Variant effect on splicing regulatory elements, branchpoint usage, and
pseudoexonization: strategies to enhance bioinformatic prediction using
hereditary cancer genes as exemplars
Abstract
It is possible to estimate the prior probability of pathogenicity for
germline disease gene variants based on bioinformatic prediction of
variant effect/s. However, routinely used approaches have likely led to
the underestimation and underreporting of variants located outside donor
and acceptor splice site motifs that affect mRNA processing. This review
presents information about hereditary cancer gene germline variants,
outside native splice sites, with experimentally validated splicing
effects. We list 81 exonic variants that impact splicing regulatory
elements in BRCA1, BRCA2, MLH1, MSH2,
MSH6 and PMS2. We utilized a pre-existing large-scale
BRCA1 functional dataset to map functional splicing regulatory elements,
assess the relative performance of different tools to predict effects of
283 variants on such elements, and develop a generic workflow to
prioritize variants that may impact splicing regulatory elements. We
also describe rare examples of intronic variants that impact branchpoint
sites and create pseudoexons. We discuss the challenges in predicting
variant effect on branchpoint site usage and pseudoexonization, and
suggest strategies to improve the bioinformatic prioritization of such
variants for experimental validation. Importantly, our review highlights
the importance of considering impact of variants outside donor and
acceptor motifs on mRNA splicing and disease causation.