Who should be referred for genetic testing for inherited kidney cancer syndromes?

It is well known that mutations in certain genes can contribute to the development of kidney cancer. The Cancer Genome Atlas and studies investigating germline mutations in adult cancers identified mutations in 6 – 16% (i.e. 6 – 16  out of 100 people) of kidney cancer cases and there are now 15 genes associated with hereditary kidney cancer syndromes (including folliculin, the gene mutated in Birt-Hogg-Dubé Syndrome, BHD). Therefore, identification of individuals who require genetic risk assessment is important to ensure they receive the most appropriate care. However, clinical guidelines on genetic risk assessment are lacking. Clear guidelines are required to aid clinicians to decide who requires further evaluation, how genetic counselling and testing should be performed, and which genes should be considered. This has particular relevance in the US where differing insurance policies on coverage for genetic testing can result in barriers in to access care. To address this a panel of experts, including Professor Gennady Bratslavsky (the invited speaker at our most recent Meet the Expert event), discussed several questions regarding genetic risk assessment for hereditary kidney cancer to develop consensus clinical guidelines (Please note this paper isn’t open access).

A series of questions were curated by a steering committee and grouped into 5 different categories:

  1. Who should undergo genetic risk assessment?
  2. When should genetic risk assessment be performed?
  3. What testing should be performed?
  4. How should germline risk assessment be conducted?
  5. Testing in cases of isolated extrarenal lesions associated with known syndromes.

The questions were reviewed by the expert panel which included urologists, medical oncologists, genetic counsellors, clinical geneticists, and patient advocates. Uniform consensus was defined as ≥85% agreement.

1. Who should undergo genetic risk assessment?

Uniform consensus on who should undergo genetic risk assessment was reached for the following conditions:

  • Individuals with or without kidney tumours with a personal or family history of classic manifestations associated with hereditary kidney cancer (e.g. spontaneous pneumothorax).
  • Individuals with a 1st degree relative with a documented germline mutation (or 2nd degree relative if 1st degree is not available – see family tree diagram below ).
  • Individuals with kidney cancer who also have a 1st or 2nd degree relative with kidney cancer.
  • Individuals with kidney cancer that shows a specific histology (such as hybrid oncocytoma tumours – common in BHD).
  • Individuals with bilateral or multifocal kidney tumours (also common in BHD).

A consensus could not be agreed regarding a cut-off age for genetic risk assessment (i.e. whether age alone was a sufficient criterion to recommend genetic risk assessment in an individual with a kidney tumour).

2. When should genetic risk assessment be performed?

Uniform consensus on when genetic risk assessment should be performed was reached for the following condition:

  • Individuals with a renal lesion less than 3 cm and a strong suspicion for a hereditary cancer syndrome.

It was also agreed that a skin biopsy is not necessary to guide genetic risk assessment in individuals with a kidney tumour and skin lesions resembling those associated with a hereditary cancer syndrome. Other questions, including whether histologic diagnosis (i.e. confirming the type of kidney cancer) is required before genetic risk assessment was more contentious and the panel did not reach a consensus.

3. What testing should be performed?

A uniform consensus was agreed that multi-gene testing should be considered for individuals with more than 1 risk factor for a hereditary kidney cancer syndrome. It was generally agreed (although a uniform consensus was not reached) that individuals with a suspicion for a particular syndrome with a defined gene should be considered for single gene testing.

4. How should germline risk assessment be conducted?

Uniform consensus on how genetic risk assessment should be conducted was reached for the following conditions:

  • Genetic testing should not be performed without prior genetic counselling.
  • Genetic counselling may be offered by a clinician with expertise in hereditary kidney cancer syndromes.
  • A telehealth consultation with a licensed counsellor is also sufficient before genetic testing.

Some of the panel agreed that a standardised video covering the essentials of pre-test genetic counselling was sufficient, however many were concerned about the lack of opportunity for discussion with a qualified provider.

5. Testing in cases of isolated extrarenal lesions associated with known syndromes

This category covered whether genetic risk assessment should be considered for individuals with no kidney lesions or a family history of kidney cancer but have other manifestations outside of the kidney associated with known hereditary kidney cancer syndromes. It was agreed that genetic testing should be offered in the following cases:

  • A single pheochromocytoma or paraganglioma (adrenal gland tumours).
  • A single endolymphatic sac tumour (a tumour in the ear strongly associated with Von Hippel-Lindau syndrome).
  • Uveal melanoma (cancer of the eye).
  • A single fumarate hydratase-deficient uterine fibroid (associated with hereditary leiomyomatosis and renal cell carcinoma (HLRCC)).

Regarding BHD, a consensus was not reached on individuals with a history of spontaneous pneumothorax or skin fibrofolliculomas.


Genetic testing is an important factor in assuring an individual receives appropriate care and management. For example, in BHD individuals should monitor their kidneys regularly and if the need for surgery arises, preserving as much of the kidney as possible is essential.  It was noted that there are several barriers to initiating genetic testing including a lack of confidence of clinicians to discuss the risks and benefits and interpretation and explanation of genetic testing results. Consensus guidelines on genetic risk assessment may aid clinicians to overcome the barriers of initiating genetic testing. As such, the findings here represent the first consensus guidelines for genetic risk assessment in hereditary kidney cancer. However, it should be noted that all panel members were from North America and therefore these findings may not necessarily be applicable worldwide. Additionally, the statements here are relatively broad given there are no previous consensus statements that can be further refined. Therefore, it is vital that follow up meetings are held to further refine and update these guidelines, particularly where there was a lack of consensus.

At the BHD Foundation, we think this is a really important step towards implementing standardised guidelines for the diagnosis and management of BHD. We are happy to further advise on genetic counselling and testing and to help locate specialists in your area. Please do email us with all your BHD related queries.

