes in contrast to diffuse cystic lung diseases. An algorithmic approach to diffuse cystic lung disease can help narrow the differential diagnosis, and additional testing such as skin biopsy, serum biomarkers, and genetic testing can be confirmatory. An accurate diagnosis is essential for the management and disease surveillance of extrapulmonary complications.

Diseases of Hereditary Renal Cell Cancers

Germline mutations in tumor suppressor genes and oncogenes lead to hereditary renal cell carcinoma (HRCC) diseases, characterized by a high risk of RCC and extrarenal manifestations. Patients of young age, those with a family history of RCC, and/or those with a personal and family history of HRCC-related extrarenal manifestations should be referred for germline testing. Identification of a germline mutation will allow for testing of family members at risk, as well as personalized surveillance programs to detect the early onset of HRCC-related lesions. The latter allows for more targeted and therefore more effective therapy and better preservation of renal parenchyma.

Cigarette smoking is a secondary cause of folliculin loss

BACKGROUND

Birt-Hogg-Dubé syndrome (BHD) is a clinical syndrome manifesting with cystic lung disease and pneumothorax. Features of BHD result from the loss-of-function mutations of the folliculin (FLCN) gene. Chronic obstructive pulmonary disease (COPD), characterised by an irreversible airflow limitation, is primarily caused by cigarette smoking.

OBJECTIVE

Given that COPD often shares structural features with BHD, we investigated the link between COPD, cigarette smoke (CS) exposure and FLCN expression.

METHODS

We measured the expression of FLCN in human COPD lungs and CS-exposed mouse lungs, as well as in CS extract (CSE)-exposed immortalised human airway epithelial cells by immunoblotting.

RESULTS

We found that the lung FLCN protein levels in smokers with COPD and CS exposure mice exhibit a marked decrease compared with smokers without COPD and room air exposure mice, respectively. We confirmed CS induced degradation of FLCN in immortalised human bronchial epithelial Beas-2B cells via ubiquitin proteasome system. Further, siRNA targeting FLCN enhanced CSE-induced cytotoxicity. By contrast, FLCN overexpression protected cells from CSE-induced cytotoxicity. We found that FBXO23, the ubiquitin E3 ligase subunit, specifically binds to and targets FLCN for degradation. Inhibition of ATM (ataxia-telangiectasia mutated) attenuated CSE induced FLCN degradation, suggesting a role of ATM in FLCN proteolysis. We further confirmed that the mutant of major FLCN phosphorylation site serine 62A is resistant to CSE-induced degradation and cytotoxicity.

CONCLUSIONS

Our study demonstrates that CS exposure is a secondary cause of FLCN deficiency due to the enhanced proteolysis, which promoted airway epithelial cell death.

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.

Birt-Hogg-Dubé syndrome associated with chorioretinopathy and nyctalopia: a case report and review of the literature

PURPOSE

To report a rare case of Birt-Hogg-Dubé Syndrome (BHD) with progressive chorioretinopathy.

METHODS

Case report.

RESULTS

A 55-year-old woman presented with longstanding nyctalopia attributed to a congenital retinal dystrophy, but no prior genetic testing. Her posterior pole examination demonstrated retinal pigment epithelium (RPE) mottling with extensive macular drusen and paracentral chorioretinal atrophy, consistent with a fleck retinopathy. Her past medical history was remarkable for nephrectomy for unilateral renal malignancy, parotid tumors and thyroid nodules. Dark adaptation time was prolonged, and electroretinography (ERG) revealed abnormal waveforms with depressed amplitudes. Genetic testing confirmed a deletion mutation in the folliculin (FLCN) gene and was negative for other relevant mutations, including EFEMP1 responsible for autosomal dominant macular and peripapillary drusen in Doyne honeycomb retinal dystrophy and TIMP3 responsible for Sorsby Fundus Dystrophy.

CONCLUSION

BHD is a rare autosomal-dominant disorder with multi-systemic clinical manifestations caused by a mutation in the FLCN gene. Affected individuals are prone to renal and pulmonary cysts, renal cancer, and fibrofolliculomas. Reports on ocular manifestations of BHD include eyelid fibrofolliculomas, flecked chorioretinopathy, choroidal melanoma, choroidal melanoma with sector melanocytosis, and retinal pigment epithelial micro-detachments. In this case of BHD, we note a fleck retinopathy with bilateral chorioretinal atrophy, displaying a phenotype of extensive chorioretinopathy associated with impaired dark adaptation and ERG abnormalities.

