Frequency of truncating FLCN variants and Birt-Hogg-Dubé-associated phenotypes in a health care system population

ERN GENTURIS clinical practice guidelines for the diagnosis, surveillance and management of people with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHD syndrome) is an autosomal dominant multisystem disorder with variable expression due to pathogenic constitutional variants in the FLCN gene. Patients with BHD syndrome are predisposed to benign cutaneous fibrofolliculomas/trichodischomas, pulmonary cysts with an associated risk of spontaneous pneumothorax, and renal cell carcinoma. A requirement for updated International consensus recommendations for the diagnosis and management of BHD syndrome was identified. Based on a comprehensive literature review and expert consensus within the fields of respiratory medicine, urology, radiology, dermatology, clinical oncology and clinical genetics, updated recommendations for diagnosis, surveillance and management in BHD syndrome were developed. With the widespread availability of FLCN genetic testing, clinical scenarios in which a diagnosis should be considered and criteria for genetic testing were defined. Following a clinical and/or molecular diagnosis of BHD syndrome, a multidisciplinary approach to disease management is required. Regular renal cancer surveillance is recommended in adulthood and life-long, but the evidence base for additional tumour surveillance is limited and further research warranted. Recommendations for the treatment of cutaneous, pulmonary and renal manifestations are provided. Awareness of BHD syndrome needs to be raised and better knowledge of the clinical settings in which the diagnosis should be considered should enable earlier diagnosis. Further details, including areas for future research topics are available at: https://www.genturis.eu/l=eng/Guidelines-and-pathways/Clinical-practice-guidelines.html .

Familial pulmonary cysts: A clue to diagnose Birt-Hogg-Dubé syndrome: A case report and literature review

Birt-Hogg-Dubé syndrome (BHD) is an inherited autosomal dominant condition caused by germline mutations in the FLCN gene, mapped to chromosome 17p11.2. Typical manifestations include pulmonary cysts, spontaneous pneumothorax, fibrofolliculomas, and kidney neoplasms. This report details the case of a 56-year-old female non-smoker diagnosed with multiple pulmonary cysts, presenting with a history of recurrent spontaneous pneumothorax. A computed tomography (CT) scan of her daughter revealed similar pulmonary cysts, raising suspicion of BHD. Further abdominal enhanced CT revealed a left renal tumour and cutaneous fibrofolliculomas on her daughter's neck. Consequently, whole-exome sequencing confirmed an FLCN germline mutation in the patient and three relatives, establishing a diagnosis of BHD. This case highlights the importance of familial pulmonary cysts as a clue for diagnosing BHD, providing crucial insights into comparable clinical presentations.

Hereditary Renal Cancer Syndromes

Familial kidney tumors represent a rare variety of hereditary cancer syndromes, although systematic gene sequencing studies revealed that as many as 5% of renal cell carcinomas (RCCs) are associated with germline pathogenic variants (PVs). Most instances of RCC predisposition are attributed to the loss-of-function mutations in tumor suppressor genes, which drive the malignant progression via somatic inactivation of the remaining allele. These syndromes almost always have extrarenal manifestations, for example, von Hippel-Lindau (VHL) disease, fumarate hydratase tumor predisposition syndrome (FHTPS), Birt-Hogg-Dubé (BHD) syndrome, tuberous sclerosis (TS), etc. In contrast to the above conditions, hereditary papillary renal cell carcinoma syndrome (HPRCC) is caused by activating mutations in the MET oncogene and affects only the kidneys. Recent years have been characterized by remarkable progress in the development of targeted therapies for hereditary RCCs. The HIF2aplha inhibitor belzutifan demonstrated high clinical efficacy towards VHL-associated RCCs. mTOR downregulation provides significant benefits to patients with tuberous sclerosis. MET inhibitors hold promise for the treatment of HPRCC. Systematic gene sequencing studies have the potential to identify novel RCC-predisposing genes, especially when applied to yet unstudied populations.

[Genetic diffuse cystic lung disease in adults]

Multiple cystic lung diseases comprise a wide range of various diseases, some of them of genetic origin. Lymphangioleiomyomatosis (LAM) is a disease occurring almost exclusively in women, sporadically or in association with tuberous sclerosis complex (TSC). Patients with LAM present with lymphatic complications, renal angiomyolipomas and cystic lung disease responsible for spontaneous pneumothoraces and progressive respiratory insufficiency. TSC and LAM have been ascribed to mutations in TSC1 or TSC2 genes. Patients with TSC are variably affected by cutaneous, cognitive and neuropsychiatric manifestations, epilepsy, cerebral and renal tumors, usually of benign nature. Birt-Hogg-Dubé syndrome is caused by mutations in FLCN encoding folliculin. This syndrome includes lung cysts of basal predominance, cutaneous fibrofolliculomas and various renal tumors. The main complications are spontaneous pneumothoraces and renal tumors requiring systematic screening. The mammalian target of rapamycin (mTOR) pathway is involved in the pathophysiology of TSC, sporadic LAM and Birt-Hogg-Dubé syndrome. MTOR inhibitors are used in LAM and in TSC while Birt-Hogg-Dubé syndrome does not progress towards chronic respiratory failure. Future challenges in these often under-recognized diseases include the need to reduce the delay to diagnosis, and to develop potentially curative treatments. In France, physicians can seek help from the network of reference centers for the diagnosis and management of rare pulmonary diseases.