What are the Different Types of Kidney Cancer?

A recent study estimated that there were 431,000 new cases of renal cell carcinoma (RCC – kidney cancer) and an estimated 179,000 deaths in 2020 worldwide. In non-metastatic settings (i.e., where the cancer is localised in the kidney and has not spread beyond) more than 90% of patients survive at least 5 years. However, in patients with metastatic RCC (where the cancer has spread to other parts of the body) the outcome is poorer.

RCC can be categorised into 2 main groups – clear cell RCC, which accounts for 75-80% of all cases, and non-clear cell RCC (nccRCC), which can be further subdivided into smaller groups based on the differences in histology, for example cell shape and cellular alterations. Around 5% of nccRCC cases have a genetic disposition and, like in Birt-Hogg-Dubé syndrome (BHD), these tumours are commonly multiple and bilateral and have an earlier age of onset compared to nccRCC not associated with a genetic condition. In general, kidney cancer associated with BHD is normally slow growing and rarely metastasises. This blog post will focus on the features and treatment of nccRCC. However, it does not discuss oncocytoma or hybrid RCC, 2 of the most common types of BHD-associated kidney cancer.

Types of nccRCC

  • Papillary RCC – the most frequent type of nccRCC and 2nd most common type of kidney cancer. Several genetic mutations are associated with papillary nccRCC, but this type is not normally associated with BHD.
  • Chromophobe RCC – the next most frequent type of nccRCC and one of the most common types associated with BHD. Chromophobe RCC is also associated with a number of other rare genetic syndromes including tuberous sclerosis and Cowden syndrome.
  • Other types of nccRCC include collecting duct RCC, MiT family translocation RCC and renal medullary carcinoma. None of these have been previously associated with BHD and are all very rare, aggressive forms with poor prognoses.

Although the treatments for advanced clear cell RCC have significantly evolved, little progress has been made in metastatic nccRCC due to the low incidence rates and the clinical and molecular diversity of this cancer, resulting in limited numbers of therapies available. Over the past decade, researchers have produced the cancer genome atlas, an in-depth molecular understanding of key cancer-causing alterations in different cancers. Importantly, this includes some types of RCC including clear cell, chromophobe and papillary and has revealed specific spectrums of molecular features for each type to improve the therapeutic management.

A recent paper by Marchetti et al., describes the most important signalling pathways involved in different nccRCC subtypes and includes an overview of ongoing/recently published clinical trials involving nccRCC patients (1).

nccRCC signalling pathways

There are 3 main pathways that are important in driving tumourigenesis (cancer formation) in nccRCC.

1. VEGF axis pathway

This pathway is involved in angiogenesis (the formation of new blood vessels). This is an important pathway in driving the growth of tumours which need a good network of blood vessels to provide oxygen and essential nutrients. There are several existing anticancer drugs that target this pathway to slow the growth of tumours.

2. Mesenchymal-Epithelial Transition (MET) pathway

This pathway is associated with tumour growth, metastasis and malignant cell infiltration (spread of the cancer). This pathway is particularly important in papillary RCC in which the MET gene is often mutated. A number of MET-directed inhibitory cancer drugs have been developed and some, such as cabozantinib target both the MET and VEGF pathways.

3. mTOR pathway

We have recently discussed the mTOR pathway and its role in BHD-related kidney cancer. Although there are several mTOR inhibitors available which are used in other clinical settings, they have not shown to be effective in the setting of BHD.


Generally, RCCs are characterised by a dysfunctional immune cell infiltrate leading to immune suppression in the tumour microenvironment allowing growth of the tumour. This makes it targetable by immunotherapy drugs that work against the major proteins that mediate the immune suppressive environment in the tumour microenvironment. These major proteins are called PD-1, PD-L1 and CTLA-4.

Although the use of immunotherapies in clear cell RCC was assessed in 2015, it has only recently been studied in the context of nccRCC and there are now several recently published and ongoing clinical trials (see our clinical trials page for more information on how clinical trials work).

  • The recent KEYNOTE-427 phase II clinical trial looked at the efficacy and safety of the immunotherapy pembrolizumab (a PD-1 inhibitor) as a monotherapy in advanced nccRCC (types papillary, chromophobe and unclassified). The study showed promising clinical activity however the response rates were higher for papillary and unclassified RCC than chromophobe.
  • Another phase II clinical trial tested nivolumab (another PD-1 inhibitor) in combination with cabozantinib in 2 cohorts of patients. The first had papillary, MiT family translocation or unclassified RCC and the second had chromophobe RCC. Like the KEYNOTE-427 trial, this showed promising clinical efficacy in the first cohort but there was no response in the second cohort of chromophobe RCC patients.
  • Several other trials assessing immunotherapies or combination immunotherapies are underway and are showing promising preliminary results.

The International Kidney Cancer Coalition have a very user-friendly clinical trials search tool that gives up-to-date information on current clinical trials.

Various novel strategies for the treatment of nccRCC are also emerging and are under investigation (2). These include combination therapy of the PD-1 inhibitor camrelizumab and cytokine-induced killer cells. These are immune cells that can recognise and specifically kill cancer cells. The field of individualised DNA plasmid cancer vaccines is also progressing and are used to induce an anti-tumour immune response.


nccRCC is very diverse and complex but we are constantly improving our knowledge and understanding of these cancers and therefore increasing the number of therapeutic options. However, there is still lots of research to be done including the identification of biomarkers for the prediction of progression and response to treatment for nccRCC. Recruitment of sufficient numbers of patients to clinical trials for nccRCC is still an issue due to the rarity and diversity of this group of cancers. Innovation in clinical trial design will be key to the success of future clinical trials in this context.

