A Study of BHD in the Swedish Population 

A study following a large number of Swedish individuals with suspected Birt-Hogg-Dubé syndrome (BHD) was recently published. 278 individuals from 78 families were followed through genetic testing and clinical assessment for BHD between 2007 and 2019. In the study there were 125 men, 153 women and the average age was 50 (ranging from 15 to 97 years of age). Of the 278 individuals, 186 (around 2 in every 3 people) had a mutation in the folliculin (FLCN) gene associated with BHD.

Clinical Assessment

This diagram shows how many of the 186 people with a FLCN variant had each of the symptoms associated with BHD.

186 individuals with a FLCN mutation:
88 had fibrofolliculomas
75 had at least one pneumothorax
49 had lung cysts
30 had a kidney tumour
17 had kidney cysts
55 had no symptoms

The authors of the study noted that the number of people with lung cysts was lower than in other studies. They explained that it may be lower because not everyone had a scan of their lungs. Additionally, not every individual in the study had a scan of their kidneys.

The authors also looked at other cancers and found that 9 in186 individuals had colon cancer and/or pre-cancerous colon tumours.

Of the 30 people that had kidney tumours, it was known what type of tumour they had in 22 cases:

  • 8 were hybrid chromophobe/oncocytoma
  • 5 were chromophobe
  • 4 had clear cell kidney cancer
  • 1 was papillary type 2
  • 1 was a hybrid papillary/oncocytoma
  • 1 was an angiomyolipoma
  • 1 was benign (not cancerous)
  • 1 could not be classified

Genetic Assessment

11 different FLCN variants were identified across the 186 individuals. One FLCN variant, c.779+1G>T, was found in 44 of the 78 families in the study. It was initially thought that these families were unrelated. Further testing showed that these families were in fact distantly related. For help on how to interpret your FLCN variant, read our previous toolkit post here.

One of the questions about BHD is whether the FLCN variant you have can predict which symptoms you get. This variant has been reported before and was associated with a range of symptoms. In this study, there was also a range of symptoms reported from the families with this variant:

  • 37 out of the 44 families studied had skin symptoms
  • 33 out of the 44 families studied had lung symptoms
  • 17 out of 44 of the families studied had kidney tumour(s)
  • 7 out of 44 families studied had colon cancer and/or colon polyps

It is estimated that 1 in 3265 people in the Swedish population carry this variant. This indicates the prevalence of BHD is at least 1 in 3265 in the Swedish population. The high frequency of this variant in the cohort studied suggested that it may in fact be a founder mutation. This is a mutation  in the DNA of people who first settled there and from which the population grew.


This study follows one of the largest cohorts of individuals with BHD. It provides detailed genetic and clinical insights. However, some individuals still had an incomplete medical history. The authors suggested this was due to the lack of clear diagnostic and management guidelines for BHD. This includes the different type of scans you should have and when. Our latest toolkit describes the different scans and when you may have them. Due to the wide variation in the symptoms of BHD seen in different individuals, BHD can prove to be a diagnostic challenge.

The last author of the study, Dr Christos Aravidis (Department of Clinical Genetics, Akademiska Hospital, Uppsala University, Sweden) kindly provided this quote about their work:

Our long term medical follow-up in Sweden, for more than a decade, identified that a unique and specific genetic change constitutes hereditary predisposition for BHD. This implies that BHD may be underdiagnosed due to the syndrome´s diversity. Physicians should be cautious regarding BHD since an early establishment may help to identify people in cancer risk through imaging techniques.

The authors state there is a clear need for up-to-date diagnostic and management guidelines for BHD. The BHD Foundation strongly supports this statement and are actively working towards the development of these guidelines through the BHD Syndrome International Registry (BIRT). We are thrilled that the registry will be launching next week and encourage as many of you to sign up as possible. Sign up to receive updates about the registry, BHD Foundation events and more here.

BHD Toolkit: Explaining the different types of scans

Birt-Hogg-Dubé Syndrome (BHD) is characterised by 3 main manifestations: skin bumps called fibrofolliculomas, lung cysts and collapsed lungs and kidney cancer. Currently, there is no cure. Therefore, management of your symptoms through regular scans is important to minimise the risk of kidney cancer. However, you may also have scans for your lungs to check for lung cysts or if your lung collapses (called a pneumothorax).

In this toolkit, we will explain the different types of scans you may have and when and why you would have a particular type of scan. The information in this toolkit is meant to provide a general overview of the different types of scans but is not a substitute for medical advice. Please discuss any concerns with your doctor.


These scans are quick and painless and use radiation to view structures within the body. The radiation passes through soft structures and is absorbed by harder structures (e.g. bones). The radiation passed through the body is measured by a detector and creates the final image. It is particularly good at visualising harder structures such as bone, but the images are not very detailed. 

