Birt-Hogg-Dube syndrome prospectively detected by review of chest computed tomography scans

Outstanding Characteristics of Birt-Hogg-Dube Syndrome in Korea

Birt-Hogg-Dube (BHD) is a rare genetic disorder characterized by multiple lung cysts, typical skin manifestations, and renal tumors. We prospectively enrolled thirty-one subjects from four South Korean institutions with typical lung cysts, and next-generation sequencing was conducted. We prospectively enrolled thirty-one subjects from four Korean institutions with typical lung cysts. Next-generation sequencing was performed to investigate mutations in the following genes: FLCN, TSC1, TSC2, CFTR, EFEMP2, ELN, FBLN5, LTBP4, and SERPINA1. BHD was diagnosed in 11 of the 31 enrolled subjects (35.5%; FLCN mutations). Notably, we identified three novel mutations (c.1098G>A, c.139G>T, and c.1335del) that have not been previously reported. In addition to FLCN mutations, we also observed mutations in CFTR (16.1%), LTBP4 (9.7%), TSC2 (9.7%), TSC1 (3.2%), ELN (3.2%), and SERPINA1 (3.2%). According to a systematic review of 45 South Korean patients with BHD, the prevalence of pneumothorax (72.7%) was greater in South Korea than in the rest of the world (50.9%; p = 0.003). The prevalence of skin manifestations (13.6%) and renal tumors (9.1%) was lower in Korea than in the rest of the world, at 47.9% [p < 0.001] and 22.5% [p = 0.027], respectively). This study confirmed a significant prediction model for BHD based on age, number of lung cysts (>40), and maximal diameter of lung cysts (>2 cm) regardless of skin manifestations and renal tumors. Importantly, three novel mutations (c.1098G>A, c.139G>T, and c.1335del) were identified. In conclusion, South Korean patients with BHD display characteristics that are different from those observed in patients of other nationalities. Detailed characterization of lung cysts is needed to define BHD, especially in South Korea, even if patients do not present with skin or renal lesions.

Characteristic Chest Computed Tomography Findings for Birt-Hogg-Dube Syndrome Indicating Requirement for Genetic Evaluation

Background: Chest computed tomography (CT) findings are important for identifying Birt−Hogg−Dube (BHD) syndrome. However, the predictive power of classical criteria for chest CT findings is weak. Here, we aimed to identify more specific chest CT findings necessitating genetic examination for FLCN gene mutations. Methods: From June 2016 to December 2017, we prospectively enrolled 21 patients with multiple bilateral and basally located lung cysts on chest CT with no other apparent cause, including cases with and without spontaneous primary pneumothorax. All enrolled patients underwent FLCN mutation testing for diagnosis confirmation. Results: BHD was diagnosed in 10 of 21 enrolled patients (47.6%). There were no differences in clinical features between the BHD and non-BHD groups. Maximal cyst diameter was significantly greater in the BHD group (mean ± standard deviation; 4.1 ± 1.1 cm) than in the non-BHD group (1.6 ± 0.9 cm; p < 0.001). Diversity in cyst size was observed in 100.0% of BHD cases and 18.2% of non-BHD cases (p = 0.001). Morphological diversity was observed in 100.0% of BHD cases and 54.6% of non-BHD cases (p = 0.054). Areas under the receiver operating characteristic curves for predicting FLCN gene mutations were 0.955 and 0.909 for maximal cyst diameter and diversity in size, respectively. The optimal cut-off value for maximal diameter FLCN mutations prediction was 2.1 cm (sensitivity: 99%; specificity: 82%). Conclusions: Reliable chest CT features suggesting the need for FLCN gene mutations screening include variations in cyst size and the presence of cysts > 2.1 cm in diameter, predominantly occurring in the bilateral basal lungs.

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.

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.

Clinical Characteristics and Genetic Analysis of a Family With Birt-Hogg-Dubé Syndrome and Congenital Contractural Arachnodactyly

Background: Birt-Hogg-Dubé (BHD) syndrome and congenital contractural arachnodactyly (CCA) or Beals-Hecht syndrome are clinically rare autosomal dominant genetic diseases. In this study, we describe an extremely rare family with BHD syndrome and CCA.

Objective: To investigate the clinical and genetic characteristics of a family with BHD syndrome and CCA.

Methods: We describe the clinical characteristics, family history, and clinical manifestations of the patient’s family members. The patient underwent a blood test, computed tomography (CT) of the chest, color Doppler ultrasound of the abdomen and heart, and digital radiography of the hands. Whole exome sequencing was performed on his family members.

