Pathogenic variants that alter protein code often disrupt splicing

William Fairbrother and colleagues use a massively parallel splicing assay (MaPSy) to analyze 4,964 exonic, disease-causing mutations for splicing defects in vivo and in vitro . They find that 10% of these exonic mutations affect splicing, and they classify these alterations by the stage of spliceosome assembly that is disrupted. The lack of tools to identify causative variants from sequencing data greatly limits the promise of precision medicine. Previous studies suggest that one-third of disease-associated alleles alter splicing. We discovered that the alleles causing splicing defects cluster in disease-associated genes (for example, haploinsufficient genes). We analyzed 4,964 published disease-causing exonic mutations using a massively parallel splicing assay (MaPSy), which showed an 81% concordance rate with splicing in patient tissue. Approximately 10% of exonic mutations altered splicing, mostly by disrupting multiple stages of spliceosome assembly. We present a large-scale characterization of exonic splicing mutations using a new technology that facilitates variant classification and keeps pace with variant discovery.