Functional validation using a zebrafish model reclassifies the rare COL1A2 p.Gly418Ala variant as a cause of Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a genetically heterogeneous skeletal dysplasia mainly caused by mutations in the COL1A1 and COL1A2 genes, which encode type I collagen. Here, using whole-exome sequencing(WES), we identified a rare heterozygous missense mutation (c.1253G > C, p.Gly418Ala) in COL1A2 in a Chinese family with recurrent prenatal skeletal dysplasia. This variant is located within the highly conserved Gly-X-Y repeat of the collagen triple-helical domain and predicted to be deleterious by bioinformatics programs. However, according to the American College of Medical Genetics and Genomics (ACMG) guidelines, it was initially classified as a variant of uncertain significance (VUS). To validate its pathogenicity, we overexpressed the mutant in a zebrafish model. The results revealed that mutant mRNA induced significant phenotypic abnormalities in zebrafish larvae, including shortened body length, axial curvature, fin malformations, and reduced vertebral mineralization-recapitulating key features of human OI. Our findings confirm the pathogenic role of the p.Gly418Ala mutation and highlight the zebrafish model as a powerful tool for rapid functional validation of VUS, facilitating clinical variant interpretation and precision medicine.