A Novel FLCN Variant in a Suspected Birt-Hogg-Dubè Syndrome Patient

Subjects with pathogenic (PV) and likely pathogenic (LPV) FLCN variants have an increased risk of manifesting benign and malignant disorders that are related to Birt-Hogg-Dubé syndrome (BHDS): an autosomal dominantly inherited disorder whose severity can vary significantly. Renal cell carcinoma (RCC) development in BHD (Birt-Hogg-Dubé) patients has a very high incidence; thus, identifying this rare syndrome at early stages and preventing metastatic spread is crucial. Over the last decade, the advancement of Next Generation Sequencing (NGS) and the implementation of multigene panels for hereditary cancer syndromes (HCS) have led to a subsequent focus on additional genes and variants, including those of uncertain significance (VUS). Here, we describe a novel FLCN variant observed in a subject manifesting disorders that were suspected to be related to BHDS and with a family history of multiple cancers.

Recommendations on scuba diving in Birt-Hogg-Dubé syndrome

INTRODUCTION

Although very uncommon, severe injury and death can occur during scuba diving. One of the main causes of scuba diving fatalities is pulmonary barotrauma due to significant changes in ambient pressure. Pathology of the lung parenchyma, such as cystic lesions, might increase the risk of pulmonary barotrauma.

AREAS COVERED

Birt-Hogg-Dubé syndrome (BHD), caused by pathogenic variants in the FLCN gene, is characterized by skin fibrofolliculomas, an increased risk of renal cell carcinoma, multiple lung cysts and spontaneous pneumothorax. Given the pulmonary involvement, in some countries patients with BHD are generally recommended to avoid scuba diving, although evidence-based guidelines are lacking. We aim to provide recommendations on scuba diving for patients with BHD, based on a survey of literature on pulmonary cysts and pulmonary barotrauma in scuba diving.

EXPERT OPINION

In our opinion, although the absolute risks are likely to be low, caution is warranted. Given the relative paucity of literature and the potential fatal outcome, patients with BHD with a strong desire for scuba diving should be informed of the potential risks in a personal assessment. If available a diving physician should be consulted, and a low radiation dose chest computed tomography (CT)-scan to assess pulmonary lesions could be considered.

Update on classification of oncocytic neoplasms of the kidney

PURPOSE OF REVIEW

This review provides a summary of recent developments in classification of renal oncocytic neoplasms that were incorporated in the fifth edition WHO classification of renal tumors, released in 2022.

RECENT FINDINGS

Besides the distinct entities of renal oncocytoma and chromophobe renal cell carcinoma, the WHO now acknowledges a heterogeneous group of oncocytic tumors of the kidney that can be reported as 'oncocytic renal neoplasms of low malignant potential'. Case series by multiple institutions have revealed recurrent patterns of morphological features, protein marker expression, and genetic alterations within these neoplasms that may permit further subclassification in the future.

SUMMARY

The new classification system provides pathologists with the opportunity to simplify the diagnostic workup and reporting of morphologically equivocal oncocytic neoplasms.

Hydropneumothorax as a Presentation of Birt-Hogg-Dubé Syndrome

Birt-Hogg-Dubé syndrome (BHDS) is a rare genetic disorder characterized by cutaneous, pulmonary, and renal manifestations. We present a unique case in which a combination of multiple chronic illnesses, genetic testing, and significant family history led to a diagnosis of BHDS. A 72-year-old male patient presented to their primary care physician with a persistent cough of four months and was admitted to the emergency department after the discovery of a left hydropneumothorax. The patient's medical history was significant for recurrent spontaneous bilateral pneumothoraces diagnosed over 20 years ago, chronic obstructive pulmonary disease (COPD), and many other systemic illnesses. A combination of the patient's significant past medical and family history led to a diagnosis of BHDS. Genetic testing was also done to confirm the diagnosis. Despite benign skin lesions being the most common finding, they are not always present, as seen in our case, which can result in missed diagnosis. Due to the autosomal dominant nature of BHDS, it is vital to make an accurate diagnosis to allow for proper genetic counseling, as the development of renal cancer is the leading cause of mortality.

Update of penetrance estimates in Birt-Hogg-Dubé syndrome

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare genetic syndrome caused by pathogenic or likely pathogenic germline variants in the FLCN gene. Patients with BHD syndrome have an increased risk of fibrofolliculomas, pulmonary cysts, pneumothorax and renal cell carcinoma. There is debate regarding whether colonic polyps should be added to the criteria. Previous risk estimates have mostly been based on small clinical case series.

METHODS

A comprehensive review was conducted to identify studies that had recruited families carrying pathogenic or likely pathogenic variants in FLCN. Pedigree data were requested from these studies and pooled. Segregation analysis was used to estimate the cumulative risk of each manifestation for carriers of FLCN pathogenic variants.

RESULTS

Our final dataset contained 204 families that were informative for at least one manifestation of BHD (67 families informative for skin manifestations, 63 for lung, 88 for renal carcinoma and 29 for polyps). By age 70 years, male carriers of the FLCN variant have an estimated 19% (95% CI 12% to 31%) risk of renal tumours, 87% (95% CI 80% to 92%) of lung involvement and 87% (95% CI 78% to 93%) of skin lesions, while female carriers had an estimated 21% (95% CI 13% to 32%) risk of renal tumours, 82% (95% CI 73% to 88%) of lung involvement and 78% (95% CI 67% to 85%) of skin lesions. The cumulative risk of colonic polyps by age 70 years old was 21% (95% CI 8% to 45%) for male carriers and 32% (95% CI 16% to 53%) for female carriers.

CONCLUSIONS

These updated penetrance estimates, based on a large number of families, are important for the genetic counselling and clinical management of BHD syndrome.