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

Keqiang Liu,Xinlun Tian,Wenshuai Xu,Jiaxing Song,Xue Zhang,Meng Xiao,Qianli Zhang,Yaping Liu,Xinyue Zhao,Kai-Feng Xu,Tao Qu

doi:10.1186/s13023-019-1198-y

Abstract

BackgroundBirt-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.MethodsWe 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.ResultsA 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.ConclusionsWe 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.

Highlights

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant disease featured by lung cysts, spontaneous pneumothorax, fibrofolliculomas and renal tumors
We described the clinical and genetic features of a cohort of 39 Chinese BHDS patients from 31 distinct families, and systematically evaluated the effect of all FLCN missense and in-frame mutations reported in Human Genome Mutation Database (HGMD) database on mRNA splicing pattern
Clinical features of Chinese BHDS patients A total of 39 patients (37 Females, 2 Males) from 31 distinct families were diagnosed with BHDS by genetic testing (Table 1)

Summary

Introduction

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant disease featured by lung cysts, spontaneous pneumothorax, fibrofolliculomas and renal tumors. Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant inherited disorder caused by germline mutations in the folliculin (FLCN) gene [1], which encodes a tumor suppressor protein. The symptoms of skin, pulmonary, and renal appear independently with high association, and BHDS patients can present with a single phenotype or a combination of any of them [2]. This combination contributes to the great variability in clinical features of BHD syndrome, making clinical diagnosis generally difficult. Further studies are warranted to better understand the clinical and genetic characteristics of Chinese BHDS patients

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