Chest CT in patients with spontaneous pneumothorax is cost-effective

Patients that present with a spontaneous pneumothorax (SP) without a known medical history of lung disease are usually diagnosed as primary spontaneous pneumothorax – a pneumothorax that occurs without underlying diseases. However, underlying diffuse cystic lung diseases such as Birt-Hogg-Dube syndrome (BHD), lymphangioleiomyomatosis (LAM) and pulmonary Langerhans cell histiocytosis (PLCH) may have a spontaneous pneumothorax as their first symptom. In their new study, Gupta et al. (2016) evaluate the cost-effectiveness of high resolution computed tomographic (HRCT) chest imaging for early diagnosis of LAM, BHD, and PLCH in patients presenting with an apparent primary SP. In their analysis the authors show that HRCT image screening for BHD, LAM and PLCH in patients with apparent primary SP is cost-effective and suggest that clinicians should consider performing a screening HRCT in these patients.

Even though an expert radiologist can very accurately diagnose PLCH, LAM, and BHD based on HRCT analysis alone (Gupta et al., 2015), routine CT chest imaging is not currently recommended in patients presenting with a spontaneous pneumothorax (Baumann et al., 2001). The authors compared using HRCT screening followed by pleurodesis in patients with LAM, BHD, or PLCH versus conventional management of SP with no HRCT screening. The authors used a Markov state-transition model to analyse decision trees and concluded that a strategy using HRCT screening for BHD, LAM and PLCH was cost-effective with a marginal cost-effectiveness ratio of $1,427 per quality adjusted life year (QALY) gained. In their base case analysis, authors attributed a diffuse cystic lung diseases prevalence of 8% among patients presenting with apparent primary SP (5% attributed to BHD, 2.5% to LAM, and 0.5% to PLCH based on literature). As expected, the strategy of HRCT screening became more cost-effective as the prevalence of LAM, BHD, or PLCH among patients presenting with an apparent primary SP increased. HRCT screening remained cost-effective for diffuse cystic lung diseases prevalence as low as 0.01% and below this value the strategy remained more effective but associated with increased cost. Again, as expected, as the ability to diagnose diffuse cystic lung diseases based on HRCT features increased, screening with HRCT became increasingly cost-effective. Primary spontaneous pneumothorax is mostly seen in young patients and secondary spontaneous pneumothorax is seen mainly in elderly patients (Gupta et al., 2000). The median age for development of pneumothorax is 38, 35, and 29 years for BHD, LAM, and PLCH, respectively, yet it is important to note that pneumothoraces also occur in older patients with diffuse cystic lung diseases (Mendez et al., 2004; Toro et al., 2007; Almoosa et al., 2006). Although it is common in elderly patients presenting with a SP to consider an underlying lung disease and perform CT imaging, in younger patients the diagnosis of primary spontaneous pneumothorax is often made without considering an underlying disease or performing CT imaging even though the age range of first pneumothorax in patients with a diffuse cystic lung disease overlaps with that of primary spontaneous pneumothorax. Authors did not perform analysis based on age distribution, however their results indicate that the strategy of HRCT screening remains cost-effective at any disease prevalence above 0.01%, which would very likely be the case for diffuse cystic lung diseases in any age group. Therefore, authors suggest that patients of all ages with an apparent primary SP should undergo a screening HRCT exam to check for the presence of underlying diffuse cystic lung diseases.

In addition to the benefit of early diagnosis of diffuse cystic lung diseases derived from early pleurodesis and prevention of recurrent pneumothoraces, the early diagnosis of LAM, BHD, and PLCH provides other potential benefits. For instance, early detection of BHD would allow patients to be regularly surveilled, allowing for early detection of renal cancer. In addition, identifying the index case of BHD in a family can also allow for screening of asymptomatic family members for the disease. Similarly, early detection of LAM or PLCH can facilitate disease management.

The study has a few limitations acknowledged by the authors such as the assumption in their model that all patients with LAM, BHD, and PLCH will agree to undergo pleurodesis and that all patients with an uncertain diagnosis will agree to have confirmatory testing for diffuse cystic lung diseases. Also, authors used Medicare data as a proxy for costs, so their conclusions may not be valid internationally.

In summary authors showed that HRCT screening for BHD, LAM and PLCH in patients with apparent primary spontaneous pneumothorax is cost-effective and suggest that clinicians should consider applying this strategy so that early diagnosis of diffuse cystic lung diseases can lead to appropriate management approaches.