One of the most striking observations from this review was the lack of response to immunotherapies in chromophobe RCC. As this is one of the most common types of kidney cancer in BHD patients, it is particularly important to us as a charity that further work can be performed to understand why this is the case. This knowledge is greatly needed to open up the therapeutic potential of these immunotherapy drugs which made huge advances in the treatment of other cancers.


1.        Marchetti A, Rosellini M, Mollica V, Rizzo A, Tassinari E, Nuvola G, et al. Molecular Sciences The Molecular Characteristics of Non-Clear Cell Renal Cell Carcinoma: What’s the Story Morning Glory? 2021 [cited 2021 Sep 10]; Available from: https://doi.org/10.3390/ijms22126237

2.        M S, F M, G A, V M, A C, A L-B, et al. Designing novel immunocombinations in metastatic renal cell carcinoma. Immunotherapy [Internet]. 2020 Dec 1 [cited 2021 Sep 10];12(17):1257–68. Available from: https://pubmed.ncbi.nlm.nih.gov/32998603/

Are there pathogenic variants of FLCN that do not cause kidney cancer, thus avoiding a requirement for lifelong surveillance?

Guest Blog by Richard Thrift

Birt-Hogg-Dubé Syndrome (BHD) is an inherited autosomal dominant disorder caused by mutations in the folliculin (FLCN) gene. About 200 pathogenic variants in FLCN have been identified to date. The three classic symptoms of BHD are spontaneous pneumothoraces, characteristic skin lesions associated with hair follicles (the most common of which are fibrofolliculomas), and kidney cancer (also known as renal cell carcinoma, RCC). Not all BHD patients have all symptoms. In particular, only about 1 in 3 patients develop RCC. It has been suggested, based on very limited data, that some FLCN variants may not give rise to RCC. If it were possible to identify variants that do not increase the risk of RCC, expensive and uncomfortable imaging (typically CT or MRI every three year) could be avoidable for people with those variants.

Matsumoto et al. undertook an extensive literature search to try to identify pneumothorax only pathogenic variants(POPVs) (1) . They found 158 articles, which described 1059 individuals from 575 families. 194 unique pathogenic FLCN variants were identified, with patient details provided in most reports. Patients were evenly split between East Asia (Japan, South Korea, China and Taiwan) (33.3%), North America (32.7%), and Europe (31.7%). They broke down the data to make several interesting observations.

Of the documented patients, 91.9% were shown to have pulmonary cysts. The prevalence of pneumothorax, characteristic skin lesions, and RCC in BHDS were 50.9%, 47.9%, and 22.5% respectively. The median age at first pneumothorax was 34 years (range 10–78 years). The median age at which skin changes were first noted was 38 years (range 20–65 years). The median age at first diagnosis of RCC was 47 years (range 14–83 years).

In previous reports there appeared to be a higher percentage of pneumothorax and fewer dermatological findings and RCCs among patients from East Asia. The current study bears this out and provides a more detailed overview. The prevalence of pneumothorax in East Asians was 74%, vs 45% in Europe and 35% in North America. It’s not clear whether this might be explained by genetic and physiological or environmental differences, but there does seem to be some sampling bias due to differences in diagnostic pathways. Pneumothorax recurred in 2 out of 3 patients (geographic differences were not mentioned).

It typically took 6 years for patients to be diagnosed with BHD following a pneumothorax, compared with 0 years for diagnoses following RCC or skin changes. Lack of awareness by clinicians can delay life-saving screening for RCC.

Out of 991 patients identified, only one had RCC below age 20 (at 14 years of age), while 14 had a pneumothorax before age 20. This bears on the minimum age at which genetic testing should be performed. Ethical considerations are discussed by Borry et al, (2); generally, testing is discouraged before the age at which diagnosis might influence management of the condition.

Matsumoto et al. discuss some of the unavoidable limitations and potential biases of a study based on a review of the literature. FLCN variants were analyzed according to the type of mutation, because different mutations behave differently. 68% were nonsense and frameshift variants, 16% were intronic variants, 6% were missense variants/in-frame deletions, 7% were large deletions/duplications, and 4% were variants affecting transcription initiation. The class of large deletions is significant because these variants are not readily identified by DNA sequencing. These are identifiable by copy number analysis, a technique that has only become common in recent years. Patients with large deletion variants who were tested more than a few years ago have often been told they were negative for BHD.

Ideally, there would be enough data to pinpoint which variants are associated with RCC and which are not. But BHD is a rare disease, and there simply aren’t enough documented patients. Many variants have only been documented a few times; not enough to say “this variant, although known to have caused pneumothoraces, will never give rise to RCC.” So, in order to get a little traction, we can try to focus on the variants that seem least likely to cause major problems.

For most of these classes of variants, it is thought that the mutation either causes the variant protein to be destabilized and rapidly degraded, or causes much less protein to be made because the mRNA is either rapidly degraded or just not functional. Missense variants, small in-frame deletions, and a small percentage of nonsense / frameshift variants (those near the last exon) are the only ones with much hope of making a normal amount of (possibly only slightly defective) protein. It is assumed that in general, inadequate amounts of protein being made will absolutely prevent normal function of FLCN, while normal amounts of (slightly defective) protein might have selective effects on function, perhaps leading to a milder condition that does not progress to RCC.

Of the 194 pathogenic FLCN variants (after eliminating variants known to be associated with RCC), 76 appeared, given the limited data, to be POPV. The authors looked for differences between POPVs and non-POPVS by assessing variant type, location within the gene, age of patients, and number of patients with that variant. There were no statistical differences in type or distribution. Almost 90% of POPVs were found in only three or fewer individuals; clearly there is a decent chance that for many of these variants, RCCs will be found if more patients are tested. There was a tendency for patients with POPVs to be younger than those with non-POPVs; if these patients are observed for a longer time, RCCs may develop in them.

