Introduction
The perfect concordance between in silico prediction and in vitro experimental validation is key to elucidating the pathogenic mechanisms of novel intronic variants. In a case report detailing severe fetal encephalomalacia and subdural hemorrhage, the RDDC RNA Splicing Prediction Model (RNA Splicer) bioinformatics AI tool successfully guided subsequent functional experiments through its precise predictions. Its prediction of exon skipping was in complete agreement with the validation results from a minigene assay. This "prediction-validation" synergy provided decisive evidence for the pathogenicity of a novel intronic variant in the COL4A2 gene.
Research Challenge: WES Identifies a Non-Canonical Splice Site VUS
The challenge in this study stemmed from a fetus diagnosed with severe subdural hemorrhage and extensive encephalomalacia in the late second trimester. To determine the genetic cause, the research team performed Whole Exome Sequencing (WES) on the fetus and parents. This revealed a novel de novo heterozygous variant in the COL4A2 gene: c.549+5G>A.
Located at the +5 position of intron 8, this variant affects a non-canonical splice site, was absent from population databases, and classified as a "Variant of Uncertain Significance" (VUS). Determining its specific impact on COL4A2 mRNA splicing was crucial to understanding whether it caused the severe fetal brain injury.
RDDC's Precise Prediction: Unveiling Exon Skipping or Intron Retention
To evaluate the potential pathogenic mechanism of the c.549+5G>A variant, researchers utilized the RDDC RNA Splicing Prediction Model AI tool, along with HSF, varSEAK, and SpliceAI. RDDC's prediction provided clear and specific molecular hypotheses, indicating two primary potential aberrant splicing outcomes:
- Skipping of exon 8: The entire exon 8 would be removed during mRNA maturation.
- Intron retention: Part or all of the intron sequence would be erroneously retained.
Both predictions strongly suggested that the variant would disrupt normal mRNA processing, leading to a type IV collagen α2 chain protein that was either truncated or missing critical structural domains (like the Gly-X-Y repeats). This would likely impair collagen trimer stability and compromise vascular basement membrane integrity.
Experimental Validation: Confirming RDDC's Exon Skipping Prediction
The research team promptly proceeded to validate RDDC's predictions using an in vitro minigene assay. After transfecting HEK293T and HeLa cells with plasmids carrying the mutation, RT-PCR and sequencing showed that, unlike the wild-type construct which produced a 410 bp normal transcript, the mutant construct yielded only a single, shorter 338 bp aberrant transcript. Sequence analysis confirmed this aberrant transcript resulted from the complete skipping of exon 8 (c.478_549del).
This experimental result was in perfect agreement with the "exon 8 skipping" mode predicted by RDDC. Although this deletion (p.Pro161_Gly184del) did not cause a frameshift, the loss of 24 amino acids disrupted the integrity of the collagenous domain. The perfect match between in silico prediction and in vitro validation provided strong evidence for the pathogenicity of the c.549+5G>A variant.
Case Implications
This case highlights the power of RDDC RNA Splicer in deciphering the pathogenicity of VUS at non-canonical splice sites. It provides precise, specific molecular mechanism predictions (like exon skipping) that effectively guide subsequent functional validation experiments. It serves as a critical bridge linking genotype to severe fetal phenotypes (like brain hemorrhage and encephalomalacia), offering valuable molecular insights for the prenatal diagnosis and genetic counseling of COL4A2-related disorders.
Content Source and Disclaimer
This article is a compilation and interpretation of the scientific study cited below, intended to highlight the application of RDDC bioinformatics tools. All research data and conclusions belong to the original authors and publication.
Original Article:
Sun RY, Xu Y, Huang QQ, et al. Identification of a novel intronic variant in COL4A2 gene associated with fetal severe cerebral encephalomalacia and subdural hemorrhage. BMC Medical Genomics. 2024 Apr 24;17(1):101.
Article Link:
https://pubmed.ncbi.nlm.nih.gov/39350129/
