Splicing Characteristics of Dystrophin Pseudoexons and Identification of a Novel Pathogenic Intronic Variant in the DMD Gene

Pseudoexon (PE) inclusion has been implicated in various dystrophinopathies
however, its splicing characteristics have not been fully investigated. This study aims to analyze the splicing characteristics of dystrophin PEs and compare them with those of dystrophin canonical exons (CEs). Forty-two reported dystrophin PEs were divided into a splice site (ss) group and a splicing regulatory element (SRE) group. Five dystrophin PEs with characteristics of poison exons were identified and categorized as the possible poison exon group. The comparative analysis of each essential splicing signal among different groups of dystrophin PEs and dystrophin CEs revealed that the possible poison exon group had a stronger 3&prime
ss compared to any other group. As for auxiliary SREs, different groups of dystrophin PEs were found to have a smaller density of diverse types of exonic splicing enhancers and a higher density of several types of exonic splicing silencers compared to dystrophin CEs. In addition, the possible poison exon group had a smaller density of 3&prime
ss intronic splicing silencers compared to dystrophin CEs. To our knowledge, our findings indicate for the first time that poison exons might exist in DMD (the dystrophin gene) and present with different splicing characteristics than other dystrophin PEs and CEs.