X-rays involve small doses of radiation equivalent to anywhere between a few days and few years of normal background radiation. During the procedure, the body part being scanned will be positioned against the radiation detector with the X-ray machine opposite. The scan will only take a couple of minutes and if done as an outpatient (i.e. not staying in hospital) you can usually go home immediately.  

When would you have an X-ray?

You may have an X-ray of your chest to check if you have a collapsed lung (pneumothorax). This is the most common scan to diagnose a pneumothorax, Imaging such a CT scan (see below) may then be used to investigate further.

CT scan

Also known as a CAT scan, these scans involve multiple x-rays from different angles to create very detailed images of the inside of the body. They are used to diagnose, monitor, and guide treatment in several different conditions. 

CT scans involve radiation equivalent to anywhere between a few days and few years of normal background radiation. During the scan you will be lying on a bed and moved through the scanner which looks like a giant donut (you will never be completely enclosed by the scanner and always be able to speak to someone). The scan normally lasts between 10-20 minutes depending on the part of the body being scanned. Sometimes, to get an even clearer picture of what is going on you will be given a dye (known as contrast). Depending on the reason for the scan the dye can be given as a drink, injected into a blood vessel or given as an enema (capsule put into the bottom).  If you have a CT scan as an outpatient, you can usually go home immediately after but may be asked to wait for 30 minutes to an hour if you have had the dye as in rare cases (1 in 1000 people) it can cause an allergic reaction. 

When would you have a CT scan?

Experts recommend that BHD patients should have a high-resolution CT scan when they are first diagnosed, to show how many cysts are present. There is no need for follow up scans if a patient has no further issues with their lungs. You may also have a CT scan if you have a collapsed lung or potentially to monitor your kidneys. However, getting CT scans regularly is not recommended due to the high doses of radiation.

MRI scan

An MRI scan is a safe painless procedure which uses magnetic fields and radio waves to create images of the body (no radiation). Like CT scans, the images produced are very detailed, however MRI scans are particularly good at visualising softer structures (e.g. the kidneys) in the body. The images can help to diagnose, monitor and manage a condition. 

During an MRI scan you will be put on a bed and moved into the scanner either feet or head first depending on the scan. For an MRI scan of your abdomen, you normally enter the scanner feet first. The scanner is a long tube, some people do find them claustrophobic, but you will always be able to communicate with someone while inside. They also are very noisy, and you will be given earbuds or headphones to wear. In most cases, you can choose to listen to your own music. If you have concerns about this, always talk to your medical team as sometimes they can provide a light sedative. MRI scans range in length depending on the area being scanned and usually last between 20 minutes to an hour. Sometimes, to get an even clearer picture of what is going on you will be given a dye (known as contrast). The dye can be given as a drink, injected into a blood vessel or given as an enema (capsule put into the bottom). If you have an MRI scan as an outpatient, you can usually go home immediately after but may be asked to wait for 30 minutes to an hour if you have had the dye as in rare cases it can cause an allergic reaction.

When would you have an MRI scan?

If an MRI scan is available through your healthcare system, it is the recommended choice of scan to monitor your kidneys. How often you get these scans may vary depending on where you live and/or the size of any kidney tumours. In some countries you may get kidney scans yearly and in other it may be every 2 or 3 years. If you currently don’t have any kidney tumours, you may get scans less often than someone who has kidney tumours.


An ultrasound is a quick, painless scan which uses sound waves to visualise structures in the body. It is the scan used on pregnant women to have a look at an unborn child. Although the images created from ultrasound are not very detailed, they are useful to visualise organs in real time and as it involves no radiation they are completely safe. They usually take between 15-25 minutes. 

When would you have an ultrasound?

If an MRI scan to monitor your kidney isn’t available, you may have an ultrasound. However, ultrasounds aren’t sensitive enough to detect very small tumours.

PET Scan

A PET scan is a painless procedure used to visualise activity in your body rather than just creating images of the structures present. It is often used to investigate and monitor confirmed cases of cancer. The scan involves being injected with a substance which emits radiation (this is known as radiotracer). This substance acts similarly to glucose, the molecule that provides us with energy, and will build up in areas which use a lot of energy. Cancer cells need a lot of energy and therefore the radiotracer accumulates where the active cancer is and is interpreted by the PET scanner as an image. The resulting image shows up areas where the radiotracer is. 

When would you have a PET scan?

It is unlikely you will ever have a PET scan, unless you have kidney cancer that has spread to other organs (metastasised). Kidney cancer associated with BHD is normally slow growing and rarely spreads. Early diagnosis and regular kidney scans will also allow any kidney cancer to be caught early.

