Introduction
Deep intronic variants (DIVs) represent a significant challenge in genetic diagnostics, often missed by Whole Exome Sequencing (WES). However, these seemingly "silent" variants can cause severe disease by disrupting mRNA splicing. A recent study on Fabry Disease (FD) perfectly illustrates the pivotal role of the RDDC RNA Splicer tool in tackling this challenge. In this research, RDDC provided a precise prediction for a novel DIV in the GLA gene. This prediction was not only successfully validated by a minigene assay but also led to the discovery of an unprecedented dominant-negative pathogenic mechanism.
The Clinical Challenge: A WES-Negative Deep Intronic Variant
The study began with a 60-year-old male patient clinically diagnosed with Fabry disease (cardiac involvement, very low GLA enzyme activity), yet WES failed to identify any pathogenic variants. Undeterred, the research team used targeted Sanger sequencing and uncovered a novel variant deep within an intron of the GLA gene: c.640–814T>C.
This was a classic DIV with unknown functional consequences. How could the team prove that this variant, located in the "dark matter" of the genome, was the culprit behind the patient's Fabry disease?
RDDC's Precise Prediction: Unveiling Pseudoexon Insertion
To investigate the function of the c.640–814T>C variant, the team utilized the RDDC RNA Splicer tool for splicing prediction. RDDC's analysis yielded a clear and specific mechanistic hypothesis: the variant would cause an intronic sequence to be mistakenly recognized and spliced, leading to the insertion of a 57 bp pseudoexon into the mature mRNA.
This prediction pointed directly to the subsequent molecular event: the pseudoexon insertion would cause a frameshift, resulting in a truncated, non-functional GLA protein (p.Pro214SerfsTer10).
Perfect Validation by Minigene Assay and Mechanistic Innovation
The research team promptly validated RDDC's prediction using an in vitro minigene assay. The experimental results perfectly matched the RDDC prediction: the construct carrying the c.640–814T>C variant indeed produced an aberrant mRNA containing the 57 bp pseudoexon insertion.
Further investigation revealed a novel finding: although this truncated GLA protein lacked enzymatic activity, it could still form heterodimers with the wild-type GLA protein. Through a dominant-negative effect, it significantly inhibited the activity of the wild-type enzyme (by 47.2%). This was the first time a truncated GLA protein was shown to cause disease via this mechanism.
Case Implications
This case powerfully demonstrates that RDDC RNA Splicer is a formidable tool for uncovering and dissecting the pathogenicity of deep intronic variants. In WES-negative cases, combining targeted sequencing with RDDC's precise predictions can effectively identify hidden pathogenic variants. The specific splicing pattern predicted by RDDC (e.g., pseudoexon insertion) provides clear targets for functional experiments, successfully revealing a novel pathogenic mechanism for Fabry disease and offering crucial insights for the precise diagnosis and therapeutic strategies for rare diseases.
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:
Zhang H, Zhang Y, Zhou N, et al. c.640–814T>C mutation in deep intronic region of alpha-galactosidase A gene is associated with Fabry disease via dominant-negative effect. Journal of Medical Genetics. 2024 Feb 19;61(3):284-288.
Article Link: https://pubmed.ncbi.nlm.nih.gov/39613053/