Results: Two years ago, the male proband developed chest tightness and shortness of breath that was accompanied by an irritating cough as well as repeated (four times) spontaneous pneumothorax. The chest CT indicated spontaneous pneumothorax on the right side and cyst and bullae in both lungs. He had no kidney tumors or skin lesions. His son had a history of pulmonary bullae and experienced spontaneous pneumothorax twice. The proband, his mother, and his son were all born with a hand deformity. The sequencing results demonstrated that both the proband and his son had heterozygous variations of the folliculin (FLCN) gene c.1015C > T (p. Gln339Ter) and fibrillin-2 (FBN2) gene c.3485G > A (p. Cys1162Tyr), which are associated with BHD syndrome and CCA, respectively.

Conclusion: For patients with chest tightness, shortness of breath, recurrent spontaneous pneumothorax, and congenital hand deformity without inducement, genetic testing should be carried out as soon as possible to make a clear diagnosis, which can then guide treatment and genetic counseling.

Birt-Hogg-Dubé syndrome in Chinese patients: a literature review of 120 families

Objective

To clarify the epidemiological and clinical features of Birt–Hogg–Dubé syndrome (BHDS) in Chinese patients.

Methods

We identified reports on Chinese patients with BHDS by searching the China Academic Journals Database, Wanfang Chinese Database, and PubMed databases, either in Chinese or English languages published from January 1, 2008 to December 31, 2020. Studies without sufficient clinical data were excluded and cases under 18 years old were excluded.

Results

Twenty papers were included and comprised 120 families with 221 cases. Most families with BHDS were reported from institutions in Beijing (66.7%) and Jiangsu Province (15.8%); 80.8% of cases were reported within the past five years. The average duration from clinical presentation to diagnosis was 9.6 years. The average age was 47.0 ± 13.9 years (range, 18–84 years) and the ratio of male to female was 1:1.6. The most common manifestations of BHDS were multiple pulmonary cysts (92.4%), spontaneous pneumothorax (71.0%), skin lesions (18.1%) and renal tumors (3.6%). Pulmonary cysts were predominantly distributed in the lower lobe on chest CT imaging. Family history of spontaneous pneumothorax was identified in 84.7% of the families and average number of pneumothoraxes was 1.8 (range, 1–6). The FLCN gene mutation c.1285dupC/delC in exon 11 was the most frequent mutation observed (17.4% of patients). The recurrence rate of pneumothorax after conservative treatment (including tube thoracostomy) was 29/41 (71%) while the pneumothorax recurred after surgical treatment (pulmonary bullectomy or pleurodesis) in only 4/37 (11%).

Conclusions

Although BHDS has been increasingly reported in the recent years, only minority of families were reported from institutions outside of Beijing and Jiangsu Province. The dominant clinical manifestations were pulmonary cysts associated with recurrent pneumothorax, while skin lesions and renal tumors were less commonly reported. Delayed diagnosis along with suboptimal management appear to represent critical challenges for Chinese patients with BHDS.

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

Characterization of CT scans of patients with Birt-Hogg-Dubé syndrome compared with those of Chinese patients with non-BHD diffuse cyst lung diseases

Background and objective

The purpose of this study was to create a practical CT-based algorithm to differentiate Birt-Hogg-Dubé (BHD) syndrome from other diffuse cystic lung diseases (DCLD).

Methods

The study was a retrospective review of the CT images of 33 patients with BHD syndrome, 33 patients with LAM, and 23 patients with NBNL (non-BHD and non-LAM) among DCLD patients. On the basis of the data collected, the CT images were reviewed again to evaluate the characteristics (size, number, distribution, and morphology) of pulmonary cysts.

Results

Lower lung-predominant cysts were more likely to be found in patients with BHD syndrome than in patients with LAM or in the NBNL DCLD group. In the axial distribution, 18 of 33 patients in BHD group had cysts that were predominantly near the mediastinum, and all the patients in the LAM and NBNL DCLD groups had diffuse cysts. The appearance of fusiform cysts was more easily observed in patients in the BHD group. In total, 58% patients in the BHD group had less than 50 lung cysts, while all patients in the non-BHD group had more than 50 lung cysts. The biggest cyst was located in the lower lobe in 28 of 33 patients in the BHD group, while 11 of 33 patients in LAM group and 10 patients in the NBNL DCLD group had the biggest cyst in the lower lobe.

Conclusion

The pulmonary cysts in patients with BHD tended to be fusiform, less numerous and located predominantly in the lower lobe and near the mediastinum. These radiologic pulmonary features could assist physicians in differentiating BHD from other DCLDs.