  • Gupta N, Langenderfer D, McCormack FX, Schauer DP, & Eckman MH (2016). Chest Computed Tomographic Image Screening for Cystic Lung Diseases in Patients with Spontaneous Pneumothorax is Cost-effective. Annals of the American Thoracic Society PMID: 27737563

Cilia Conference 2016

The EMBO conference on Cilia 2016, ‘from fundamental biology to human disease’ was held last week over four days in Amsterdam, The Netherlands. The conference brought together ciliopathy patients, clinicians, and researchers to promote collaboration, create awareness and to discuss the latest developments in research of cilia and ciliopathies.

Cilia are microtubule-based organelles that protrude from the cell surface. There are different cilia categories including primary (non-motile) cilia and motile cilia. Primary cilia are the most common and function as sensory organelles. Motile cilia beat in a wave-like pattern and are mostly involved in generating fluid flow (Roy, 2009). Cilia defects cause ciliopathies which are diseases particularly associated with cyst formation in several organs, including kidneys (Hildebrandt et al., 2011).

BHD syndrome is considered a ciliopathy.  FLCN has been shown to localise to primary and motile cilia and to regulate ciliogenesis initiation (Luijten et al. 2013).  It has been shown to affect Wnt signalling and regulate mTORC1 by recruiting LKB1 to primary cilia, which leads to AMPK activation (Zhong et al. (2016).  Classifying BHD as a ciliopathy and further characterising FLCN’s role in ciliogenesis may help understand the pathogenesis of BHD and to identify a treatment to prevent cyst formation.

The Cilia conference included hundreds of oral and poster presentations highlighting:

  • Clinical aspects of ciliopathies – including the very common kidney manifestations, novel gene mutations that induce ciliopathies, molecular tools to resolve the spectrum of ciliopathies (Dr Hannah Mitchison), lethal ciliopathies (Dr Tania Attie-Bitach), synergic effects of mutations and mutations in Wnt-pathway genes that cause ciliopathies.
  • Signalling and development – including presentations on the molecular mechanisms underlying the activity of proteins involved in the formation of cilia, the role of primary cilia in the developmental of progenitor cells, the left-right organizer (LRO) and ciliopathy proteins controlling autophagy via the mTOR pathway (Andreas Struchtrup).
  • Ciliogenesis and transport – including several talks on intraflagellar transport dynamics.
  • Centrioles and basal bodies – including talks on centrosome cycle, cilia assembly and polarity and on the 3D structure of basal bodies (Dr Takashi Ishikawa)
  • Cilium structure and organization – including the solving of structures of the molecular machinery that shuttles and sorts the membrane-associated, lipid-modified, protein to the cilium (Dr Shehab Ismail), protein-protein interactions in the cilia and the role of post-translational modifications in cilia.
  • Translational therapeutics – with presentations with several mouse models that give more insight into the pathogenesis and genetic mechanisms of ciliopathies which allow for preclinical testing of new therapies (Dr Dorien J. M. Peters) and gene therapeutic approaches to correct mutations in ciliopathies.

The conference also integrated a patient perspective with a talk from Tess Harris from the Ciliopathy Alliance sharing her top tips for patient/public involvement in research. Dr Heymut Omran and Dr Nine Knoers gave a talk about European Reference Networks for rare diseases. There was also a Meet & Greet ciliopathy patients and patient groups event to promote networking between researchers and patients.

Even though there were no specific talks or posters about BHD syndrome or FLCN, several talks were relevant for BHD research either due to the similarity of symptoms with other ciliopathies or the involvement of similar pathways such as the mTOR pathway or the Wnt signalling pathway. Ultimately, the study of BHD will certainly benefit from the very intense research effort on ciliopathies that was clear during the entire conference.

This rapidly developing field is attracting an increasing amount of interest and two other Cilia conferences are already scheduled for 2017:

Cilia & Centrosomes – Suzhou, China, April 24-28

EMBO Cilia 2017 – Copenhagen, Denmark, date TBC

We will soon update the Conferences and Events page on with the 2017 forthcoming meetings that are relevant to BHD research.

