Genetic, epidemiologic and clinicopathologic studies of Japanese Asian patients with Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome (BHD) is a rare genetic disorder characterized by fibrofolliculomas, pulmonary cysts and renal cell carcinomas (RCCs). The affected individuals inherit germline mutations in the folliculin gene (FLCN). We investigated the mutation spectrum and clinicopathologic findings of 312 patients from 120 different families (119 Japanese and 1 Taiwanese). A total of 31 different FLCN sequence variants were identified. The majority were c.1285dupC (n = 34), c.1533_1536delGATG (n = 25), and c.1347_1353dupCCACCCT (n = 19). Almost all patients presented with pulmonary cysts. The incidence of RCCs in FLCN mutation carriers over the age of 40 was 34.8% (40/115). Fifty-five RCC lesions were surgically resected; most were either chromophobe RCC (n = 24; 43.6%) or hybrid oncocytic/chromophobe tumors (19; 34.5%). Seventy-six of 156 FLCN mutation carriers (120 probands and 36 sibs, 48.7%) had skin papules; however, cutaneous manifestations were so subtle that only one patient voluntarily consulted dermatologists. Japanese Asian BHD families have three FLCN mutational hotspots. Recurrent episodes of pneumothoraces are the major symptoms suggestive of a BHD diagnosis in our cohort. Characteristic features of lung and kidney lesions may be more informative than fibrofolliculomas as diagnostic criteria for BHD in the Japanese Asian population.

Furuya M ，Yao M ，Tanaka R ，Nagashima Y ，Kuroda N ，Hasumi H ，Baba M ，Matsushima J ，Nomura F ，Nakatani Y ... -  《-》

Pathology of Birt-Hogg-Dubé syndrome: A special reference of pulmonary manifestations in a Japanese population with a comprehensive analysis and review.

Birt-Hogg-Dubé (BHD) syndrome is a rare genetic disorder characterized by cutaneous fibrofolliculomas, pulmonary cysts and renal cell carcinomas. Affected individuals inherit germline mutations in the folliculin gene (FLCN). Approximately 150 pathogenic FLCN variants have been identified worldwide. Many Japanese probands of BHD syndrome were first identified by pulmonologists and/or radiologists during treatment of pneumothoraces. Lung specimens obtained through video-assisted thoracoscopic surgery (VATS) have characteristic features unique to BHD syndrome; however, pathologists often miss key findings and diagnose patients with "bullae/blebs". The pleural and subpleural cysts of BHD syndrome-associated lung diseases are often modified by tissue remodeling and can be difficult to distinguish from emphysematous bullae/blebs. Intraparenchymal unruptured cysts tend to retain distinctive features that are different from other cystic lung diseases. Here, we review the clinicopathological findings of BHD syndrome in a Japanese population based on data from 200 probands diagnosed by genetic testing and a total of 520 symptomatic family members identified through BHD-NET Japan (http://www.bhd-net.jp/). Detailed morphology of pulmonary cysts obtained from VATS and autopsied lung specimens are described, and pathological clues for differentiating miscellaneous cystic lung disorders are discussed.

Furuya M ，Nakatani Y 《-》

Distinctive expression patterns of glycoprotein non-metastatic B and folliculin in renal tumors in patients with Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome (BHD) is an inherited disorder associated with a germline mutation of the folliculin gene (FLCN). The affected families have a high risk for developing multiple renal cell carcinomas (RCC). Diagnostic markers that distinguish between FLCN-related RCC and sporadic RCC have not been investigated, and many patients with undiagnosed BHD fail to receive proper medical care. We investigated the histopathology of 27 RCCs obtained from 18 BHD patients who were diagnosed by genetic testing. Possible somatic mutations of RCC lesions were investigated by DNA sequencing. Western blotting and immunohistochemical staining were used to compare the expression levels of FLCN and glycoprotein non-metastatic B (GPNMB) between FLCN-related RCCs and sporadic renal tumors (n = 62). The expression of GPNMB was also evaluated by quantitative RT-PCR. Histopathological analysis revealed that the most frequent histological type was chromophobe RCC (n = 12), followed by hybrid oncocytic/chromophobe tumor (n = 6). Somatic mutation analysis revealed small intragenic mutations in six cases and loss of heterozygosity in two cases. Western blot and immunostaining analyses revealed that FLCN-related RCCs showed overexpression of GPNMB and underexpression of FLCN, whereas sporadic tumors showed inverted patterns. GPNMB mRNA in FLCN-related RCCs was 23-fold more abundant than in sporadic tumors. The distinctive expression patterns of GPNMB and FLCN might identify patients with RCCs who need further work-up for BHD.