FLCN-regulated miRNAs suppressed reparative response in cells and pulmonary lesions of Birt-Hogg-Dubé syndrome

Background

Birt-Hogg-Dubé Syndrome (BHDS) characterised by skin fibrofolliculomas, kidney tumour and pulmonary cysts/pneumothorax is caused by folliculin (FLCN) germline mutations. The pathology of both neoplasia and focused tissue loss of BHDS strongly features tissue-specific behaviour of the gene. Isolated cysts/pneumothorax is the most frequent atypical presentation of BHDS and often misdiagnosed as primary spontaneous pneumothorax (PSP). Deferential diagnosis of BHDS with isolated pulmonary presentation (PSP-BHD) from PSP is essential in lifelong surveillance for developing renal cell carcinoma.

Methods

The expression profiles of microRNAs (miRNAs) in cystic lesions of PSP-BHD and PSP were determined via microarray. The selected upregulated miRNAs were further confirmed in the plasma of an expanded cohort of PSP-BHD patients by reverse transcription quantitative PCR (RT-qPCR). Their diagnostic accuracy was evaluated. Moreover, the cellular functions and targeted signalling pathways of FLCN-regulated miRNAs were assessed in various cell lines and in the lesion tissue contexts.

Results

Cystic lesions of PSP-BHD and PSP showed different miRNAs profiles with a significant upregulation of miR-424–5p and let-7d-5p in PSP-BHD. The combination of the two effectively predicted BHDS patients. In vitro studies revealed a suppressive effect of FLCN on miR-424–5p and let-7d-5p expressions specifically in lung epithelial cells. The ectopic miRNAs triggered epithelial apoptosis and epithelial transition of mesenchymal cells and suppressed the reparative responses in cells and tissues with FLCN deficiency.

Conclusion

The upregulation of miR-424–5p and let-7d-5p by FLCN deficiency occurred in epithelial cells and marked the PSP-BHD condition, which contributed to a focused degenerative pathology in the lung of PSP-BHD patients.

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.

Role of Radiologists in the Diagnosis of Unsuspected Birt-Hogg-Dubé Syndrome in a Tertiary Clinical Practice

OBJECTIVE. Birt-Hogg-Dubé (BHD) syndrome is considered rare. Growing evidence indicates that it is underdiagnosed. The purpose of this study is to ascertain the impact of radiology reports that suggest the possibility of BHD syndrome on downstream management and a final diagnosis of BHD syndrome. MATERIALS AND METHODS. In this retrospective study, electronic medical records were searched to identify radiology reports suggesting the possibility of BHD syndrome in patients without a known or suspected diagnosis. Clinical and demographic information, the specialty of the ordering clinician, and imaging findings and confidence conveyed in the radiology report (with BHD syndrome listed as the most likely diagnosis versus one among several possibilities but not as the leading diagnosis) were recorded. The resultant downstream evaluations that were captured included referral for genetic evaluation and subsequent diagnosis of BHD. RESULTS. Between 2004 and 2016, radiologists suggested a diagnosis of BHD syndrome in 87 patients. Of these patients, 15% (13/87) underwent genetic evaluation, and 54% of those patients (7/13) had positive findings. Genetic evaluation was more likely for patients with a history of pneumothorax (p = 0.004) or involvement of the lungs and kidneys (p = 0.003). The urology department referred the highest percentage of patients (31% [4/13]) for genetic evaluation. CONCLUSION. Radiologists have a unique opportunity to suggest BHD syndrome, allowing appropriate genetic testing, screening, and counseling of patients and their families. Clinical presentation, including a history of pneumothorax and involvement of both the lungs and kidneys on imaging, may determine which patients are ultimately referred for genetic evaluation. We hope that increasing awareness that BHD syndrome is not so rare may lead to early diagnosis.

Differentiation Between Lymphangioleiomyomatosis and Birt-Hogg-Dubé Syndrome: Analysis of Pulmonary Cysts on CT Images

OBJECTIVE

The purposes of this study were to identify diagnostic imaging markers for differentiating pulmonary cysts in lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome and to identify potential risk factors for spontaneous pneumothorax in the two diseases.

MATERIALS AND METHODS

This retrospective study included 44 patients with lymphangioleiomyomatosis (44 women; mean age, 35 ± 10.9 years) and 13 patients with Birt-Hogg-Dubé syndrome (nine men, four women; mean age, 45.1 ± 10.9 years). CT findings were analyzed to determine the shape; presence of septation, wall visibility, and subpleural cysts; size; number; distribution; location of the largest cyst; and presence of cysts encircling the bronchovascular bundle ("air-cuff" sign) and of mediastinal fat indentation. Multiple logistic regression was performed to identify risk factors for spontaneous pneumothorax.