  • Luijten, M., Basten, S., Claessens, T., Vernooij, M., Scott, C., Janssen, R., Easton, J., Kamps, M., Vreeburg, M., Broers, J., van Geel, M., Menko, F., Harbottle, R., Nookala, R., Tee, A., Land, S., Giles, R., Coull, B., & van Steensel, M. (2013). Birt-Hogg-Dube syndrome is a novel ciliopathy Human Molecular Genetics, 22 (21), 4383-4397 DOI: 10.1093/hmg/ddt288

Highlights from the RLDC 2016 Cincinnati Conference

As mentioned in last week’s blog, the International Rare Lung Diseases Research Conference (RLDC) was held in Cincinnati, USA, 22nd-25th September. Clinicians, scientists, patient organizations, patients and families were brought together to discuss research and clinical trials in rare lung disease and to promote dialogue between the research community and patients.

It is increasingly clear that some rare diseases share characteristics both in symptoms and underlying pathogenesis. Birt-Hogg-Dubé (BHD) syndrome is an example of this, sharing pulmonary, kidney and skin symptoms with a variety of other rare conditions. It is therefore important to stay informed about other rare conditions to avoid misdiagnosis and to understand that promoting research and trials in one rare disease may help the research development and the treatments of others.

Dr David Fajgenbaum from the University of Pennsylvania was responsible for the kick-off presentation. He shared his story of battling multicentric Castleman disease (MCD) as a physician-scientist-advocate-patient. In 2012 Dr Fajgenbaum funded the Castleman Disease Collaborative Network (CDCN) to connect the community of patients and researchers and to accelerate research in CD. Since then a lot has advanced in CD research with new models and treatment approaches (Fajgenbaum et al., 2016). Dr Fajgenbaum emphasized the importance of questioning the status quo and of collaboration among all stakeholders.

The FDA presented their work collaboration with the LAM foundation in the approval of Sirolimus treatment and their programs to help develop drugs in the rare disease field. There were several presentations about the current state of the art diagnostics and treatments for rare lung diseases:

  • Dr Denise Adams from Harvard Medical School talked about Thoracic lymphangiomatosis. mTOR inhibitors were tested on patients with a good partial response (Ricci et al., 2015), however, there is no genetic understanding of how these diseases work. Dr Adams also mentioned the existence of patient registries and the use of Ang-2 as a biomarker.
  • Dr Joseph Parambil from the Cleveland Clinic talked about Hereditary Hemorrhagic Telangiectasia, a genetic disorder with autosomal dominance caused by mutations in ENG, ACURL1 or SMAD4 and related to TGF-b The disease has several pulmonary manifestations.
  • Dr Kristin Highland talked about Sjogren Syndrome, a female predominant chronic systemic autoimmune disease commonly associated with follicular bronchiolitis, interstitial lung disease, pulmonary amyloidosis and pulmonary lymphoma.
  • Dr Timothy Blackwell talked about Familial Interstitial Pneumonia, a highly genetic autosomal dominant disease with incomplete penetrance associated with RTEL1
  • Dr Enid Neptune from Johns Hopkins University presented the Marfan Syndrome (MFS) as a template for dissecting multisystem single gene disorders. Mutations in fibrillin-1, which bears homology to TGF-b binding proteins, are found in MFS patients. MFS patients present spontaneous pneumothorax and there is enhanced TGF-b activation in patients with pulmonary symptoms.
  • Dr JP Clancy gave a talk about Cystic Fibrosis and possible therapies for the disease including the use of cystic fibrosis transmembrane regulator (CFTR) modulators like Ivacaftor, gene transfer and gene/RNA editing.
  • Dr Laurie Carr talked about Difuse Idiophatic Pulmonary Neuroendocrine Cell Hyperplasia (DIPNECH), a disorder of the bronchopulmonary neuroendocrine cells with 195 cases reported so far usually in middle-aged women. The disease is often misdiagnosed as asthma even though it has distinct features such as multiple scattered pulmonary nodes. The current treatment is an Octreotide based therapy – a synthetic analogue of somatostatin, a hormonal peptide.
  • Dr Bruce Trapnell discussed Pulmonary alveolar proteinosis (PAP), a male-prevalent disease associated with disruption of GM-CSF signalling, macrophage function and surfactant structure.
  • Dr Francis McCormack, the conference scientific chair, talked about Pulmonary Alveolar Microlithiasis (PAM), a disease associated with filling of alveolar space with calcium phosphate microliths with 1022 cases reported. PAM is associated with mutations in SLC34A2.
  • The session ended with a presentation by Dr Nishant Gupta about Light-Chain Deposition Disease (LCDD), a very rare disease characterized by deposition of non-fibrillary amorphous material in various tissues that has renal failure as a common symptom. Diffuse cystic lung disease in LCDD can mimic other common diffuse cystic lung diseases such as LAM. Matrix degradation by MMPs may lead to cyst formation in LCDD.
  • In a session named “Cystic Lung Disease”, Dr McCormack gave a presentation about lymphangioleiomyomatosis (LAM) and all the LAM clinical trials including the MILES and TRAIL trials and the MIDAS study.
  • Dr Kotloff presented BHD Syndrome – a summary of this talk can be find on last week’s blog post.
  • Dr Abdellatif Tazi presented Langerhans Cell Histiocytosis (LCH), a rare disease characterized by tissue infiltration with Langerhans-like dendritic cells, usually organized into granulomas. Lung pathology includes focal granulomas. The MAKP pathway is known to be involved in LCH.