ABBREVIATIONS

BHD: Birt-Hogg-Dubé syndrome; FLCN: Folliculin. RPE: retinal pigment epithelium; OD: Oculus dexter (right eye); OS: Oculus sinister (left eye). OU: Oculus uterque (both eyes); ERG: electroretinogram; mfERG: multifocal electroretinography. ffERG: full-field electroretinography; FAF: fundus autofluorescence; OCT: optical coherence tomography; FA: fluorescein angiography; DA: dark-adapted; LA: light-adapted; mTOR: mammalian target of rapamycin; EFEMP1: epithelial growth factor-containing fibulin-like extracellular matrix protein 1; VPS13B: Vacuolar Protein Sorting 13 Homolog B; AGBL5: AATP/GTP-Binding Protein Like 5; ALMS1: Alstrom Syndrome 1; COL1BA1: Collagen Type I Beta, Alpha Chain 1; PDE6A: Rod Phosphodiesterase 6-alpha; USH2A: Usherin 2a; VCAN: Versican; RP: Retinitis pigmentosa; AR: Autosomal recessive.

PRDM10 directs FLCN expression in a novel disorder overlapping with Birt-Hogg-Dubé syndrome and familial lipomatosis

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant disorder characterized by fibrofolliculomas, pulmonary cysts, pneumothoraces and renal cell carcinomas. Here, we reveal a novel hereditary disorder in a family with skin and mucosal lesions, extensive lipomatosis and renal cell carcinomas. The proband was initially diagnosed with BHD based on the presence of fibrofolliculomas, but no pathogenic germline variant was detected in FLCN, the gene associated with BHD. By whole exome sequencing we identified a heterozygous missense variant (p.(Cys677Tyr)) in a zinc-finger encoding domain of the PRDM10 gene which co-segregated with the phenotype in the family. We show that PRDM10Cys677Tyr loses affinity for a regulatory binding motif in the FLCN promoter, abrogating cellular FLCN mRNA and protein levels. Overexpressing inducible PRDM10Cys677Tyr in renal epithelial cells altered the transcription of multiple genes, showing overlap but also differences with the effects of knocking out FLCN. We propose that PRDM10 controls an extensive gene program and acts as a critical regulator of FLCN gene transcription in human cells. The germline variant PRDM10Cys677Tyr curtails cellular folliculin expression and underlies a distinguishable syndrome characterized by extensive lipomatosis, fibrofolliculomas and renal cell carcinomas.

Presentation and Management of a Novel Ehlers-Danlos COL5A1 Variant With Birt-Hogg-Dube Syndrome: A Case Study

Ehlers-Danlos syndrome (EDS) is a hereditary disorder caused by a mutation in the COL gene, which leads to the faulty synthesis of the collagen protein. EDS can present with a wide array of manifestations depending upon which COL gene is mutated. Birt-Hogg-Dubé (BHD) syndrome is a rare hereditary disorder currently identified in 200 families worldwide. It presents clinically with cutaneous, renal, and pulmonary manifestations due to an autosomal dominant mutation in a tumor suppressor gene, FLCN, on chromosome 17p11.2. We present a case of a 22-year-old male with Birt-Hogg-Dubé syndrome, showing typical features consistent with the classical type of EDS, with genetic testing revealing a COL5A1 mutation of "uncertain clinical significance", not yet reported in clinical literature. We discuss the treatment of this patient and describe the presentations of the two pathologies. Lastly, we put forth guidelines for the management of a dilated ascending aorta, with which this patient presents, for future patients who may present with this novel EDS mutation.

Oncocytic carcinoma of the parotid gland as a manifestation of Birt-Hogg-Dube syndrome

Renal oncocytomas are commonly reported in association with Birt-Hogg-Dube (BHS) syndrome, while BHD-associated oncocytomas of the parotid gland are rare. To date, there have been only 11 cases of BHD-associated parotid gland oncocytoma, without a reported case of malignant transformation. We present the first reported case of oncocytic carcinoma of the parotid gland associated with BHD, with radiologic and histologic correlation. This case establishes that BHD-associated parotid oncocytic lesions, previously identified only as benign oncocytomas in the literature to date, can undergo malignant transformation, and should potentially be regarded with a higher index of suspicion and lower threshold for aggressive management.

