The first study of Birt-Hogg-Dubé Syndrome (BHD) in China was published in 2008. However, by the end of 2021 there were still only 221 Chinese patients reported in the literature. Given the large population of China, it is very likely that BHD is highly underdiagnosed. In 2019, a Rare Lung Disease Clinic was set up at The First Affiliated Hospital of USCT in Anhui province, China. The aim of the clinic was to improve the diagnosis and management of patients with rare lung diseases including BHD.
This recent study highlights the clinical and genetic features of 50 people from 31 families diagnosed with BHD from January 2017 to December 2021. The average age at diagnosis was 47.4 years (ranging from 18 to 76 years of age). The clinical features of these patients were as follows (please note that not every individual underwent every scan or examination):
- 48 out of 49 people had lung cysts.
- 27 out of 50 people had at least one collapsed lung.
- 29 out of 50 people reported a family history of collapsed lungs.
- 32 out of 47 people had skin symptoms defined as multiple, skin-coloured papules.
- 2 out of 41 people had kidney cancer.
- 4 out of 41 people had a type of non-cancerous kidney tumour called angiomyolipoma.
Focusing on the lung symptoms in more detail, it was reported that the average number of collapsed lungs a person had was 2. The maximum number an individual had was 7. There were 3 episodes of lung collapses on both lungs at the same time (bilateral). Lung cysts were the most common sign. Most people had more than 20 cysts in both lungs which ranged between 1 and 5 cm and were irregular in shape. In all cases, the cysts were found towards the bottom of the lungs, a typical feature of BHD.
Of interest, this is one of the few reports from East Asia which reports a high number of people with skin symptoms. However, only 9 people underwent a biopsy to confirm the type of skin manifestation. 2 were reported to be fibrofolliculomas. 1 was confirmed as a trichodiscoma and the others were confirmed to be epidermoid cysts. The authors of the study discussed the differences seen in their study compared with other studies. They suggested that the skin symptoms may have been overlooked previously. Evidence shows these are increasing reported in newer studies.
The authors also note the low incidence of kidney cancer in this group. They comment that this may be due to selection bias since nearly everyone in the study was recruited through the rare lung disease clinic and not a kidney clinic. However, they also do not exclude the role genetics may play. The low incidence of kidney cancer in East Asian BHD patients has been reported before.
45 individuals underwent genetic testing for BHD (the rest were diagnosed clinically). Of these 45 people, a mutation in folliculin (FLCN) was found in 44. The most common mutations were c.1285dup, c.1285del, which are generally the most reported FLCN mutations. Find out more about understanding genetic mutations here.
Management of BHD
The authors compared the recurrence rate of collapsed lungs between those who had surgery and those who had a more conservative treatment (e.g. a chest drain). Reoccurrence was more common in people who had chest drains.
Only 15 patients underwent annual follow-up in the study. The authors discussed that this could also contribute to the low incidence of kidney cancer seen. Ideally, people with BHD should get regular kidney scans so that any kidney cancer can be found and treated quickly.
This study represents, so far, the largest cohort of individuals with BHD in the Chinese population. Although lung symptoms were still the most reported, there was a high number of individuals with skin symptoms. The Rare Lung Disease Clinic is a multidisciplinary team made up of different specialists. These include a radiologist, pathologist, dermatologist, urologist and thoracic surgeon, as well as lung specialists. You can read more about the different types of healthcare professionals here. The authors state their multidisciplinary approach is the best for the diagnosis and management of BHD. They saw an increase in the number of people diagnosed with BHD year on year after establishing the clinic. In the future, the authors would like to extend their study across different centres to be able to recruit a larger number of individuals.
At the BHD Foundation, we were excited by this approach and were encouraged that it has led to an increase in BHD diagnoses over the last 3 years. We look forward to seeing future studies in China and other East Asian countries to improve our understanding of BHD. We hope to establish a worldwide network to enable people with BHD to access the best possible care.
On June 30th, we are celebrating World Pneumothorax Day. We will be raising awareness of the genetic causes of collapsed lungs. We would love for you to join us and help spread the word using our social media toolkit.