The RLDC 2016 Cincinnati was the largest and most comprehensive international rare lung disease meeting, bringing together physician-scientists and patient advocates to discuss rare lung disease research and treatments. Patients and families also gave presentations and were encouraged to learn, inspire, and collaborate.

For more information regarding forthcoming meetings that are relevant to BHD research, please check the Conferences and Events page on

  • McCormack FX, Inoue Y, Moss J, Singer LG, Strange C, Nakata K, Barker AF, Chapman JT, Brantly ML, Stocks JM, Brown KK, Lynch JP 3rd, Goldberg HJ, Young LR, Kinder BW, Downey GP, Sullivan EJ, Colby TV, McKay RT, Cohen MM, Korbee L, Taveira-DaSilva AM, Lee (2011). Efficacy and Safety of Sirolimus in Lymphangioleiomyomatosis New England Journal of Medicine, 365 (3), 271-272 DOI: 10.1056/NEJMc1106358

BHD at the International Rare Lung Diseases Research Conference 2016

The International Rare Lung Diseases Research Conference (RLDC) and LAM symposium were held last week over four days.  They brought together clinicians, scientists, patients and families to Cincinnati to review research developments in rare lung disease and to promote dialogue between the research community and patients. Next week’s blog will focus on the highlights of the entire conference. This week the blog is focused on the BHD syndrome specific talk and poster.

Dr Robert Kotloff from the Cleveland Clinic presented the “BHD Syndrome” talk as part of the Cystic Lung Disease session. Dr Kotloff described the case of a 22-year-old female presenting with spontaneous pneumothorax (SP) after a plane flight. SP was managed with a chest tube. One month after discharge, the patient was readmitted with recurrent pneumothorax and underwent video-assisted thoracoscopic surgery (VATS) and pleurodesis. A lung biopsy showed emphysematous blebs and eosinophilic pleuritis. In addition, the patient reported chronic cough but tests showed normal pulmonary function. The patient was referred to LAM/CLD clinic for second opinion and a CT scan revealed lungs cysts. Dr Kotloff mentioned the importance of family history for diagnosis: “In the era of precision medicine, taking a history still matters” – the patient’s mother had chronic cough and a cousin had a history of spontaneous pneumothorax and nephrectomy for renal cancer. Dr Kotloff had his Dr. House moment: “It’s BHD Syndrome. Get renal MRI and call a derm consult stat.”

Dr Kotloff presented BHD as an autosomal dominant disorder characterized by predisposition to fibrofolliculomas, lung cysts, SP and renal neoplasm and talked about the its original description in 1977, the recognition of non-cutaneous manifestations in 1999 and the clear association of BHD with pulmonary disorders in 2007. A quantitative analysis comparing BHD pulmonary cysts to LAM cysts was presented showing that LAM patients present a much higher number of cysts than BHD patients (~150 vs 28) but these cysts are significantly smaller (~18 vs 33 mm2) and more circular. The distribution of the cysts was also shown to be different with BHD cysts more prevalent in lower lung zones. In addition, unlike LAM, BHD pulmonary lung function is relatively normal. Dr Kotloff then mentioned that lung biopsies are not helpful in BHD patients since they are non-specific and that for the cutaneous manifestations a careful examination by a dermatologist is essential. The speaker also discussed what is known already about the characteristics of BHD renal manifestations, the molecular genetics of BHD and the FLCN-mediated pathways. The last part of the talk focused on BHD diagnostic criteria and management.  Regarding BHD management, the recommendations are: genetic counselling/screening of family members, considering pleurodesis after the first pneumothorax, renal imaging every 2 years starting at age 21 – as CT scanning is impractical for lifetime screening, MRI is preferred. For the management of renal neoplasms, intervention is indicated when tumours reach 3 cm in size, ideally via nephron-sparing partial nephrectomy, with cryoablation and radiofrequency ablation as alternatives for poor surgical candidates. At the moment, and unlike in LAM, no proven therapeutic role for mTOR inhibitors is established.


