Identification and functional validation of a novel FBN1 variant in a Marfan syndrome family using a zebrafish model.

Background: Marfan syndrome (MFS) is an inherited autosomal dominant disorder that affects connective tissue with an incidence of about 1 in 5,000 to 10,000 people. 90% of MFS is caused by mutations in the fibrillin-1 (FBN1) gene. We recruited a family with MFS phenotype in South China and identified a novel variant. This study investigated whether this genetic variant is pathogenic and the potential pathway related to lipid metabolism in MFS.

Methods: A three-generation consanguineous family was recruited for this study. Whole exome sequencing (WES) was utilized on family members. The 3D structure of the protein was predicted using AlphaFold. CRISPR/Cas9 was applied to generate a similar fbn1 nonsense mutation (fbn1^+/-) in zebrafish. RNA-seq analysis on zebrafish was performed to identify potential pathways related to MFS pathogenesis.

Results: Our study identified a novel variant [NM_000138.5; c.7764 C > G: p.(Y2588*)] in FBN1 gene from the family and identified the same site mutation among the proband along with her son and daughter. Structural modeling showed the p.Y2588* mutation resulted from a truncated protein. Compared to wild-type zebrafish, the F2 generation fbn1^+/- zebrafish exhibited MFS phenotype. RNA-seq analysis indicated that many genes related to leptin are up-regulating, which could affect bone development and adipose homeostasis.

Conclusion: A novel variant was identified in FBN1 gene. In a zebrafish model, we found functional evidence supporting the pathogenicity of the detected nonsense mutation. Our research proposes a possible mechanism underlying the relationship between lipid metabolism and MFS. These findings can help improve the clinical diagnosis and treatment of MFS.