Delayed diagnosis of Birt-Hogg-Dubé syndrome due to marked intrafamilial clinical variability: a case report

Germline- and Somatic-Inactivating FLCN Variants in Parathyroid Cancer and Atypical Parathyroid Tumors

CONTEXT

Parathyroid cancer (PC) is a rare endocrine neoplasm with high mortality. While surgery is the treatment for patients with the disease, recurrence rates are high, and patients usually succumb to severe hypercalcemia. There is no effective systemic therapy for the disease.

OBJECTIVE

To investigate for novel genes causing parathyroid cancer.

METHODS

We analyzed the germline DNA of 17 patients with "sporadic" PC and 3 with atypical parathyroid tumors (APTs) who did not have germline CDC73 or MEN1 pathogenic variants. Sequencing of available tumor tissue from 14 patients with PC and 2 with APT was also performed (including 2 patients with no available germline DNA). In addition, sporadic parathyroid adenomas from 74 patients were analyzed for FLCN variants.

RESULTS

We identified germline FLCN variants in 3 unrelated patients with PC. The 2 frameshift variants have been described in patients with Birt-Hogg-Dubé (BHD) syndrome, while the pathogenicity of the missense variant c.124G > C (p.G42R) has not been definitively established. Functional analysis of the missense variant showed a potential effect on posttranslational modification. All 3 patients with germline FLCN variants were noted to have renal cysts and 2 had lung cysts, features associated with BHD syndrome. Somatic FLCN variants were identified in tumors from 2 (1 APT) of 16 patients with PC/APT and in none of the 74 sporadic parathyroid adenomas. No second hits in FLCN were noted on sequencing; however, loss of heterozygosity at the locus was demonstrated in 2 of 3 patients with the identified germline FLCN variant.

CONCLUSION

The finding of FLCN variants associated with PC may provide the foundation for the development of therapy for this malignancy.

Bibliometric Analysis of Birt-Hogg-Dubé Syndrome From 2001 to 2021

Background

Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominant inherited disorder caused by germline mutations in folliculin (FLCN). Despite our significantly evolved understanding of BHD over the past decades, no bibliometric analyses have been conducted in this field. This study aimed to analyze and visualize the characteristics of publication outputs, the research hotspots, and scientific frontiers about BHD using bibliometric analysis.

Methods

All relevant literature on BHD was culled from the Web of Science Core Collection (WoSCC) database. Valid data were extracted from the articles and visually analyzed using CiteSpace and VOSviewer.

Results

A total of 751 qualifying papers were included. Publication outputs concerning BHD increased over time. The dominant position of the United States and Japan in BHD research field was evident. National Cancer Institute (the USA) and Yokohama City University (Japan) were the two most productive organizations. W. Marston Linehan exerted a considerable publication impact and had made the most remarkable contributions in the field of BHD. Plos One was the journal with the highest publication outputs, and half of the top 10 journals and co-cited journals belonged to Q1 or Q2. Keyword citation bursts revealed that management, tumor suppressor, flcn gene, spectrum, diagnosis, risk, computed tomography were the emerging research hotspots.

Conclusion

Research on BHD is prosperous. International cooperation between countries and organizations is also expected to deepen and strengthen in the future. Our results indicated that FLCN-associated pathways involved in the pathogenesis of BHD, specific options for early diagnosis, and molecular-targeting therapies will remain research hotspots in the future.

Birt-Hogg-Dubé syndrome

Birt–Hogg–Dubé syndrome (BHD) is a rare inherited autosomal dominant disorder caused by germline mutations in the tumour suppressor gene FLCN, encoding the protein folliculin. Its clinical expression typically includes multiple pulmonary cysts, recurrent spontaneous pneumothoraces, cutaneous fibrofolliculomas and renal tumours of various histological types. BHD has no sex predilection and tends to manifest in the third or fourth decade of life. Multiple bilateral pulmonary cysts are found on chest computed tomography in >80% of patients and more than half experience one or more episodes of pneumothorax. A family history of pneumothorax is an important clue, which suggests the diagnosis of BHD. Unlike other cystic lung diseases such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis, BHD does not lead to progressive loss of lung function and chronic respiratory insufficiency. Renal tumours affect about 30% of patients during their lifetime, and can be multiple and recurrent. The diagnosis of BHD is based on a combination of genetic, clinical and/or skin histopathological criteria. Management mainly consists of early pleurodesis in the case of pneumothorax, periodic renal imaging for tumour detection, and diagnostic work-up in search of BHD in relatives of the index patient.

Birt–Hogg–Dubé syndrome is a rare genetic disorder characterised by multiple lung cysts, recurrent pneumothoraces, skin lesions and kidney tumours. As the presenting symptoms may be respiratory, chest physicians should be able to identify this disease.https://bit.ly/2xsOTuk

Matching clinical and genetic diagnoses in autosomal dominant polycystic kidney disease reveals novel phenocopies and potential candidate genes

Purpose

Autosomal dominant polycystic kidney disease (ADPKD) represents the most common hereditary nephropathy. Despite growing evidence for genetic heterogeneity, ADPKD diagnosis is still primarily based upon clinical imaging criteria established before discovery of additional PKD genes. This study aimed at assessing the diagnostic value of genetic verification in clinical ADPKD.

Methods

In this prospective, diagnostic trial, 100 families with clinically diagnosed ADPKD were analyzed by PKD gene panel and multiplex ligation-dependent probe amplification (MLPA); exome sequencing (ES) was performed in panel/MLPA-negative families.

Results

Diagnostic PKD1/2 variants were identified in 81 families (81%), 70 of which in PKD1 and 11 in PKD2. PKD1 variants of unknown significance were detected in another 9 families (9%). Renal survival was significantly worse upon PKD1 truncation versus nontruncation and PKD2 alteration. Ten percent of the cohort were PKD1/2-negative, revealing alternative genetic diagnoses such as autosomal recessive PKD, Birt–Hogg–Dubé syndrome, and ALG9-associated PKD. In addition, among unsolved cases, ES yielded potential novel PKD candidates.

Conclusion

By illustrating vast genetic heterogeneity, this study demonstrates the value of genetic testing in a real-world PKD cohort by diagnostic verification, falsification, and disease prediction. In the era of specific treatment for fast progressive ADPKD, genetic confirmation should form the basis of personalized patient care.

Kidney cancer characteristics and genotype-phenotype-correlations in Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHDS) is a genetic tumor syndrome characterized by lung cysts, pneumothorax, fibrofolliculomas and renal cell cancer. The diagnosis of BHDS is usually considered if kidney cancer occurs before age 50 years, is multifocal and/or bilateral or of the oncocytoma/hybrid oncocytoma-chromophobe type. Using a sample of 50 BHDS families with a total of 178 patients we analyzed how many kidney cancer patients fulfilled one or more of these criteria. Furthermore, we addressed the question if genotype-phenotype-correlations exist that can be used for risk stratification. Renal cell cancer occurred in 34/178 (19.1%) patients, and the reported male bias was not observed. Furthermore, most kidney malignancies occurred after the age of 50 years. Thus, the majority of tumors did not show the typical hallmarks of BHDS. A below-average tumor frequency (17.2%) was observed for the known mutational hotspot c.1285delC/dupC that was the cause of BHDS in 24% of families. Unexpected was the high tumor frequency (66.7%) associated with mutation c.887C>G within a single family, a finding that merits further exploration.