Minigene Assay as an Effective Molecular Diagnostic Strategy in Determining the Pathogenicity of Noncanonical Splice-Site Variants in FLCN

Primary spontaneous pneumothorax (PSP) or pulmonary cyst is one of the manifestations of Birt-Hogg-Dubé syndrome, which is caused by pathogenic variants in FLCN gene. Genetic testing in patients with PSP identifies a certain number of missense or intronic variants. These variants are usually considered as variants of uncertain significance, whose functional interpretations pose a challenge in clinical genetics. To improve recognition of pathogenic splice-altering variants in FLCN gene, computational tools are used to prioritize potential splice-altering variants and then a hybrid minigene assay is performed to verify the RNA splicing pattern. Herein, variants in FLCN exon 11 and its flanking sequence are focused. Eight variants detected in 11 patients with PSP are evaluated, and six variants are prioritized by in silico tools as potential splice-altering variants of uncertain significance. Four variants (c.1177-5_1177-3delCTC, c.1292_1300+4del, c.1300+4C>T, and c.1300+5G>A) are demonstrated by minigene assay to alter RNA splicing of FLCN, and the last three of them are novel. RT-PCR of patient-derived RNA gives consistent results. Genotype-phenotype correlation analysis in patients with PSP with these variants demonstrates good concordance. Our results underline the importance of RNA analysis, which could provide molecular evidence for pathogenicity of a variant, and provide essential information for the clinical interpretation of variants. Combining the clinical information, a definitive diagnosis could be made.

High-Resolution Computed Tomography of Cystic Lung Disease

The cystic lung diseases (CLD) are characterized by the presence of multiple, thin-walled, air-filled spaces in the pulmonary parenchyma. Cyst formation may occur with congenital, autoimmune, inflammatory, infectious, or neoplastic processes. Recognition of cyst mimics such as emphysema and bronchiectasis is important to prevent diagnostic confusion and unnecessary evaluation. Chest CT can be diagnostic or may guide the workup based on cyst number, distribution, morphology, and associated lung, and extrapulmonary findings. Diffuse CLD (DCLDs) are often considered those presenting with 10 or more cysts. The more commonly encountered DCLDs include lymphangioleiomyomatosis, pulmonary Langerhans' cell histiocytosis, lymphoid interstitial pneumonia, Birt-Hogg-Dubé syndrome, and amyloidosis/light chain deposition disease.

A novel FLCN gene mutation causing Birt-Hogg-Dubé syndrome in a Korean family

Spontaneous pneumothorax is a common manifestation of Birt–Hogg–Dubé (BHD) syndrome, an inherited disorder caused by mutation of the folliculin (FLCN) gene. A 44-year-old female with a history of breast cancer was diagnosed with recurrent pneumothorax. Chest CT showed multiple cysts with left lung pneumothorax, and she received surgery for the diagnosis. Because the patient also had a family history of spontaneous pneumothorax, a FLCN genetic examination was conducted. A novel heterozygous, likely pathogenic variant (NM_144997.5:c.779+2T > C) was detected in the proband, her mother, and aunt. This is the first report of a new mutation of FLCN gene in a BHD syndrome patient.

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.

Epidemiology and clinical features of Birt-Hogg-Dubé syndrome: A nationwide population-based study in South Korea

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is an ultrarare lung disease with unclear prevalence and incidence. Our study aimed to identify the epidemiological and clinical features of BHD syndrome by using nationwide claims data from the Korean Health Insurance Review and Assessment service.

METHODS

Patients with BHD syndrome who had the following criteria were included: 1) tested for folliculin gene mutation, and 2) had at least one of the conditions: other specified malformation syndromes, fibrofolliculoma, acrochordon, lung cyst, cancer, and pneumothorax based on International Classification of Disease-10 code.

RESULTS

We found 26 patients with BHD syndrome from 2017 to 2019. The prevalence of BHD syndrome was 5.67 per 107 population, with no peak age. Among incidence cases, the median age of diagnosis was 51 years, with slightly more females than males (n = 15, 57.7%). Over half of the patients (n = 14, 53.8%) experienced pneumothorax, and 10 (38.5%) developed malignant neoplasm within the clinical course.

CONCLUSIONS

The prevalence of BHD syndrome in Korea is extremely low. However, affected patients manifest several comorbidities, including malignant neoplasm and repetitive pneumothorax.

Clinical and Genetic Comparison of Birt–Hogg–Dubé Syndrome (Hornstein–Knickenberg Syndrome) in Chinese: A Systemic Review of Reported Cases

Background

Birt–Hogg–Dubé syndrome (BHD), also named Hornstein–Knickenberg syndrome, is a rare autosomal dominant disease characterized by lung cysts, recurrent pneumothoraxes, renal cell carcinoma and skin fibrofolliculomas.

