Exons 1–3 deletion in FLCN is associated with increased risk of pneumothorax in Chinese patients with Birt-Hogg-Dubé syndrome

Background: The pathogenic variants responsible for Birt-Hogg-Dubé syndrome (BHDS) in folliculin (FLCN) gene mostly consist of point mutations. Although large intragenic deletions/duplications have been reported in several case reports, the relationship between large intragenic deletions/duplications and phenotype in BHDS remains unclear. Methods: We retrospectively identified and reviewed patients with a large intragenic deletion spanning exons 1–3 and analyzed their phenotypic features to compare with those of point mutation carriers in our hospital from January 1, 2017 to August 31, 2022. Results: Twenty unique point mutations (including 4 novel mutations) were detected in 62 patients from 45 families (90%). Exons 1–3 deletion were identified in 8 patients from 5 families (10%) that resided in the same region, Feidong County of Anhui Province, China. Breakpoint analysis indicated that all the deletion breakpoints were flanked by Alu repeats. The prevalence of exons 1–3 deletion carriers in Feidong County was 8.1-times higher than that for BHDS in Anhui Province, suggesting a clustered phenomenon of exons 1–3 deletion. Significantly increased risk of pneumothorax was observed in those with exons 1–3 deletion compared with point mutations (91% vs. 58%, p value 0.047). The risk of renal cancer may be higher in those with exons 1–3 deletion than for those with point mutations (18% vs. 4%, p > 0.05). Conclusions: Large intragenic deletion of exons 1–3 in FLCN was identified as a local aggregation phenomenon in Feidong County, China, and was associated with a significantly higher risk of pneumothorax compared to those with point mutations.