Beyond Coding Variants: RNA-Level Mechanisms in Human Disease and Precision Therapeutics.

Clinical genomics has traditionally focused on protein-coding variation, yet many pathogenic mechanisms arise through alterations in RNA processing, stability, localisation, translation, and surveillance. Prior reviews have addressed individual RNA layers, splicing, non-coding RNAs, RNA therapeutics, or RNA diagnostics in isolation. This review presents an integrated, mechanism-matched framework linking RNA-level disease mechanisms to diagnostic reasoning and therapeutic selection across all major RNA layers, offering a practical resource for clinical geneticists and translational researchers. I examine how splicing defects, pseudoexon inclusion, polyadenylation disruption, RNA editing loss, untranslated-region variants, premature termination codons, stop-loss variants, RNA-binding protein dysfunction, non-coding RNA dysregulation, altered codon usage, ribosome stalling, and surveillance pathway failure, including nonsense-mediated decay, nonstop decay, and no-go decay, each create distinct and mechanistically addressable disease states. A central argument of this review is that treatment selection must be mechanism-matched rather than gene- or variant-class-based: splice defects may require antisense oligonucleotide (ASO)-mediated correction or small-molecule splice modulation; toxic transcripts may require ASO- or siRNA-mediated silencing; haploinsufficiency may require mRNA replacement or transcript rescue; premature termination codons are candidates for readthrough only when transcript and protein context are favourable. I further argue that RNA sequencing, long-read transcriptomics, allele-specific expression analysis, and functional assays are essential for both diagnosis and therapeutic stratification. The framework described here moves clinical variant interpretation beyond descriptive classification toward mechanism-based, RNA-centric precision medicine.