Although the symptoms of BHD aren’t normally life threatening, management of the condition is critical to identify and treat any kidney cancer as early as possible. Currently, there are no standardised guidelines for the management of BHD. We know that it can be confusing as different people are told different things depending on your location and healthcare system and individual circumstances. Not only can the type of scan differ, but how often you get a scan can vary.

The BHD Syndrome International Registry (BIRT) is launching in March and aims to collect data on the different types and frequency of scans people with BHD have. This information will hopefully be used to create standardised management guidelines to eliminate any confusion over how to manage the symptoms of BHD. Find out more about the registry here. The BHD Foundation is also happy to answer any questions by email about BHD or help you find a doctor in your area.

New BHD Awareness Leaflet for Doctors

It takes on average 4 years for a rare disease patient to reach a diagnosis and the BHD community is no different. Nearly every person we talk to describes the challenges of being diagnosed with BHD and how many doctors have never heard of it.

To raise awareness of BHD among doctors we have created a leaflet dedicated to the symptoms of BHD. We hope that this resource will prompt doctors to consider BHD when investigating patients with collapsed lungs, lung cysts, skin bumps and kidney cancer. The leaflet also signposts to genetic test centres so that doctors have the information to correctly refer their patients.

We will be distributing the leaflet at key conferences and events, and you can help too by sharing it with your doctors.  

View the leaflet PDF. The printable version can be found here.

Rare Disease Day 2022

Rare Disease Day is an event that takes place every year on February 28th, or in a leap year on February 29th (the rarest day of the year). It marks a global effort working towards equal access to healthcare, diagnosis and therapies for people living with a rare disease. The theme for this year is “Share your Colours”. We are encouraging everyone to light up their houses to raise awareness of rare conditions including Birt-Hogg-Dubé Syndrome (BHD). Information on how to do this can be found below.

There are around 300 million people living with a rare disease worldwide, and over 6000 different rare diseases. Although the stories of those living with a rare disease are unique, they share many challenges. As there are so many different rare diseases, there is often a lack of knowledge and quality information. This means healthcare professionals may not have heard of the condition resulting in difficulties diagnosing, managing and supporting those with rare disorders. There is an urgent need for this to change.   

The BHD Foundation works to raise awareness of the rare genetic condition BHD. BHD has 3 main symptoms: skin bumps (called fibrofolliculomas), lung cysts and collapsed lungs (pneumothorax) and kidney cancer. Each person with BHD may have different symptoms and there is currently no way of knowing which symptoms a person  will get. Roughly 9 in 10 people will get skin bumps, 1 in 4 people will experience a collapsed lung and 1 in 3 people will get kidney cancer.

Early diagnosis of BHD is essential so that the condition can be managed appropriately. This includes regular monitoring of the kidneys to minimise the risk of kidney cancer. The BHD Foundation is excited to be launching a new leaflet aimed at health professionals next week. The leaflet is designed to help doctors recognise the symptoms of BHD and whom to refer patients to if they suspect it. This leaflet will be distributed at skin, lung, kidney and imaging conferences. We hope this resource will raise the profile of BHD among the doctors who are most likely to see BHD symptoms and will lead to earlier diagnosis.

Rare Disease Day Events

We are thrilled to be taking part in Rare Disease Day this year, and invite the BHD community to get involved in the following:

  • Share our social media posts to raise awareness of BHD.
  • Light up your house with the rare disease day colours using your laptop. Information on how to do this is available here. Don’t forget to share it on social media and tag us @BHD_Foundation on Twitter or @birthoggdube on Facebook. We will be lighting up our homes too!
  • Explore the Rare Disease resources which includes a school and equity toolkit.
  • Find events near you with the Rare Disease Day event finder.

We will also be attending Rare Disease Day at the NIH. This is a free virtual event which aims to raise awareness and discuss research into rare diseases. Keep an eye out for our report!

Finally, to raise awareness of BHD and show anything is possible we created a short film with wife, mother, retired engineer, and biologist Lea Nadler about her own BHD journey. She discusses the challenges of getting diagnosed, lung surgery and her experience taking part in an Ironman.

We are delighted to be publishing this with digital health and patient advocate group Congenica. You can watch Lea’s inspirational story here

We hope you join with us and celebrate Rare Disease Day this Monday, February 28th. The BHD Foundation continues to provide support and advice for the BHD community. If you have a question about BHD or would like help finding a doctor in your area, please get in touch by email.  

The BHD International Registry (BIRT) – a first step to unravelling the intricacies of BHD

We are delighted to announce that we will be launching the BHD International Registry (BIRT) in March, and hope that as many of the BHD community as possible can join us to help drive research forward in the field.

A registry is a large database, containing information provided by patients on their condition. We hope in the initial stages to gather enough information to help inform the management of BHD, as well as provide information to help researchers.