Dr Nishant Gupta presented the poster titled “Management of spontaneous pneumothorax and safety of air travel in patients with BHD syndrome”. The study consisted of a survey sent to BHD patients with questions addressing patient demographics, clinical manifestations of BHD, management of pneumothoraces and episodes of SP during or within 24h after a flight. This study showed that over 75% of BHD patients who completed the survey (ie a self-selecting sample) will experience at least one SP in their lifetime with an 80% chance of recurrence, however, pleurodesis reduced the chance of recurrence in half. The risk of flight-related SP in BHD patients is 8% per patient and less than 1% per flight. Patients experience a considerable amount of anxiety related to the risk of SP during air travel, partially due to the lack of information provided by caregivers. Over half the patients were given no recommendations regarding the safety of future air travel following SP. These results are similar to those presented by Johannesma et al. (2016) that evaluated the incidence of SP in patients with BHD occurring within 1 month after air travel.  The Johannesma study was discussed in a previous blogand the authors concluded that air travel may increase the risk of developing pneumothorax with 9% of BHD patients developing a SP < 1 month after air traveling with a SP risk of 0.63 % per flight. In both studies, to determine whether the pneumothoraces occurred during or shortly after air travel, imaging before and right after would be required. It is essential that patients are properly advised that the presence of any symptoms during or shortly after air travel might indicate a pneumothorax. Further research is required to draw more conclusive associations.

The conference was a wonderful opportunity to meet clinicians, researchers and patients, and to hear about projects helping rare disease research. It is important that BHD syndrome is represented at relevant conferences with talks, posters and the presence of the BHD Foundation to increase awareness in the medical community about the disease.

  • Toro JR, Pautler SE, Stewart L, Glenn GM, Weinreich M, Toure O, Wei MH, Schmidt LS, Davis L, Zbar B, Choyke P, Steinberg SM, Nguyen DM, & Linehan WM (2007). Lung cysts, spontaneous pneumothorax, and genetic associations in 89 families with Birt-Hogg-Dubé syndrome. American journal of respiratory and critical care medicine, 175 (10), 1044-53 PMID: 17322109

PD-L1 expression associates with non-inactivated VHL ccRCC

The loss of the of the tumor suppressor gene VHL and the subsequent deregulation of VHL/HIF/VEGF signalling are known to play a role in development of clear cell renal cell carcinoma (ccRCC). Renal tumours associated with BHD syndrome are histologically diverse and include a percentage of ccRCC (Pavlovich et al., 2002). Anti-angiogenic therapies targeting the VHL/HIF/VEGF pathway have emerged in past years (Rini et al., 2006) but the development of resistance to these therapeutic agents is leading to the development of a new approach based on targeted immunotherapy against immune checkpoint PD1/PDL1 to restore antitumor immune response. In a new study Kammerer-Jacquet et al. (2016) assessed a large series of 98 cases of ccRCC and correlated PDL1 expression with clinical data follow-up of up to 10 years, expression of VEGF, PAR-3, CAIX and PD-1 and complete VHL status. The authors found PD-L1 expression to be associated with non-inactivated VHL tumors and in particular wild-type VHL ccRCC. These tumors could benefit from therapies inhibiting PD-L1/PD-1.