Furuya M ，Hong SB ，Tanaka R ，Kuroda N ，Nagashima Y ，Nagahama K ，Suyama T ，Yao M ，Nakatani Y ... -  《-》

Heterozygous germline FLCN mutation in Birt-Hogg-Dubé syndrome with bilateral renal hybrid oncocytic/chromophobe tumor and unilateral renal chromophobe cell carcinoma: a case report.

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant tumor syndrome caused by Folliculin (FLCN) gene mutation. The clinical manifestations are diverse, and the renal tumor is the most serious. We report the case of a 51-year-old female with multiple space-occupying lesions in both kidneys, as well as bilateral renal cysts and multiple lung cysts. The resected tumors were finally diagnosed as bilateral renal hybrid oncocytic/chromophobe tumor (HOCT) and unilateral chromophobe cell carcinoma. A history of pneumothorax surgery 4 years ago was convinced. All of these strongly suggested the possibility of BHD syndrome. Gene test confirmed a heterozygous germline FLCN nonsense mutation (c.1429C > T, p.Arg477Ter). The patient is still doing well after 20 months of follow-up (cut-off date July 2022). This is a case of BHD syndrome presented with bilateral renal tumor, renal cysts, and multiple lung cysts, and confirmed by gene testing. Patients with any combination of one or more of the manifestations should remain alert to the BHD syndrome. Our report will help to deepen the understanding of the clinicopathological features and molecular changes of BHD syndrome.

Li J ，Liu F ，Liu X ，Hu Y ，Liu Z ，Shen Y ，Wan J ... -  《-》

Fluorescent and chromogenic in situ hybridization of CEN17q as a potent useful diagnostic marker for Birt-Hogg-Dubé syndrome-associated chromophobe renal cell carcinomas.

Birt-Hogg-Dubé syndrome (BHD) is a familial disorder associated with a germline mutation of FLCN that is a tumor suppressor gene. Patients with BHD have high risks for developing multiple renal cell carcinomas (RCCs). The frequent histological types are hybrid oncocytic/chromophobe tumors (HOCTs) and chromophobe RCCs. The morphology of HOCTs could alert pathologists to the possibility of BHD. On the other hand, chromophobe RCCs occurring in BHD patients demonstrate positive immunostaining for cytokeratin-7, CD82, and Ksp-cadherin similar to their sporadic counterparts. Highly reliable markers for BHD-associated chromophobe RCCs have not been identified. In the present study, we analyzed the state of chromosome 17 in 18 renal tumors composed of 8 chromophobe RCCs, 7 HOCTs, and 3 papillary RCCs obtained from BHD patients using fluorescent and chromogenic in situ hybridization probes for the centromeric region of chromosome 17 long arm. All chromophobe RCCs and HOCTs were disomic except for 1 chromophobe RCC that showed monosomy. On the other hand, 12 of 14 sporadic chromophobe RCCs were monosomic (P = .0008). The state of chromosomes 2 and 6 were also statistically different (P = .0074 and P = .0007, respectively). Three BHD-associated papillary RCCs demonstrated either trisomy (n = 2) or disomy (n = 1). Three of 5 sporadic papillary RCCs showed trisomy. The results indicate that fluorescent and chromogenic in situ hybridization of the centromeric region of chromosome 17 long arm should be a potent useful marker for chromophobe RCCs in patients who have not been diagnosed with BHD and thereby help to determine whether the cases should be considered for genetic testing.

Kato I ，Iribe Y ，Nagashima Y ，Kuroda N ，Tanaka R ，Nakatani Y ，Hasumi H ，Yao M ，Furuya M ... -  《-》