One of the most common queries we receive at the BHD Foundation is whether other cancers are linked with BHD. There have been suggestions that this may be the case, but conclusive findings haven’t been made. This is largely because studies have been small – as a rare disease it is hard for clinicians to have enough patients to conduct large scale studies. We are hoping the new registry will overcome these obstacles and that research will benefit from this larger-scale approach.

This is a truly collaborative project. We are very grateful to our working group (clinicians and patients) for their continued help and advice.

To make the BIRT registry a success we need the BHD community to join and enter their data. We launch in March, and will have a dedicated zoom meeting to answer questions and help with any technical issues. It is an exciting time at the BHD Foundation, and we hope you can help to make this a success!

More information can be found here, and don’t forget to sign up for updates to be the first to hear about this and other projects we have planned.

International Day of Women and Girls in Science

Today we celebrate the International Day of Women and Girls in Science. Although there has been a lot of work to engage women and girls in science, they are still under-represented at all career levels. Many barriers have been identified that mean the journey of a woman scientist may not be as easy as for their male counterparts.

Here we highlight just some of the women pioneers of genetics. Their contribution to the field helped build a strong foundation and understanding of genetics. This has further paved the way for research into rare genetic conditions, including BHD. In many cases, the tenacity of these women in the face of discrimination has paved the way for generations of women who are now at the forefront of scientific research. 

Rosalind Franklin (1920 – 1958)

Probably the most well-known female researcher in this list, Rosalind Franklin was a British scientist whose work led to our understanding of the structure of DNA. She used a technique called x-ray crystallography to create photographs that showed the double-helix structure of DNA. This work was used by James Watson and Francis Crick to describe the structure of DNA in a paper in 1953. Despite her work being key to this, Franklin was not acknowledged, and she was unaware her photos had been used. Watson and Crick shared the Nobel prize in 1962 for their work. Franklin died 4 years before this from ovarian cancer, aged 37. Only after her death were her contributions recognised.

Martha Chase (1927 – 2003)

Martha Chase and Alfred Hershey were American geneticists. In a paper published in 1952, they confirmed that DNA was the genetic material of life. Prior to this, there was much debate in the field as to whether genetic material was composed of DNA or of protein. Sadly, Chase was not recognised for her contributions in the same way as her male counterpart. Only Hershey was awarded the Nobel Prize in 1969 for this discovery.

Leena Peltonen-Palotie (1952 – 2010)

Leena Peltonen-Palotie was a Finnish scientist who studied the genetics of disease. Her work helped identify more than 20 genes responsible for a group of inherited genetic conditions known as Finnish Heritage Diseases. She was also an excellent science communicator and appeared on television explaining the importance of her work to the public.

Lihadh Al-Gazali (1950 – )

Lihadh Al-Gazali, born in Iraq, pioneered the study of genetic disorders in Arab countries. She has identified and described several genetic disorders, many of which are rare in the rest of the world. She even has a condition named after her – Al-Gazali syndrome. Al-Gazali also works tirelessly to raise awareness of inherited conditions among Arab countries. She has established clinics and a laboratory to help diagnose genetic disorders and offer genetic counselling.

Mary-Claire King (1946 – )

Mary-Claire King is an American geneticist who discovered that breast cancer could be inherited due to mutations in the gene BRCA1. At the time, most scientists thought that cancer was caused by a virus. Her work on the idea that genetics could cause cancer was fairly novel in the field. In 1976, King was hired to run her own research lab, despite being told she was only hired because she was a woman. Most research labs were run by men, and although there were efforts to hire more women, there was a lot of push-back in the field from those who weren’t used to the idea of women in positions of authority. BRCA1 was identified in 1990, after 17 years of work trying to find a genetic link to breast cancer. A second gene, BRCA2, was identified in 1995, along with the discovery that mutations in these genes also increased the risk of ovarian cancer.

Special Mention: Henrietta Lacks (1920 – 1951)

Although not a scientist, it is arguable that Henrietta Lacks has contributed more to the progression of medical research than any other person. Born in 1920, she died age 31 of an aggressive form of cervical cancer. She was under the care of doctors at the Johns Hopkins Hospital in Baltimore, Maryland, one of the few hospitals that provided treatment to Black people at that time.

While treating her disease, samples of her tumour were taken. Some of the cancerous cells from this sample were passed on to a scientist without Lacks’ knowledge or consent. This scientist, Dr George Gey, found that Lacks’ cells were able to survive and multiply in the laboratory. This was the first time cells could grow outside of a body in a laboratory. Lacks’ cells were in essence, immortal.