Given the above, of the 76 apparent POPVs, it seems unlikely that the majority of these variants are only linked to pneumothorax. However, it cannot yet be ruled out that some of these may be genuine POPVs. The ability to follow BHD patients with these variants over time and assess whether they develop further BHD-associated manifestations would be greatly beneficial in furthering our understanding of whether certain variants are linked to particular manifestations.

Based on this conclusion, the authors recommend lifelong monitoring for RCC (by CT or MRI) of all BHD patients, since pneumothorax-only FLCN variants are likely to be rare.


1) Matsumoto K, Lim D, Pharoah PD, Maher ER, Marciniak SJ. A systematic review assessing the existence of pneumothorax-only variants of FLCN. Implications for lifelong surveillance of renal tumours. Eur J Hum Genet (2021). https://doi.org/10.1038/s41431-021-00921-x Online ahead of print. 2) Borry P, Evers-Kiebooms G, Cornel M, et al. Genetic testing in asymptomatic minors. Eur J Hum Genet 17, 711–719 (2009). https://doi.org/10.1038/ejhg.2009.25

2) Borry P, Evers-Kiebooms G, Cornel M, et al. Genetic testing in asymptomatic minors. Eur J Hum Genet 17, 711–719 (2009). https://doi.org/10.1038/ejhg.2009.25

Exploring a molecular link between Birt-Hogg-Dubé Syndrome and Tuberous Sclerosis.

Tuberous Sclerosis (TSC) is an autosomal disorder caused by mutations in the genes TSC1 or TSC2. It is characterised by the development of tumours that affect several organs including the brain, heart, kidney, lung and skin. Most TSC-associated tumours are benign however malignant tumours do occur, particularly in the kidneys. As such, TSC and Birt-Hogg-Dubé Syndrome (BHD) share some similar features as well as manifestations that are unique to each condition. Like folliculin (FLCN), which is mutated in BHD, TSC1 and TSC2 also regulate the activity of mTOR signalling. We recently published a blog that reviewed the function of FLCN in regulating mTOR signalling. The authors of the review highlighted work which demonstrated that in kidney tumours derived from BHD patients, the loss of FLCN led to hyperactivation of mTOR. Similarly, in TSC, loss of either TSC1 or TSC2 leads to hyperactivation of mTOR which is believed to be the main driver of tumourigenesis.

A recent paper by Alesi et al., investigated the role that TSC1 and TSC2 play in the regulation of lysosome biogenesis and mTOR signalling (1). Lysosomes are organelles responsible for degradation and recycling of cellular waste. Studying lysosomes is important in this context as they have been increasingly shown to be a driver of tumourigenesis. The activity of mTORC1 (a key player in the mTOR signalling pathway) tightly regulates the transcription factors TFEB and TFE3, master regulators of lysosome gene expression, biogenesis and autophagy. In theory, hyperactivation of mTOR signalling should result in prevention of TFEB translocating to the nucleus where it is active. However, there is conflicting evidence of this in the literature in the context of TSC. This present study shows that despite high mTORC1 activity, the localisation of TFEB is predominantly nuclear. Of interest, this has also been shown for a mouse model of BHD-associated kidney cancer in a paper by Napolitano et al., indicating that TFEB may be a driver of tumourigenesis in both TSC and BHD. This is the opposite of what you would expect and so it is important to understand why this happens.

The authors made use of multiple different models to examine TFEB activity in cells lacking TSC2. In a mouse model of TSC which develops kidney cysts they found a 3-fold increase in the number of lysosomes in the tumours compared to adjacent healthy tissue, indicating an increase in TFEB activity in tumours. They also demonstrated an increase of TFEB with a predominantly nuclear localisation in cells lacking TSC2 in vitro. They confirmed that the nuclear TFEB was active in these cells and that this activity led to an increase in cell proliferation, which is required for tumourigenesis.

As FLCN has been shown to be important for TFEB regulation, Alesi et al., next looked at a combined effect of FLCN and TSC2. They depleted TSC2 and FLCN either alone or in combination in vitro and as expected, saw a significant increase in TFEB nuclear localisation and activity when either TSC2 or FLCN were depleted alone. This effect was further enhanced when both TSC2 and FLCN were depleted. The ability of FLCN to regulate TFEB activity is mediated by the proteins RAGC and RAGD which activate mTORC1. The authors demonstrated an increase in the expression of RAGC and RAGD in TSC2 deficient cells, as well as in FLCN-deficient cells and cells lacking both TSC2 and FLCN. They suggested that this could represent an additional mechanism for sustained mTORC1 activity in TSC2 and/or FLCN-depleted cells. The authors stated that the combined loss of TSC2 and FLCN resulting in an even stronger nuclear localisation and thus activity of TFEB implies that there is a pathogenic link between TSC and BHD and that TFEB may represent a therapeutic target for both these rare conditions.

At the BHD Foundation and Myrovlytis Trust we found this paper exciting. The rarity and complexity of conditions such as BHD and TSC present many research challenges. Identification of common pathways that may be targeted therapeutically against multiple conditions is an extremely attractive approach. Further research needs to be performed to investigate if TFEB can be a therapeutic target for alleviating kidney disease in both TSC and BHD.


1.        Alesi N, Akl EW, Khabibullin D, Liu HJ, Nidhiry AS, Garner ER, et al. TSC2 regulates lysosome biogenesis via a non-canonical RAGC and TFEB-dependent mechanism. Nat Commun. 2021;12(1).

Folliculin: Functions Independent of mTOR and AMPK

Ramirez Reyes et al., recently provided an in-depth review of the functions of folliculin (FLCN). We previously published a blog piece based on this review discussing the role FLCN plays in the mTOR signalling pathway. Following on from this, we now focus on other pathways in which FLCN is involved and discuss the relevance to Birt-Hogg-Dubé Syndrome (BHD).