The authors summarized the 98 patient population characteristics and pathological parameters. Tumors with two alterations of the VHL gene (66.3%) were classed as inactivated (inVHL). Those with one or no alteration (33.7%) were grouped as non-inactivated VHL tumors (niVHL). Within this group, tumors with no alteration (11.2%) were classed as wild-type (wtVHL). PD-L1 expression by immunohistochemistry (IHC) was observed in 70.4% of tumors with different patterns of expression. Tumors with PD-L1 expression were associated with a higher tumor stage and metastasis at diagnosis, higher ISUP grade, sarcomatoid component, overexpression of VEGF and PAR-3 protein and dense TIL PD-1 expression. PD-L1 expression was associated with niVHL ccRCC and, in particular, all wtVHL subgroup tumors expressed PD-L1. Expression of PD-1 and the niVHL gene was significantly associated with PD-L1 expression in a multivariate analysis. Patients with PD-L1 expression had a worse prognosis than patients with no PD-L1 with a lower median specific survival from nephrectomy.

In some cancer cases, it has been shown that PD-L1 expression is driven by oncogenic signalling pathways such as PI3K-AKT and MAPK pathways and is termed innate immune resistance (Atefi et al., 2014; Chen et al., 2016). Alternatively, PD-L1 expression in tumors may be induced via adaptive tumor-specific immune signals (Spranger et al., 2014). PD-L1 expression in ccRCC have been previously associated with metastasis, poor outcome and poor prognostic factors such as VEGF expression (Thompson et al., 2007; Shin et al., 2016). Another study reported PD-L1 expression and fewer VHL gene mutations in ccRCC4 tumors. This subtype of metastatic primary ccRCC was associated with poor prognosis under anti-angiogenic therapy with sunitinib, a targeted tyrosine kinase inhibitor (TKI) (Beuselinck et al. 2015). In the present study, wtVHL ccRCC were particularly associated with PD-L1 expression supporting the mechanism of overexpression of PD-L1 being associated with alternative oncogenic pathways in ccRCC despite HIF degradation due to the presence of an activated VHL protein (niVHL). niVHL tumors could use alternative pathways independent of VHL mechanisms such as the MAPK and PI3K-AKT-mTOR pathways involved in ccRCC oncogenesis (Robb et al., 2007; Huang et al., 2008; Mendoza et al., 2011).

In summary, and for the first time, PD-L1 expression by IHC was found to be associated with niVHL tumors, and in particular with wtVHL ccRCC. These tumors may benefit from immunotherapy inhibiting PDL1/PD-1 to produce long-lasting responses in patients. Other advances in immunotherapy for renal cell carcinoma have been discussed in a previous blog.

  • Kammerer-Jacquet SF, Crouzet L, Brunot A, Dagher J, Pladys A, Edeline J, Laguerre B, Peyronnet B, Mathieu R, Verhoest G, Patard JJ, Lespagnol A, Mosser J, Denis M, Messai Y, Gad-Lapiteau S, Chouaib S, Belaud-Rotureau MA, Bensalah K, & Rioux-Leclercq N (2016). Independent association of PD-L1 expression with non-inactivated VHL clear cell renal cell carcinoma – a finding with therapeutic potential. International journal of cancer PMID: 27623354

Air travel and diving possibly increase risk of pneumothorax in BHD patients

Birt–Hogg–Dubé syndrome is caused by germline mutations in the FLCN gene and characterized by skin fibrofolliculomas, lung cysts, spontaneous pneumothorax (SP) and renal cancer.  Because sudden changes in air pressure can increase the chances of developing a collapsed lung, a concern many BHD patients have is whether it is safe to air travel and scuba dive, or whether this increases the chances of a pneumothorax. In a new study, Johannesma et al. (2016) evaluate the incidence of SP in patients with BHD during or shortly after air travel and diving. The study was conducted by sending a survey to a cohort of BHD patients. The authors assessed SP episodes occurring within 1 month after air travel or diving and concluded that exposure to changes in air pressure associated with flying and diving may increase the risk of developing pneumothorax.

A survey was sent to 190 BHD patients, with diagnosis confirmed by FLCN mutations analysis, to collect information about history of spontaneous pneumothorax, flying and diving history within 1 month before the SP episode and adverse effects during flying and diving (including shortness of breath, chest pain, palpitations, anxiety, fatigue, nausea, dizziness, headache, chills and light-headedness). Medical records were collected and reviewed for radiological evidence of SP.

