Abstract: Objective To study the mutation and mechanism of folliculin (FLCN) gene in familial spontaneous pneumothorax (FSP). 
 Methods Clinical data were collected from three generations of patients with FSP. Computed tomography (CT) scans of the chest were used to observe the pulmonary condition. The mutation of FLCN gene in this family was detected by next generation sequencing (NGS) method. 
 Results CT scan revealed that this family developed pneumothorax or pulmonary cysts without skin lesions or kidney tumors.Through gene sequencing, it was found that the 147th amino acid of exon 6 of the FLCN gene was mutated from glutamine to a terminator (c.493C＞T) in this family of pneumothorax patients. This mutation was also shown in both patients with pneumothorax and their children. 
 Conclusion A nonsense mutation of FLCN is found in patients with FSP. This result extends the mutation spectrum of FLCN in patients with Birt-Hogg-Dubé syndrome (BHD). This may be a new mutation, and further research is needed on larger samples to understand the pathogenesis of FSP. 

Key words: pneumothorax； gene mutation； heredity