The cells, named HeLa (after the first 2 letters in Henrietta Lacks) have been shared widely among scientists around the world. Today, work using her cells has led to key discoveries in many research areas including cancer, immunology and infectious diseases. Now, some scientists have called for a reduction in the use of the HeLa cells, as they were taken unethically without Lacks’ knowledge or consent. However, the Lacks family don’t want this to happen. They want to celebrate her life, honour her legacy and acknowledge her history. They also want to educate future generations on the impact of her cells. Find out more about Henrietta Lacks here.

The Myrovlytis Trust and BHD Foundation are passionate about gender equality in research. We recognise the achievements of the women in this article and so many others that have contributed to advancing our scientific understanding, often in the face of adversity. We understand there is still a long way to go to reach gender equality in science. We strive to support women in science where possible. At our virtual BHD Symposium held in October 2021, nearly half (10 out of 22) of our research talks were given by women. In the patient-focused sessions, 5 out of 8 speakers were women. If you missed our patient-focused sessions, you can watch them here. We are also very excited to be planning a patient-focused symposium later this year. To be the first to know about our plans, sign up to our newsletter here.

A potential new kidney cancer treatment for von Hippel-Lindau disease (VHL) 

An exciting new study has just been published looking at a potential new drug to treat von-Hippel-Lindau (VHL) disease. Here, we describe the study and discuss what this may mean for Birt-Hogg-Dubé Syndrome (BHD), which has similarities with VHL.

VHL is a rare genetic disorder, caused by mutations in the VHL gene. Around 7 in 10 people with VHL develop kidney cancer and need multiple surgeries during their lifetime. A drug that can reduce the size of, or completely remove tumours could prevent the need for surgery. 

The VHL protein regulates the activity of another protein called hypoxia-inducible factor (HIF), which is involved in our response to low oxygen conditions. When oxygen levels are normal, VHL will act to stop the activity of HIF. However, when oxygen levels are low, the HIF protein becomes active. This stimulates the formation of blood vessels to help increase the flow of oxygen into our tissues When VHL is mutated, is loses the ability to control HIF, which is then in a permanently “on” state, even with normal oxygen levels. In VHL kidney cancer, the tumours often have more blood vessels. This is thought to be a result of uncontrolled HIF activity. If a drug were able to stop HIF activity in kidney cancer it would represent an exciting new therapy for patients with VHL.

Jonasch et al., wanted to test this theory using a drug called Belzutifan, which inhibits the activity of HIF. This drug has already shown some effect in clear-cell kidney cancer. In a clinical trial (a controlled way to test if a drug is working in humans), they tested the activity of this drug in VHL patients with kidney cancer.

How did the trial work? 

61 patients with VHL disease entered the trial. Patients were all over 18 years old, with at least one kidney cancer tumour bigger than 1cm. Patients were not allowed to join if they had tumours over 3cm in diameter, as these would require surgery. Patients with cancer which had spread to other areas were not allowed to take part.


Patients were given the drug as a tablet orally once a day. Patients left the study if the drug produced unacceptable side effects, or the cancer continued to progress. The researchers looked at the effect of the drug in each patient after 21.8 months on average.


30 of the 61 patients showed a reduction in the size of their tumours (termed a partial response). Another 30 patients showed no progression of the cancer in this time period (termed stable disease). One patient left the trial before the first measurements were taken. 

Visual representation of the results above.


Side effects are common with all drugs, and all patients experienced at least one side effect. The most common side effects were anaemia (low red blood cell count), fatigue (unusual tiredness not related to activity), headache and dizziness. Only one patient stopped taking the drug due to side effects.


Belzutifan is a potential new drug for the management of VHL kidney cancer. As in BHD, when tumours reach 3 cm in diameter in VHL disease, they are surgically removed. A drug that can reduce the size of, or completely remove any tumours is likely to result in fewer surgeries. On average, the patients in this trial had already had 4 previous surgical procedures. Interestingly, only 3 of the patients in the study needed surgery since it began. These results show the drug worked well in VHL kidney cancer, was safe and the side effects were well tolerated. More work needs to be done to see when the best time to take this drug would be, and how it would benefit patients.

The BHD Foundation are very excited by the results of this trial. Folliculin, the gene mutated in BHD, is also known to activate HIF. It may be possible that belzutifan could have some benefits for individuals with BHD. To find out more, we spoke to one of the researchers involved in the trial and BHD expert Dr Marston Linehan (National Cancer Institute, NIH). 

Why is another approach for kidney cancer management needed for individuals with VHL disease? 

The reason we worked on the development of a treatment for VHL kidney cancer over the past 38 years is so that we would have an alternative to surgery for these patients and could delay or completely prevent kidney tumor development.

What are the next steps for taking belzutifan from clinical trials to approved use in patients with VHL disease? 