FLCN has been identified as a negative regulator of ribosomal RNA synthesis and thus loss of FLCN can lead to an increase in translation through increased levels of ribosomes which are required for the hyperproliferative state of cancer cells. FLCN has also been linked to the upregulation of two microRNAs in cystic lesions of primary spontaneous pneumothorax in BHD patients. One of these has been shown to induce apoptosis, and the other is involved in mesenchymal to epithelial transition in lung fibroblasts which may be able to at least partly explain the development of lung lesions found in BHD.

FLCN and EGFR Signalling

A role for FLCN in epidermal growth factor receptor (EGFR) signalling has been demonstrated. Cell growth and mechanisms preventing apoptosis, which are hallmarks of cancer, are examples of events that occur downstream of EGFR signalling. Loss of FLCN in BHD-derived kidney tumours has been shown to enhance EGFR activation and therefore could lead to the hallmarks of cancer described.

FLCN and the Cell Cycle

Loss of FLCN leads to acceleration of progression through the G2/M phase of the cell cycle which results in increased cell proliferation. The mechanism by which FLCN controls this is unknown, but it has been hypothesised that it may be through the regulation of the oncogene cyclin D1. It is well established that activation of mTORC1 leads to an increase in cyclin D1 expression which may contribute to BHD-related tumorigenesis.

FLCN and Autophagy

Autophagy is the process by which cellular molecules are broken down and recycled to provide energy and the building blocks to maintain cellular homeostasis under conditions of stress or starvation. It has been reported that loss of FLCN in cells leads to AMPK-mediated induction of autophagy. This results in an inhibition of apoptosis and increased ATP levels which may confer an energetic advantage in tumours lacking FLCN which would support tumour progression under conditions of stress.

FLCN and Glycogen Metabolism

There is increasing evidence of a key role for glycogen in carcinogenesis and accumulation of glycogen has been observed in many cancer types, including renal tumours from BHD patients. A loss of FLCN has been shown to increase the expression of genes involved in glycogen synthesis. Breakdown of glycogen is also a driver of cancer cell proliferation and survival in models of glioblastoma, breast cancer and colon cancer and has shown to be important in the first steps of metastasis.

The role FLCN plays in cells is exceptionally complex and it not yet fully understood. It is complicated further by conflicting evidence in the literature of what FLCN does depending on the model used. Development of better models to study FLCN in the context of BHD would enable a more precise understanding of how a lack of FLCN contributes to the symptoms observed in BHD. This includes models for all the manifestations of BHD (skin, kidney and lung), better platforms for testing drugs on a large scale, inclusion of computational analysis to look at networks rather than single proteins or pathways. Without this deep knowledge of FLCN biology, development of new therapies is extremely difficult, which is why the BHD Foundation and Myrovlytis Trust are committed to funding research to develop these models so that they can be used to inform the development of treatments for BHD.


1.        Reyes JMJR, Cuesta R, Pause A. Folliculin: A Regulator of Transcription Through AMPK and mTOR Signaling Pathways. Front Cell Dev Biol. 2021;

Folliculin: A Regulator of mTOR Signaling

Birt-Hogg-Dubé Syndrome (BHD) is caused by mutations in the gene folliculin (FLCN). If we can fully understand how FLCN functions in the cell, we can start to develop novel therapies which will restore signalling when FLCN is mutated. Although this seems like a simple task, research has shown that FLCN is involved in a lot of different cellular processes and the pathways involved are actually very complex.

We know that FLCN forms a complex with two other proteins, named folliculin interacting protein 1 (FNIP1) and FNIP2 respectively, and many studies have shown that the FLCN/FNIP complex acts to modulate the activity of mechanistic target of rapamycin complex 1 (mTORC1) and AMP-activated protein kinase (AMPK). Ramirez Reyes et al., provide a comprehensive review of the known functions of FLCN (1). This blog post will focus on the role of FLCN in mTORC1 signalling. Future blog posts will focus on FLCN and AMPK signalling, and other roles of FLCN discussed in by the authors.

What is mTOR signalling and why is it important?

mTOR signalling is a master regulator of cell metabolism, growth, proliferation, and survival. In cancer cells, these pathways are manipulated to create a favourable environment for cancer progression. Cellular metabolism needs to be increased in order to promote cellular growth and proliferation, and survival of these cells is critical for the growing tumour. It is therefore no surprise that mTOR signalling is often affected in not just cancer but many other diseases including metabolic syndromes and neurodevelopmental disorders. In fact, hyperactivation of mTORC1 signalling has been found in over 80% of cancers. Targeting this pathway is very attractive for anticancer therapy, as restoration of aberrant mTOR signalling in cancer cells can slow or inhibit tumour development.

What is the role of mTOR in BHD?

The role of mTOR in BHD is controversial and there have been conflicting reports in the literature of the effect of the loss of FLCN on mTOR signalling. In some cell lines which have reduced FLCN, mTOR activation is reduced (i.e. less cell growth and proliferation). However, in BHD-derived kidney tumours, FLCN has been shown to have the opposite effect and lead to hyperactivation of mTOR.

To further understand how hyperactivation of mTOR contributes to cancer progression it is important to look at the downstream factors that are activated by this pathway. Two of these factors are the transcription factors TFEB and TFE3 (transcription factor binding to IGHM enhancer B or 3). TFEB and TFE3 are known to regulate the expression of genes involved in a wide range of cellular processes including lysosome biogenesis and autophagy which are both important in the recycling of cellular components and cancer progression. Activation of TFEB and TFE3, and therefore transcription of target genes, has been demonstrated in several cancers.

