Normal and altered pre-mRNA processing in the DMD gene.

Splicing of pre-mRNA is a crucial regulatory stage in the pathway of gene expression controlled by multiple post- and co-transcriptional mechanisms. The large Duchenne muscular dystrophy gene encoding the protein dystrophin provides a striking example of the complexity of human pre-mRNAs. In this review, we summarize the current state of knowledge about canonical and non-canonical splicing in the DMD pre-mRNA, with a focus on mechanisms that take place in the full-length transcript isoform expressed in human skeletal muscle. In particular, we highlight recent work demonstrating that multi-step events are required for long DMD intron removal. The role of temporary intron retention in the occurrence of alternative splicing events is also discussed. Even though the proportion of splicing mutations is lower than reported in other genes, a great diversity of splicing defects linked to point mutations, but also large genomic rearrangements are observed in the DMD gene. We provide an overview of the molecular mechanisms underlying aberrant splicing in patients with Duchenne or Becker muscular dystrophy, and we also detail how alternative splicing can serve as a disease modifier in patients by changing the outcome of the primary defect.