We still have many questions to answer such as:

  • When is the optimal time to prescribe the agent for VHL-associated renal tumors?
  • How long is the optimal time period to give the agent in patients with VHL-associated kidney tumors?
  • We need to identify the causes of tumor resistance to therapy.

What can we learn from this trial to look at potential treatments for BHD? 

  • We can learn about the potential for targeted systemic agents in patients with genetically defined, inherited forms of kidney cancer such as BHD.
  • Also, although we worked towards the development of agents targeting the VHL pathway to treat kidney cancer, in the belzutifan trial we learned that this agent also has activity in treating central nervous system tumors (CNS hemangioblastomas) and pancreatic neuroendocrine tumors.
  • As we have worked on the development of a therapeutic approach for the treatment of tumors in patients affected with BHD over the past 25 years, it is our hope that when we see the development of an effective approach to target the FLCN (BHD gene) pathway that we will see effect on not only the BHD-associated kidney tumors, but also on BHD-associated pulmonary cysts and cutaneous fibrofolliculomas.
  • We have a way to go, however, we are encouraged by the progress that has been made.

Do you think this approach is the future for management of BHD?

Yes, I do feel that this is the future for the management of BHD.  This was our goal, our “vision”, when we started on VHL in the early 1980’s.  It was also our goal when we started working on BHD in the mid 1990’s.  We will not stop until we have seen the development of effective forms of treatment for all patients affected with BHD and VHL, as well as those affected with Hereditary Papillary Kidney Cell Carcinoma (starting in 1991), Hereditary Leiomyomatosis and Kidney Cell Carcinoma (HLRCC) (starting in 1989) and TFE3, TFEB and MITF kidney cell carcinoma (starting in 1987).

We are very appreciative of the support and encouragement of the Myrovlytis Trust and of the brave and courageous BHD patients who have made it possible for us to make the progress we have over the past 25 years.  We are optimistic about the future. 

The BHD Foundation are extremely thankful to Dr Marston Linehan for his time and his passion and work on BHD and other hereditary kidney cancers.

Can Benign Tumours in Tuberous Sclerosis Complex be Treated with Immunotherapy?

Tuberous Sclerosis Complex (TSC), is rare genetic disorder that can lead to the growth of non-cancerous (benign) tumours. TSC most commonly affects the brain, skin, lungs, heart, eyes and kidneys. Individuals are also at risk of developing kidney cancer. It is caused by mutations in the genes TSC1 or TSC2. These genes also affect the same pathway that FLCN, the gene mutated in BHD does. We have previously written a blog post about this link. Therefore, research being done in TSC may be of interest and applicable to BHD, and vice versa. In this blog post, we discuss a recent paper investigating the development of an immunotherapy treatment for TSC. Immunotherapy is a type of treatment used in cancer that helps your immune system fight the cancer cells.

Tumours that develop in TSC are a result of the loss of both copies of TSC1 or TSC2. It is possible to identify particular genes or molecules that are only found in tumour cells with a TSC1 or TSC2 mutation. These molecules will not be expressed in “healthy” cells. It may be possible to develop an immunotherapy treatment that can specifically recognise these molecules. This in turn leads to killing of those cancer cells and a reduction in tumour size or even kill the whole tumour itself.

In this paper, Thomas et al., observed overexpression of a molecule called GD3 on the surface of TSC tumour cells. GD3 is normally expressed during brain development but is abnormally expressed in several cancers. GD3 is also known to accelerate tumour growth. They showed that the enhanced expression of GD3 in cells correlated with hyperactivation of mTOR. This suggests that GD3 expression is linked to mTOR activation.

The researchers developed a type of immunotherapy called CAR T cells. As the name suggests, the main component of these are T cells. T cells are a key part of our immune system as they are often the first cells to recognise something is “foreign” in our bodies (e.g. cells infected with a virus). They can then coordinate the immune system to mount a response, or the T cells can directly kill the “foreign” cells instead. The “CAR” in CAR T cells is the bit that enables the T cells to specifically recognise something and kill only those cells. In this instance, the CAR is made to specifically recognise the GD3 molecule and kill the TSC-associated tumour cells.

They tested the GD3 CAR T cells in 2 different mouse models of TSC2-related tumours. In one model, they measured the volume of the tumour over time with GD3 CAR T cell treatment compared to control treatments. They saw that although the tumour volume had increased, the tumours were significantly smaller in those receiving GD3 CAR T cell therapy compared to controls. In the second model, they looked at the number of tumours in the liver and kidney. There was a significant reduction in the number of tumours in the mice that received the GD3 CAR T cell therapy compared to control treatment. They also examined the safety of GD3 CAR T cell therapy in the mice and saw no changes in the tissues they tested.