It has been shown that FLCN prevents the translocation of TFEB and TFE3 to the nucleus and consequently prevents transcription of target genes. Loss of FLCN therefore leads to constitutive activation of TFEB and TFE3 and transcription of target genes. Moreover, a paper published in 2020 by Napolitano et al., demonstrates that depletion of TFEB in a mouse kidney model of BHD completely rescues the disease phenotype (2).

FLCN is an essential modulator of these metabolic processes, however the conflicting evidence in the literature means there are still many questions to be answered to fully understand the interplay between FLCN and mTOR signalling. Further research into understanding the role FLCN plays in mTOR signalling will increase our knowledge of tumour progression and facilitate the identification of potential novel therapies. In addition to running the BHD Foundation to provide advocacy and support, the Myrovlytis Trust are committed to uncovering the role of FLCN and developing new therapies through funding research and bringing the research community together to tackle these important questions.


1.        Reyes JMJR, Cuesta R, Pause A. Folliculin: A Regulator of Transcription Through AMPK and mTOR Signaling Pathways. Front Cell Dev Biol. 2021;

2.        Napolitano G, Di Malta C, Esposito A, de Araujo MEG, Pece S, Bertalot G, et al. A substrate-specific mTORC1 pathway underlies Birt–Hogg–Dubé syndrome. Nature [Internet]. 2020 Sep 24 [cited 2021 May 18];585(7826):597–602. Available from: https://www.nature.com/articles/s41586-020-2444-0

Findacure Drug Repurposing for Rare Diseases Conference 2021

The team from the Myrovlytis Trust/BHD Foundation attended the drug repurposing for rare diseases conference (14-15th June 2021) organised by findacure. Findacure aim to build a strong, supportive and collaborative rare disease community to transform the lives of people affected by rare diseases. This conference aimed to bring together industry, patient groups, researchers and clinicians and get them thinking about how we can use drug repurposing in the rare disease field.

Of the 7000 recognised rare diseases, only 400 have licensed treatments. Finding new treatments for all these conditions would take 500 years at the current rate of drug development. There is a clear, urgent need for new treatments and drug repurposing is one way to accelerate this.

Day 1 Highlights

Rick Thompson, CEO of findacure highlighted the advantages of drug repurposing:

A series of short talks from Dr Rona Smith (University of Cambridge), Dr John Liddicoat (University of Cambridge) and Professor Indi Banerjee (Manchester University) showcased examples of drug repurposing and what is needed to drive forward a drug repurposing project. It is more common for clinicians and researchers to pursue this type of project as there can be little financial incentive for industry. However, the cost of developing a new treatment should be weighed against the cost of lifetime healthcare for patients.

Two parallel sessions featured 5 minute ‘lightning talks’ from a range of speakers from patients, clinicians and industry. They focused on the importance of advocacy and raising awareness of rare diseases and discussed the challenges of doing this.

In a session hosted by LifeArc, the headline sponsor of the conference, the challenges of creating collaboration between patient groups and industry was highlighted, from initiating a discussion through to intellectual property rights. However, there are clear benefits of involving industry – they often have greater resources than a smaller rare disease charity, with expertise in the regulatory affairs aspect of getting a drug to market. To help navigate collaboration with industry, LifeArc recently published a report entitled “Repurposing medicines: the opportunity and the challenges”.

Day 2 Highlights

The second day of the conference concentrated on drug repurposing in action. Talks from industry featured George Drakakis (CEO of Purposeful) and Kelly Gray (open innovation manager at Astrazeneca); both considered how patient groups and researchers can collaborate with industry to advance drug repurposing projects. Pulse Infoframe led a discussion on the need for quality data and how this can increase interest from industry to form partnerships. Patient data is vital for all stages of drug repurposing, from pre-clinical through to approval. A patient registry, or a large patient dataset with quality data can be invaluable in clinical trials, in which recruiting enough patients can be difficult due to the rarity of the disease.

Medical student Catriona Chaplin gave an overview of her winning essay for the student voice essay competition. She explained that rare diseases aren’t often a focus of medical training, and through spending time with patients of rare diseases learned that this lack of awareness of rare diseases has a significant impact on both a patient’s life and the healthcare treatment they receive. Catriona also highlighted the fact that patients are in fact often the ‘expert’ in their own rare disease and that doctors need to listen and work in partnership with their patients to ensure the best care.

One of the major strengths of the rare disease community is the involvement of and engagement with patients. A highlight of this conference was that rare diseases were spoken about from various perspectives, from industry, scientific and clinical through to patient groups and patients themselves. This really enforced the importance of collaboration and bringing together different groups and resources to drive the identification of new routes to treatment.

Take Home Messages

  1. Collaboration, collaboration, collaboration! Establishing a solid network between different groups from patients, through to researchers and clinicians, industry partners and regulatory agencies is critical to the success of a drug repurposing projects. Patient charities can be the central point of collaboration and work to bring everyone together.
  2. Projects should be patient focused. Patients need to be at the centre of research and their voice needs to be heard throughout the drug repurposing process.
  3. Clinical trial design needs to be innovative. There are additional challenges when conducting clinical trials for a rare disease, and a multiplatform approach is often the best method. This can involve testing the same drug on multiple, related diseases or testing multiple drugs on the same disease.
  4. Patient registries are important in providing quality data for researchers and clinicians, establishing industry partnerships and clinical trial design.
  5. Raising awareness of rare diseases is vital to improve patient’s lives and the treatment they receive. Rare diseases need to be thought of as more than just the physical symptoms and care should be approached holistically.

The Myrovlytis Trust/BHD Foundation team would like to thank Findacure for organising such an engaging and thought-provoking meeting that has had an impact on us and will drive our thought processes as we move forward with various initiatives. We are looking forward to what the future brings for dug repurposing in rare diseases!