Purpose

This study summarizes the clinical and genetic information of Chinese BHD patients from all available reported cases and explores the relationship between the clinical and genetic spectrum in the hope of improving the prognosis of Chinese BHD patients.

Methods

Relative studies were collected by searching PubMed, Cochrane Library, Embase, OVID medicine, SinoMed, Web of Science, China National Knowledge Infrastructure, Wanfang Data and China Hospital Knowledge Database from January 1, 1977 to December 31, 2021. The search strategy included the following term keys: (Birt–Hogg–Dubé syndrome OR Hornstein-Kinckenberg syndrome OR familial pulmonary cysts OR familial spontaneous pneumothorax OR fibrofolliculomas OR trichodiscomas OR inherited renal cancer syndromes OR FLCN) AND (Chinese OR China).

Results

In total, 287 Chinese patients from 143 families described in 31 references were included in this article. Chinese BHD patients tended to present more pulmonary symptoms but fewer skin lesions and renal malignancies, which appeared to be atypical when compared with Caucasian patients. The FLCN mutation spectrum among Chinese BHD patients was established with the mutational hot spot c.1285depC/delC as the most frequent mutation. In addition, this mutation spectrum also showed some differences from other races, with a relatively frequent large deletion c.872–429_1740+1763del (exon 9–14 deletion) reported only in Chinese individuals but no observation of the two mutational hot spots found in Japanese individuals. We also attempted to establish potential pheno-genotype correlations in Chinese BHD patients, but the results were negative.

Conclusion

To improve the prognosis of BHD patients, physicians need to increase their awareness of BHD by focusing on the family history of pneumothorax as well as skin lesions in patients with lung cysts and promptly advising patients on genetic sequencing.

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 holistic investigation of the global outcomes of spontaneous pneumothorax during 1980-2021, including the COVID-19 pandemic A bibliometric approach

BACKGROUND

During coronavirus pandemic, despite the increase in the number of studies on spontaneous pneumothorax (SP), there is not enough bibliometric study in the literature. In this study, it was aimed to analyze scientific articles published on SP.

METHODS

Studies published on SP between 1980 and 2021 were obtained from the Web of Science database and analyzed using statistical and bibliometric methods. Spearman correlation coefficient was used for correlation studies. The exponential smoothing estimator was used to forecast publication trend for coming years. Network visualization maps were used to analyze citations and identify trending topics.

RESULTS

A total of 2422 publications were found. 1403 (57.9%) of these publications were articles. The articles on SP have increased with a non-linear trend in recent years. The top 5 contributors to the literature were USA (231, 16.4%), Japan (161, 11.4%), United Kingdom (98, 6.9%), France (81, 5.7%), and Taiwan (78, 5.5%). The top 3 most active institutions were National Taiwan University Hospital (22, 1.5%), Catholic University Korea (19, 1.3%), and National Taiwan University (19, 1.3%). The top 3 journals that published the most articles were Chest (51), Annals of Thoracic Surgery (46), and Journal of Thoracic Disease (45). The most studied subjects were primary SP, recurrence, thoracoscopy, pleurodesis, video-assisted thoracoscopic surgery, COVID-19, video-assisted thoracic surgery, chest tube(s), and secondary spontaneous pneumothorax. According to trend topics analysis, the keywords studied in recent years are COVID-19, chest tubes, pneumonia, subcutaneous emphysema, risk factors, dyspnea, primary SP, FLCN gene, tension pneumothorax, uniportal, postoperative recurrence, secondary spontaneous pneumothorax, chronic obstructive pulmonary disease, and uniportal.

CONCLUSION

In this comprehensive bibliometric study, we summarized 1403 articles about SP, which has an increasing trend in the number of articles during the COVID-19 pandemic process. This article can be a useful resource for clinicians and scientists through presenting a summary of worldwide studies related to SP, including the ones during COVID-19 pandemic.

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.

Correlative analysis of lung CT findings in patients with Birt–Hogg–Dubé Syndrome and the occurrence of spontaneous pneumothorax: a preliminary study

Background

The diagnosis of patients with Birt–Hogg–Dubé (BHD) syndrome is always delayed (even for more than 10 years). Improving the understanding and diagnosis of this disease is vital for clinicians and radiologists. In this study we presented the chest computed tomography (CT) findings of BHD syndrome and offered suggestions for BHD cases with spontaneous pneumothorax.