RESULTS

Compared with patients with lymphangioleiomyomatosis, patients with Birt-Hogg-Dubé syndrome were significantly older, and more of them were men. The cysts in these patients had a more irregular shape, more septation, lower and more peripheral distribution, larger maximum size, and more attachment to the pleura, air-cuff sign, indentation on mediastinal fat, and subpleural cysts larger than 2 cm. The maximum diameter of cysts was the sole independent risk factor for spontaneous pneumothorax (p = 0.027; 95% CI, 1.043-1.992) in both diseases. ROC analysis showed an AUC of 0.745 (95% CI, 0.612-0.851), and the optimal cutoff value was 22 mm (sensitivity, 72.5%; specificity, 76.5%).

CONCLUSION

Several CT imaging markers may help in differentiating pulmonary cysts in patients with lymphangioleiomyomatosis and those with Birt-Hogg-Dubé syndrome and in predicting spontaneous pneumothorax.

Performance of sparse-view CT reconstruction with multi-directional gradient operators

To further reduce the noise and artifacts in the reconstructed image of sparse-view CT, we have modified the traditional total variation (TV) methods, which only calculate the gradient variations in x and y directions, and have proposed 8- and 26-directional (the multi-directional) gradient operators for TV calculation to improve the quality of reconstructed images. Different from traditional TV methods, the proposed 8- and 26-directional gradient operators additionally consider the diagonal directions in TV calculation. The proposed method preserves more information from original tomographic data in the step of gradient transform to obtain better reconstruction image qualities. Our algorithms were tested using two-dimensional Shepp–Logan phantom and three-dimensional clinical CT images. Results were evaluated using the root-mean-square error (RMSE), peak signal-to-noise ratio (PSNR), and universal quality index (UQI). All the experiment results show that the sparse-view CT images reconstructed using the proposed 8- and 26-directional gradient operators are superior to those reconstructed by traditional TV methods. Qualitative and quantitative analyses indicate that the more number of directions that the gradient operator has, the better images can be reconstructed. The 8- and 26-directional gradient operators we proposed have better capability to reduce noise and artifacts than traditional TV methods, and they are applicable to be applied to and combined with existing CT reconstruction algorithms derived from CS theory to produce better image quality in sparse-view reconstruction.

Delayed diagnosis of Birt-Hogg-Dubé syndrome due to marked intrafamilial clinical variability: a case report

Background

Birt-Hogg-Dubé syndrome is a genetic syndrome caused by mutations in the FLCN gene. The main symptoms are lung bullae and pneumothorax, benign and malignant kidney tumors, and facial fibrofolliculoma. The risk of pneumothorax is considerable between ages 20–40 years, but decreases markedly after this age range and first-time pneumothorax after age 50 years is rare. Fibrofolliculomas usually occur between ages 35 and 45 years, while the risk for kidney cancer increases steadily with age, starting in young adulthood. However, we demonstrate here that within the same family patients might develop symptoms significantly before or after the usual age range, obscuring the typical clinical pattern and delaying diagnosis.

Case presentation

The 43 year old index patient had a history of lung bullae and recurrent pneumothoraces starting 14 years earlier. His father (age 83 years) and one of the paternal uncles experienced their first pneumothorax unusually late after the age of 60 years. The uncle subsequently had four more pneumothoraces, and was diagnosed with kidney in his early 70s. Considerable differences in age of onset were also observed with regard to facial fibrofolliculomas that both paternal uncles developed very early around age 20 years, but which the father only started to show in his eighth decade. Birt-Hogg-Dubé syndrome was finally diagnosed when the index patient started to develop fibrofolliculomas within the typical age range.

Conclusions

The family described here illustrates that Birt-Hogg-Dubé syndrome can be difficult to recognize, if presenting with considerable intrafamilial clinical variability. With a life-time kidney cancer risk of about 14–35% the consequences of delayed diagnosis might be grave for the affected family members. The possibility of Birt-Hogg-Dubé syndrome should therefore be taken into consideration in apparently sporadic patients presenting with lung bullae and pneumothorax.

Birt-Hogg-Dubé syndrome: characteristic CT findings differentiating it from other diffuse cystic lung diseases

Birt-Hogg-Dubé (BHD) syndrome is an uncommon, autosomal dominant, multiorgan systemic disorder manifesting as cutaneous fibrofolliculomas, lung cysts with or without spontaneous pneumothorax, and renal tumors. Spontaneous pneumothorax and lung cysts on chest computed tomography (CT) should lead to the inclusion of BHD syndrome in the differential diagnosis, because these findings may develop earlier than other clinical manifestations. Here, we review and describe the characteristic findings of BHD syndrome. The number, shape, size, and distribution of the lung cysts can help to differentiate BHD syndrome from other diffuse cystic lung diseases. Knowledge of the chest CT findings of BHD syndrome may lead to a correct diagnosis and the initiation of an appropriate work-up in order to prevent pneumothorax and for the early detection of renal tumors.

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.