COVID-19 and Pneumothorax – an Observational Study

A recent letter in the European Respiratory Journal by Marciniak et al., has provided an update on pneumothorax in COVID-19 (1). The authors analysed data from the International Severe Acute Respiratory and emerging Infections Consortium (ISARIC) WHO Clinical Characterisation Protocol UK (CCP-UK). This encompassed the first and second wave of COVID-19 in the UK and enrolled 131,679 patients over the age of 18 admitted to hospital with COVID-19. Overall, 0.97% had a pneumothorax at some point during their hospital admission, which is in line with their previous estimate of 0.91% (2). The incidence of pneumothorax was not statistically different between the first and second waves, however there was a marked difference in the incidence between groups of patients who received different levels of respiratory support. Of patients requiring no oxygen, 0.16% had a pneumothorax, this increased to 0.56% for patients requiring oxygen support, 0.96% for patients requiring non-invasive respiratory support and 6.1% for patients who required invasive ventilation.

The authors also analysed whether receiving dexamethasone treatment impacted the incidence of pneumothorax, as a small study from Italy had suggested that there was an increased incidence of pneumothorax in patients who had received dexamethasone  (3). Importantly, Marciniak et al., found no association of dexamethasone with increased risk of pneumothorax. There was however an increased risk of pneumothorax for those with ‘chronic pulmonary disease’ (e.g. chronic obstructive pulmonary disease) in non-critical care wards, but this didn’t translate to critical care patients.

The most serious finding from this study was that having a pneumothorax with COVID-19 was associated with a worse prognosis, and an increased mortality rate. However, there are several limitations to the study which the authors discussed. Importantly, it was not known if the pneumothorax occurred after ventilation, or if the pneumothorax resulted in the need for ventilation and so the authors were unable to determine if the incidence of pneumothorax in ventilated patients reflects the severity of the disease or is a result of medical intervention.

The authors state that the risk factors identified for pneumothorax in COVID-19 are smoking, male sex, chronic pulmonary disease and invasive ventilation. They do not discuss people who are already at risk of pneumothorax and what this means for them. At the BHD Foundation, we felt this was an important study to share with the BHD community but we fully understand that this information may cause concern and anxiety. We have therefore contacted the lead author of the paper, Professor Stefan Marciniak to ask him some specific questions about the work and what it means for BHD patients.

As an expert on pneumothorax what have you seen in your clinic during the Covid-19 pandemic?
In my pneumothorax clinic I have over 500 individuals who previously suffered pneumothoraces from a variety of causes including cystic lung diseases. None appears to have suffered a recurrence due to COVID-19, although I don’t know how many contracted the illness. Having a family history of pneumothorax does increase the risk of recurrence (although this is not specific to BHD patients as the numbers are too small to confirm this). Overall, lifetime recurrence risk for pneumothorax is about 45% for all patients, and seems similar for BHD; however, it’s uncommon for a recurrence to be attributable to infection or strenuous activity.

How does BHD compare to other cystic lung diseases in terms of risk of severe Covid-19/worse prognosis?
Most of my patients with BHD have largely normal lung tissue on CT, so I don’t consider them to have “significant underlying lung disease”. I haven’t advised my pneumothorax patients to shield unless they have significant underlying lung disease e.g. at least moderate COPD.

Do BHD patients who have more significant lung manifestations have an increased risk of worse prognosis?
This is a very difficult question because there aren’t longitudinal studies in which patients have been followed for many years with a diagnosis of BHD. Surprisingly, it isn’t clear if cysts (the most common feature of BHD in the lung) change over one’s life. It is relatively uncommon for BHD patients to have very severe cystic lung disease, although I have seen this rarely in older patients, so it isn’t possible to give a definitive answer.

Are BHD patients who have had an intervention for pneumothoraces (e.g. pleurodesis) more vulnerable to infection with SARS-CoV-2?

Again, I don’t have data to support or refute this, but I can’t think of a plausible mechanism by which prior surgery would render someone more vulnerable. On the contrary, pleurodesis should make COVID-19 pneumothorax less likely.

Finally, what would your advice be to anyone who may be more vulnerable to infection or worse prognosis upon infection? 

Vaccination is safe and highly effective. I would strongly recommend that anyone at risk of COVID-19 should accept vaccination if offered.  There is much disinformation about vaccines on social media and the internet, so if people are hesitant or worried, they should discuss the pros and cons of vaccination with their doctor or read the NHS information pages: https://www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/coronavirus-vaccine/

We thank Stefan for his time in answering our questions and hope that this reassures the BHD community.  If you do have any further questions regarding this study then please email us at contact@bhdsyndrome.org. Additionally, Stefan will be discussing BHD and pneumothorax in our next

Meet the Experts session which is happening this Wednesday 23rd June. You can sign up for the event here, and a recording of the session will be posted on our website afterwards.

1.          Marciniak SJ, Farrell J, Rostron A, Smith I, Openshaw PJM, Baillie JK, et al. COVID-19 Pneumothorax in the United Kingdom: a prospective observational study using the ISARIC WHO clinical characterisation protocol. Eur Respir J [Internet]. 2021 Jun 3 [cited 2021 Jun 17];2100929. Available from: http://erj.ersjournals.com/lookup/doi/10.1183/13993003.00929-2021
2.          Martinelli AW, Ingle T, Newman J, Nadeem I, Jackson K, Lane ND, et al. COVID-19 and pneumothorax: A multicentre retrospective case series. Eur Respir J [Internet]. 2020 Sep 9 [cited 2021 Jun 17];56(5). Available from: https://doi.org/10.1183/13993003.02697-2020
3.          Palumbo D, Campochiaro C, Belletti A, Marinosci A, Dagna L, Zangrillo A, et al. Pneumothorax/pneumomediastinum in non-intubated COVID-19 patients: Differences between first and second Italian pandemic wave [Internet]. Vol. 88, European Journal of Internal Medicine. Elsevier B.V.; 2021 [cited 2021 Jun 17]. p. 144–6. Available from: https://doi.org/10.1016/j.ejim.2021.03.018

Diagnosing BHD in the Lung

This month’s blog posts are focusing on Birt-Hogg-Dubé Syndrome (BHD) and the lung, in line with our Meet the Expert session happening later this month (see here for more details and to sign up for the event). Here, we present 2 recent studies focusing on diagnosing BHD from CT imaging of the lungs, and 1 case report of a woman presenting with a symptom not normally associated with BHD.