Methods

Twenty-six BHD patients from 11 families (10 men, 16 women; mean age: 46 ± 12 years, 20–68 years) were included. The clinical features of the patients included pneumothorax, renal lesions, and skin lesions. Twenty-three patients underwent chest CT imaging. The cyst condition of each patient derived from reconstructed chest CT imaging was recorded, including the cyst number, size, volume, pattern, and distribution.

Results

Pneumothorax occurred in 54% (14/26) of patients. Among them, 43% (6/14) had pneumothorax more than twice. However, typical skin and renal lesions were absent. Four patients had renal hamartoma. CT showed that 23 (100%) patients had lung cysts. Pulmonary cysts were bilateral and multiple, round, irregular, or willow-like. And 93.6% of the large cysts (long-axis diameter ≥ 20 mm) were under the pleura, and near the mediastinum and spine. The long-axis diameter, short-axis diameter and volume of the largest cysts were associated with the occurrence of pneumothorax (all P < 0.05).

Conclusions

Chest CT imaging can reveal some characteristic features of BHD syndrome. The occurrence of pneumothorax in BHD patients is closely related to their pulmonary cystic lesions.

Seventh BHD international symposium: recent scientific and clinical advancement

The 7th Birt-Hogg-Dubé (BHD) International Symposium convened virtually in October 2021. The meeting attracted more than 200 participants internationally and highlighted recent findings in a variety of areas, including genetic insight and molecular understanding of BHD syndrome, structure and function of the tumor suppressor Folliculin (FLCN), therapeutic and clinical advances as well as patients' experiences living with this malady.

Birt-Hogg-Dubé Syndrome: Diagnostic Journey of Three Cases from Skin to Gene

Birt-Hogg-Dube syndrome (BHDS) is a rare disorder characterized by the triad of cutaneous lesions, renal tumors, lung cysts and inactivation of the gene folliculin (FLCN). Here, we present three female patients diagnosed with BHDS. First case a 55-year-old female had flesh moles histopathology compatible with angiofibroma, multiple cysts in the lung and kidneys, FLCN gene mutations (‘c.1285dupC [p.His429Profs*]’ 11th exon and ‘c.653G>A [p.Arg258His]’ 7th exon). The second case a 76-year-old female had trichodiscoma on her skin, multiple cysts in the lung, spontaneous pneumothorax, FLCN gene mutation ‘c.1285dupC (p.His429Profs*27) 11th exon’ and, her son had renal carcinoma history under 50 years of age. Our third case, also the daughter of case 2, had dermal papules histopathology compatible with trichodiscoma, spontaneous pneumothorax, FLCN gene mutation ‘c.1285dupC (p.His429Profs*27) 11th exon’ and, parotid oncocytoma. Through our cases, we document the first case of two mutations (‘c.1285dupC [p.His429Profs*]’ 11th exon and ‘c.653G>A [p.Arg258His]’ 7th exon) in the same FLCN gene and the 11th known case of parotid oncocytoma associated with BHDS in the light of the literature.

Renal and Lung Cysts in Birt-Hogg-Dubé Syndrome: A Continuum of the Same Disorder

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal-dominant disorder, affecting multiple organs, mostly the skin, lungs, and kidneys. The prevalence of BHD syndrome is difficult to define given the rarity of the disease. Patients present most often with primary spontaneous pneumothorax. Renal tumors are a characteristic finding in BHD, and are often bilateral and multifocal and of the chromophobe and oncocytoma variant. Very scarce reports have highlighted the presence of simple renal cysts, as the only phenotypical renal manifestation, in BHD patients. Herein, we highlight two novel cases of bilateral multiple renal and pelvic cysts, in two females with genetically proven BHD syndrome, doubting a potential association with BHD syndrome.

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

Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal-dominant multiorgan systemic disorder manifesting as cutaneous fibrofolliculomas, lung cysts with or without spontaneous pneumothorax, and renal tumors. It results from mutation of the gene located on the short arm of chromosome 17 (17p11.2). The gene codes for the protein folliculin, which is believed to be an oncogene suppressor protein. This syndrome is often underdiagnosed. Presence of lung cysts on chest CT should prompt inclusion of BHDS in the differential diagnosis, since these findings may develop earlier than other manifestations. There are key imaging characteristics of pulmonary cysts on CT of the chest which can suggest the diagnosis of BHDS and help in early detection and prompt screening for renal tumors. The main concern with BHDS is the increased risk of renal carcinoma. Here, we report a case of a 59-year-old male who was suspected to have the diagnosis of BHDS based on characteristic features of lung cysts on the Chest CT, subsequently confirmed by genetic testing.