The work presented in this paper is a promising first step towards treatment for benign tumours in TSC. Although not cancerous, the tumours can cause significant and serious problems. As they can grow anywhere, they can block blood flow or prevent normal functioning of many organs. Developing a treatment for these tumours would therefore be of great benefit. CAR T cells are a very new type of treatment, only approved for certain types of blood cancer. There are currently many clinical trials looking at the safety and effectiveness of CAR T cell therapy in other cancers. It’s a complex procedure and, like many other cancer drugs, can have serious side effects. This approach could have some benefit for the treatment of BHD. However, the tumours associated with BHD are not normally life threatening in the same way as they are in TSC. Regular monitoring of the kidneys minimises the risk of kidney cancer. Tumours are normally removed when they reach 3cm and do not normally affect the function of the kidneys. Therefore, the benefits of this type of treatment must be weighed carefully with the risks. Nevertheless, due to the link with mTOR, it would be interesting to see if GD3 was also upregulated in BHD-associated tumours.

BHD Toolkit: Understanding your Genetic Test Result – Amino Acid Mutations

Our last BHD toolkit provided you with all the information needed to understand and interpret your DNA sequencing result, however it didn’t go into details on how to understand the mutation at the protein level.

On your test result this may look something like p.(Trp511*) or something a little more complicated like p.(His429Profs*27).

Please note that your result may look different depending on the test provider. If there is something on your result you don’t understand, please ask your clinician or genetic counsellor, or contact us for further help.

From DNA to Protein

DNA is a unique code that contains all the instructions required for making the proteins needed for the development, growth and function of our bodies. The building blocks of our DNA are called nucleotides. There are four of these made of the bases: adenine, cytosine, guanine and thymine. The sequence of these determines our unique genetic code and tells the machinery in our cells what proteins to make, through an intermediate molecule called RNA. RNA carries the message of the DNA and allows it to be translated into proteins. It is very similar to DNA, however a base called uracil, replaces the base thymine.  

Image shows the flow of information from DNA to RNA (transcription) and RNA to Protein (translation).

Like DNA and RNA, proteins are also made of building blocks. These are not like those in DNA and RNA and are called amino acids. Our DNA is read in triplets: 3 bases (also called a codon) code for 1 amino acid. There are 20 different amino acids that can be made from the following different combinations:

Image shows which combination of nucleotides produce each amino acid. A key explaining the abbreviations for the amino acids is on the right.

There are also 3 codons that do not code for an amino acid and instead signify for the protein to stop being made.

Interpreting Protein Mutations
Interpreting your protein mutation is very similar to interpreting your DNA mutation – you just need to know how to break it down into pieces!

Firstly the p. at the beginning tells us that this result is at the protein level.

The next three letters refer to the amino acid that is normally there in a non-mutated version of folliculin (see the above image).

The numbers that follow this refer to the position of the amino acid in the sequence.

The next bit(s) tell us what has happened to that particular amino acid at the position, for which there are a few different options

  1. The numbers may be followed by ‘del’, which doesn’t stand for an amino acid and means deletion.
    e.g. p.(Phe157del) – the amino acid phenylalanine at position 157 has been deleted.
  2. It is also possible for there to be a larger deletion.
    e.g. p.(His111_Gln116del) – the amino acids from position 111 through 116 have been deleted.
  3. There may also be another three letters referring to a different amino acid.
    e.g. p.(Glu434Lys) – a Glutamine at position 434 has been swapped to a Lysine.
  4. There also may be no letters after the numbers and there is only an *.
    e.g. p.(Trp511*) – the amino acid tryptophan at position 511 has been mutated to a stop codon and the rest of the protein will not be made.

It also possible that the result will look even more complicated as suggested above such as p.(His429Profs*27). Based on the above information it can be inferred that the amino acid histidine (His) at position 429 has been changed to a proline (Pro). However, the remaining fs*27 is yet to be explained.

The fs stands for frameshift. As our DNA is read in triplets, if a single amino acid is deleted or inserted it knocks the reading of triplets out of frame and means that the triplets are not read as they were designed. This can result in the introduction of a premature stop codon, as is the case with the p.(His429Profs*27). The fs*27 indicates that a frameshift has introduced a stop codon (*) 27 amino acids after the mutation.

FLCN mutation
DNA: c.1285dup
Protein: p.(His429Profs*27)

FLCN Genetic Code: 
An image of the genetic code of folliculin from amino acids 420 to 430, with amino acid 429 (Histidine) highlighted.
Mutated FLCN Genetic Code:
An image of the genetic code of folliculin from amino acids 420 to 430, with amino acid 429 (Proline) highlighted. 
Accompanying text: The  C at nucleotide position 1285 has been duplicated which has resulted in the 429th amino acid changing from a histidine to a proline.
The next image shows the FLCN genetic code from 445 - 455.
Accompanying text: Looking further down the sequence we can see that a stop codon (*) has been introduced at amino acid 455 - 27 amino acids down from the original histidine (inclusive of the histidine itself).