1: CT Findings of Pulmonary Cysts
Arango-Díaz et al.,(1) reviewed the CT imaging findings of diffuse cystic lung diseases (DCLD) to provide a practical approach for the evaluation of lung cysts. DCLD are a heterogeneous group of disorders, including BHD, that can be diagnosed based on CT. However, recognising the specific underlying cause of cysts can be challenging as many of these diseases have similar features. CT imaging enables definition of the cysts, including their relationship with the bronchovascular structure and distribution of the cysts within the lung which can be informative for diagnosis. The most common diagnoses are lymphangioleiomyomatosis (LAM) and Langerhans cell histiocytosis (LCH). BHD, Lymphocytic interstitial pneumonia (LIP), and the fungal pathogen Pneumocystis jiroveci can also be the cause of lung cysts and are described in this review. Arango-Díaz et al., summarise the main CT findings of lung cysts and identify features, or combination of features, that are unique to each disorder. They state the importance of taking into account the whole picture to get a true diagnosis, including other physical symptoms (e.g. the fibrofolliculomas and renal tumours associated with BHD), other factors (e.g. smoking, a major cause of LCH), and the distribution of the cysts within the lung. This is particularly crucial to the diagnosis of BHD, as the size and wall thickness of the cyst alone is not sufficient for diagnosis. Cysts in patients with BHD are found to affect the basal and paramediastinal regions of both lungs, a feature that is unique within DCLD.

2: Quantitative Analysis of Cystic Lung Diseases by Use of Paired Inspiratory and Expiratory CT
As discussed above, differential diagnosis of the underlying cause of cystic lung diseases can be done based on CT imaging alone, however, this can be very challenging when the number of cysts is relatively small. Furthermore, early diagnosis of the correct disorder is critical for ensuring that appropriate care is given on time.  The authors proposed to evaluate the ‘dynamic properties’ of cysts during respiration as another diagnostic tool and have devised an index called the cyst-airway communicating index (CACI)(2). The CACI takes into consideration the total lung volume (TLV) and the low-attenuation area volume (LAAV, areas that appear less intense on CT which are assumed cysts) at both inspiration and expiration. 71 patients (15 with BHD, 43 with LAM, and 13 ‘other’) were examined. No difference in the TLV was observed between the different groups, however the difference in LAAV between inspiration and expiration was statistically smaller for BHD compared to LAM or the other group. The CACI was also statistically smaller for BHD compared to LAM/other suggesting there is less communication between the cysts and the airway in BHD. There are limitations to this study which the authors discussed, including the small study size, particularly for the BHD and other groups, and the lack of pathological confirmation that the LAAV truly represented cysts, a major caveat of the study. The CACI may also not be applicable to patients with a large number of cysts, however it does appear to be a useful tool for differentiating BHD from other cystic lung diseases with mild pulmonary symptoms.

3: Birt-Hogg-Dubé Syndrome presenting with chronic progressive dyspnea
This case report describes a 42-year-old female with no history of smoking and a past medical history of asthma, sleep obstructive apnea, and gastroesophageal reflux disease(3). She reported wheezing and dyspnea (shortness of breath) and CT revealed DCLD for which a presumptive diagnosis of bullous emphysema was given. However, her age and lack of smoking prompted further investigation. A physical exam revealed numerous skin-coloured bumps on the face and neck which were later confirmed to be fibrofolliculomas. High-resolution CT imaging of the lungs showed many cysts predominantly in the lower lung. Upon genetic testing, a truncation mutation of folliculin was discovered and a diagnosis of BHD was given. Despite an optimised treatment regime for asthma, the patient continued to experience dyspnea and as such a decision to start continuous positive airway pressure (CPAP) was made.

In the context of BHD, this can be a difficult decision as there is a slightly increased risk of pneumothorax with CPAP treatment, however the benefits outweighed the risks in this circumstance and the patient was given detailed precautions regarding the symptoms of pneumothorax. There are currently no guidelines on the risk of pneumothorax with CPAP therapy in BHD and further research is required to address this issue. The authors also state the importance of considering BHD as a differential diagnosis for DCLD as BHD is not normally associated with significant pulmonary dysfunction, however the early diagnosis of BHD is very beneficial for the screening and early detection of renal tumours.


1. Arango-Dí­az A, Martí­nez-de-Alegrí­a-Alonso A, Baleato-González S, García-Figueiras R, Ecenarro-Montiel A, Trujillo-Ariza M V., et al. CT findings of pulmonary cysts. Clinical Radiology. 2021
This paper isn’t freely available but please contact us if you have any questions.
2. Suzuki K, Seyama K, Ebana H, Kumasaka T, Kuwatsuru R. Quantitative Analysis of Cystic Lung Diseases by Use of Paired Inspiratory and Expiratory CT: Estimation of the Extent of Cyst-Airway Communication and Evaluation of Diagnostic Utility. Radiol Cardiothorac Imaging. 2020
Full paper here
3. Reilly D, Pourzand L, Chima-Melton C. Birt-Hogg-Dubé Syndrome presenting with chronic progressive dyspnea. Respir Med Case Reports. 2021
Full paper here