In total, 158 (83.2 %) patients completed the questionnaire. One or more adverse effects were experienced by 30/145 patients (20.7 %) during flight and in 10/54 patients (18.5 %) during diving. 13/145 BHD patients (9.0 %) developed a SP < 1 month after air traveling. The diagnosis of pneumothorax was confirmed in all patients with chest X-ray, additional thoracic CT was performed in some patients. The authors calculated a pneumothorax risk of 0.63 % per flight. 2/54 (3.7 %) developed a SP < 1 month after diving at depths between 3 and 10 m. A pneumothorax risk of 0.33 % per diving session was calculated. Although these patients did not undergo chest radiographic imaging before air travel or diving session, the authors assume that patients developed a pneumothorax during air travel or ascending in the diving session, as patients had no previous symptoms of pneumothorax.

Due to the lack of studies in this subject, recommendations regarding air travel and diving with pneumothorax are variable. The British Thoracic Society (BTS) guidelines on air travel emphasize that patients with a current closed pneumothorax should avoid air travel, patients may be able to fly 6 weeks after a surgical intervention and resolution but careful medical assessment is required. BTS also recommends that after a pneumothorax, diving should be discouraged permanently unless a prevention strategy has been performed (MacDuff et al., 2010). In-flight pneumothorax seems to be rare in the general population (Sand et al., 2009; Peterson et al., 2013). Between 1969 and 2012 a total of 38 episodes of pneumothorax during air travel are described (summarized in Hu et al., 2014), a number of these episodes had LAM as an underlying disease. So far, little data concerning BHD and air travel is available. The same group conducting this new study had previously found that 6.3 % of a BHD patient cohort suffered episodes of pneumothorax within one month of flying (Postmus et al., 2014). Interestingly, although the authors reported no link between air travel and risk of pneumothorax, another study found a similar proportion of BHD patients reported chest tightness following air travel but without being diagnosed with pneumothorax (Hoshika et al., 2012), however the length of the pneumothorax free period after flying was not specified.

The size of the connection between airway and pleural cavity in the lungs is likely to determine how fast a pneumothorax will increase, the location of the cysts in the periphery of the lungs and the lack of a direct connection with the airways supports this theory. Therefore, it may take weeks before a pneumothorax causes symptoms so to determine whether a pneumothorax occurred during or shortly after air travel or diving, imaging before and right after would be required. It would also be interesting to try to correlate specific FLCN mutations with increased risk of pneumothorax.

In summary, the data in this study suggests that patients with BHD might possibly have an increased risk for pneumothorax in flying and diving. Patients with BHD should be advised that the presence of any clinical symptoms during or shortly after air travel or diving might indicate a pneumothorax. Further research is required to draw more conclusive associations and to address the exact rate of pneumothorax during and directly after air travel and diving.

  • Johannesma, P., van de Beek, I., van der Wel, J., Paul, M., Houweling, A., Jonker, M., van Waesberghe, J., Reinhard, R., Starink, T., van Moorselaar, R., Menko, F., & Postmus, P. (2016). Risk of spontaneous pneumothorax due to air travel and diving in patients with Birt–Hogg–Dubé syndrome SpringerPlus, 5 (1) DOI: 10.1186/s40064-016-3009-4

C9orf72-SMCR8 complex, analogous to FLCN- FNIP, localizes to lysosomes and regulates mTORC1

The DENN protein module contains a longin domain, a DENN domain and a d-DENN domain.  Nookala et al. (2012) identified a DENN module in folliculin (FLCN), the Birt-Hogg-Dube tumour suppressor.  The DENN module is believed to be a GEF for Rab-GTPases, although FLCN is believed to act as a GAP for RagC (Tsun et al., 2013) as is its yeast homologue, LST7, in interaction with the yeast FNIP homologue Lst4 (Pacitto et al., 2015).  A recent bioinformatic study identified DENN domains in several other proteins, including Folliculin Interacting Proteins (FNIP1/2), C9orf72 and SMCR8 (Zhang et al., 2012).  SMCR8 was known to be involved in autophagy and C9orf72 in ALS and FTD (Behrends et al 2010; DeJesus-Hernandez et al., 2011; Renton et al., 2011; Smith et al., 2012). Now, Amick et al. (2016) show, interestingly, how they used genetic strategies to examine C9orf72 functions, interactions and subcellular localization.

