Genotypic characteristics of Chinese patients with BHD syndrome and functional analysis of FLCN variants

Abstract

Background Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant disease featured by lung cysts, spontaneous pneumothorax, fibrofolliculomas and renal tumors. The causative gene for BHDS is the folliculin (FLCN) gene and more than 200 mutations have been reported in FLCN, mostly truncating mutations. The aim of this study is to better characterize the clinical features and mutation spectrum of Chinese BHDS patients and to systematically evaluate the effects of non-truncating mutations on mRNA splicing pattern. Methods We enrolled 47 patients from 39 unrelated families with symptoms highly suggestive of BHDS after informed consent and detailed clinical data were collected. Exon sequencing followed by multiplex ligation-dependent probe amplification testing were applied for mutation screening. The effects of non-truncating mutations, including 15 missense mutations and 6 in-frame deletions, on mRNA splicing were investigated by minigene assays. Results A total of 24 FLCN germline variants were found in 39 patients from 31 distinct families. Out of these patients, 100% (36/36) presented with lung cysts and 58.3% (21/36) had experienced spontaneous pneumothorax. Seventeen mutation carriers had skin lesions (47.2%, 17/36) and 9 (30%, 9/30) had kidney lesions including 8 with renal cysts and 1 with renal hamartoma. Among all detected variants 14 (58.3%, 14/24) were novel, including 11 variants classified to be pathogenic and 3 variants of uncertain significance. None of 21 non-truncating mutations changed the mRNA splicing pattern of minigenes. Conclusions We found different clinical features of Chinese BHDS patients compared with Caucasians, with more lung cysts and pneumothorax but fewer skin lesions and malignant renal cancer. Chinese patients with BHDS also have a different mutation spectrum from other races. Non-truncating mutations in FLCN did not disrupt mRNA splicing pattern, in turn supporting the hypothesis that these mutations impair folliculin function by disrupting the stability of the FLCN gene product.

Identification of a Novel Pathogenic Folliculin Variant in a Chinese Family With Birt–Hogg–Dubé Syndrome (Hornstein-Knickenberg Syndrome)

“…BHDS patients in China also present with more pulmonary manifestations but fewer skin lesions and renal malignancies (Ren et al, 2008;Liu et al, 2017). Selection bias may be responsible for the different frequencies of pulmonary manifestations between Asian and Western BHDS cases (Liu et al, 2019). Most Caucasian patients with BHDS were recruited through referrals from departments of dermatology or urology, while most patients with BHDS in China were diagnosed by respiratory physicians due to the pulmonary manifestations (Liu et al, 2019).…”

“…Selection bias may be responsible for the different frequencies of pulmonary manifestations between Asian and Western BHDS cases (Liu et al, 2019). Most Caucasian patients with BHDS were recruited through referrals from departments of dermatology or urology, while most patients with BHDS in China were diagnosed by respiratory physicians due to the pulmonary manifestations (Liu et al, 2019). Patients with cutaneous fibrofolliculoma or renal neoplasms may not receive regular chest CT examinations if the patients do not have any marked respiratory symptoms.…”

New Developments in the Pathogenesis of Pulmonary Cysts in Birt–Hogg–Dubé Syndrome

“…60 The FLCN gene has 14 exons, with the coding region in exons 4 to 14. Multiple studies have defined the spectrum of FLCN mutations 20,22,32,[61][62][63] with 290 different public variants reported in the Leiden Open Variation Database updated last in October 2019. 64 The vast majority of mutations in FLCN are frameshift, nonsense, or splice site mutations.…”

“…17 Pathogenic mutations have been detected in all exons of the FLCN gene including the 5′untranslated region. 63 BHD follows Knudson's two-hit model of tumor suppression with initial studies identifying a clear somatic FLCN mutation in the majority of BHD-associated renal lesions studied. 65 Although no clear genotype-phenotype associations have been solidified for BHD, there have been trends noted with increased incidence of number of lung cysts and pneumothorax with mutations in exon 9 in one cohort.…”

Characterization of CT scans of patients with Birt-Hogg-Dubé syndrome compared with those of Chinese patients with non-BHD diffuse cyst lung diseases

“…Patients with BHD syndrome were all diagnosed by genetic testing. A total of 20 BHD patients were reported in our previous study (9), and the remaining were diagnosed from 2017 to 2019 (10). Given the relative high incidence of LAM and to avoid the selection bias of the control group, we randomly selected 33 cases using a random number table method from 297 patients with de nite LAM in the DCLD cohort at Peking Union Medical College Hospital during the same period as the selection of BHD patients.…”