It is also possible that your sequencing result may look like p.? – in which case the change at the protein level is unknown and cannot be predicted. This occurs when the type of DNA mutation is a splice-site mutation. You can read our previous BHD Toolkit post which explains the different types of DNA mutations here.

We hope you enjoy these toolkit posts and find them useful. If there is any aspect of BHD you would like us to do a deep dive on and explain in more detail, please let us know by email.

Winter BHD Case Report Round-Up

This week’s blog post contains a round-up of the latest case reports for Birt-Hogg-Dubé Syndrome (BHD) in the literature.

Case Report 1

Firstly, a case report by Degheili et al., documents BHD in 2 individuals with kidney cysts but no kidney tumours. As opposed to tumours, which are solid masses of unusual tissue, cysts are small sacs normally filled with air or fluid. Kidney cysts do not normally impact the function of the kidney but in rare cases can grow large enough to cause pain or discomfort and can block the flow of urine through the kidneys.

The first case was a 70-year-old woman referred for investigation of cysts on her lungs. The patient also had innumerable pale skin bumps on her face and upper torso which were later confirmed to be fibrofolliculomas. A CT scan of her kidneys revealed bilateral cysts and were considered simple. The patient was followed for four years and both lung and kidney cysts remained stable, with the formation of no new cysts.

The second case was a 50-year-old woman with a personal and family history of recurrent pneumothoraces, as well as several skin lesions characteristic of BHD. Genetic testing of the folliculin gene confirmed the diagnosis of BHD. CT scans revealed cysts on both her lungs and kidneys with no kidney tumours.

It is questioned whether the presence of kidney cysts is an incidental finding, or a true feature of BHD. Renal cysts are found in as many as 4 in 10 people in the general population. However, these tend to be isolated, unilateral and simple, compared with the multiple bilateral cysts found in these patients, and in the reported literature on kidney cysts in BHD. However, without further documentation of kidney cysts on a larger scale, an association cannot yet be made.

Case Report 2

In this case report by Lakhani et al., BHD was diagnosed through incidental findings on a lung CT scan. A 59-year-old male presented to the hospital following a CT scan of the lung, abdomen and kidney as part of a trauma workup which revealed the presence of lung cysts. A second CT scan of the chest showed multiple, thin-walled, cysts with a basal distribution (i.e. cysts were located at the bottom of the lungs). The patient had no personal or family history of spontaneous pneumothoraces or kidney cancer. Despite this, and due to the characteristics of the cysts in the lung, BHD was suspected and was confirmed by genetic testing.

BHD is thought to remain underdiagnosed, partly due to variation in clinical presentation as well as lack of awareness. This case report highlights the importance of spreading awareness of BHD within the medical community, as lung cysts found incidentally on imaging studies may be the first sign of BHD in many cases. Early diagnosis of BHD can be critical in minimising the risk of kidney cancer. The BHD Foundation is creating a BHD awareness leaflet that will be circulated to the doctors who are likely to come across the first signs of BHD including dermatologists (skin doctors), radiologists (doctors who review images) and lung doctors,

Case Report 3

The final case report documents a 37-year-old male who was admitted to hospital with lower back pain and hematuresis (blood in the urine). The patient had a personal and family history of spontaneous pneumothorax. A CT scan of the kidney showed a mass on the right kidney and robotic-assisted surgery was performed to remove the tumour. It was noted that the tumour had an unusual shape, and upon further investigation of a sample of the tumour tissue, the tumour was considered as an unclassified type of renal cell carcinoma (RCC). This is unusual for individuals with BHD who normally present with chromophobe, oncocytoma or a hybrid chromophobe/oncocytoma type of RCC.

Genetic testing was performed and a mutation in the folliculin gene was found. In BHD, mutation of a single copy of folliculin is sufficient to cause the skin and lung manifestations, but it is thought that a mutation in the second copy is required for the development of kidney cancer. In this report, it appears that they did not observe a mutation in the second copy of folliculin in the kidney tumour tissue, however it is unclear whether any other genes known to be drivers of cancer development were analysed for mutations. If there were no other mutations and only a single copy of folliculin was mutated this report would represent a rare finding of kidney cancer in and individual with BHD.

Case reports such as these are invaluable additions to the BHD scientific literature that can raise questions about uncommon manifestations or highlight different routes to diagnosis that can increase our knowledge and understanding of the condition. As well as this, they can also help to raise awareness of BHD among clinicians which is an important aspect of the work of the BHD Foundation.