The authors found that C9orf72 interacts with SMCR8 and that C9orf72 localizes to lysosomes in an amino acid-dependent way. In the absence of C9orf72, the authors observed impaired mTORC1 signalling responses to amino acid availability. Since FLCN and FNIP1 interact (Baba et al., 2006) it was hypothesised that C9orf72 would also interact with FLCN, FNIP1 or SMCR8. Immunoprecipitation assays showed strong interactions of C9orf72 with SMCR8 but not FLCN or FNIP1. Knockdown of SMCR8 by siRNA lead to reduction in C9orf72 protein levels leading the authors to suggest that interaction with SMCR8 is likely to be crucial for C9orf72 function. Clustering analyses revealed that SMCR8’s evolutionary history is most highly correlated with C9orf72, suggesting that their interaction is functionally significant. Other genes that shared correlated evolutionary history with C9orf72 and SMCR8 were proteins involved in regulating lysosomal protease activity and endosomal membrane traffic.

Knowing that FLCN recruitment to lysosomes is negatively regulated by amino acid availability (Petit et al., 2013), the authors investigated the effect of starvation on C9orf72 localization and observed that C9orf72 was recruited to lysosomes in starved cells. After amino acid re-feeding, C9orf72 was redistributed back into the cytoplasm. Starvation treatment, however, did not affect C9orf72-SMCR8 interaction. While C9orf72 localization to lysosomes was regulated by amino acid availability, direct inhibition of mTOR did not affect C9orf72 localization, suggesting that C9orf72’s recruitment to lysosomes is not a result of mTORC1 inactivation triggered by starvation but may be a more direct response to different amino acid levels.

To study the functions of C9orf72 and SMCR8, C9orf72 KO, SMCR8 KO and C9orf72+SMCR8 double KO cell lines were generated. The smcr8 knockout cell lines showed depleted levels of C9orf72 protein and vice-versa. This mutual dependence of C9orf72 and SMCR8 protein levels further supports the idea that their interaction is functionally important. Lysosomes were enlarged and more clustered in the perinuclear region in C9orf72 KO cells than in wild type or SMCR8 KO cells supporting the idea of the lysosome as site of action for C9orf72. While not showing the same lysosome phenotype, the SMCR8 KO cells were larger than the wild type or C9orf72 KO. Interestingly, C9orf72-SMCR8 double KO cells reversed the lysosome clustering and enlargement of C9orf72 single KO and the increased cell size of the SMCR8 KO. mTORC1, being a regulator of cell size (reviewed in Eltschinger and Loewith, 2015), could also contribute this increased cell size. The authors measured mTORC1 signalling by assessing phosphorylation of ribosomal protein S6. Basal S6 phosphorylation was similar to wild type in C9orf72 KO and C9orf72-SMCR8 double KO but increased in the SMCR8 KO cells. In addition, mTORC1 inhibition eliminated the size difference between control and SMCR8 siRNA transfected cells. mTORC1 recruitment to the lysosome is mediated by Rag GTPase (reviewed in Ferguson 2015). Responsiveness of mTORC1 to amino acid re-feeding was impaired in both the C9orf72 and SMCR8 single KO cells. Although C9orf72 and SMCR8 KO cells show defects in mTORC1 regulation by amino acids, mTOR recruitment to lysosomes still occurs in amino acid re-feeding suggesting that the C9orf72-SMCR8 heterodimer is not required for controlling the Rag GTPase-mediated lysosome recruitment of mTORC1. The authors examined the effects of RagC depletion on mTOR recruitment to lysosomes and found that this recruitment was highly RagC-dependent in all WT and KO cell lines indicating that C9orf72 and SMCR8 contribute to the regulation of mTORC1 signalling by amino acid availability in a Rag-independent manner.

It would be interesting to look at the expression pattern of C9orf72 and SMCR8 in the context of FLCN and FNIP expression: it is unclear if there is any functional redundancy between these DENN-domain containing proteins.  In summary, the authors identified a C9orf72-SMCR8 protein complex that shares with FLCN-FNIP1 the ability to be recruited to lysosomes in an amino acid availability-dependent way. Since the FLCN-FNIP complex acts as a GAP, C9orf72-SMCR8 might also act as a GAP. The findings give insights into the functions of this sub-family of DENN domain containing proteins. In addition, the role of C9orf72 and SMCR8 in the mTORC1 signalling pathway suggests that studying their functions may be important for cancer biology research.

  • Amick J, Roczniak-Ferguson A, & Ferguson SM (2016). C9orf72 binds SMCR8, localizes to lysosomes and regulates mTORC1 signaling. Molecular biology of the cell PMID: 27559131