Interplay between DMD Point Mutations and Splicing Signals in Dystrophinopathy Phenotypes

Abstract

DMD nonsense and frameshift mutations lead to severe Duchenne muscular dystrophy while in-frame mutations lead to milder Becker muscular dystrophy. Exceptions are found in 10% of cases and the production of alternatively spliced transcripts is considered a key modifier of disease severity. Several exonic mutations have been shown to induce exon-skipping, while splice site mutations result in exon-skipping or activation of cryptic splice sites. However, factors determining the splicing pathway are still unclear. Point mutations provide valuable information regarding the regulation of pre-mRNA splicing and elements defining exon identity in the DMD gene. Here we provide a comprehensive analysis of 98 point mutations related to clinical phenotype and their effect on muscle mRNA and dystrophin expression. Aberrant splicing was found in 27 mutations due to alteration of splice sites or splicing regulatory elements. Bioinformatics analysis was performed to test the ability of the available algorithms to predict consequences on mRNA and to investigate the major factors that determine the splicing pathway in mutations affecting splicing signals. Our findings suggest that the splicing pathway is highly dependent on the interplay between splice site strength and density of regulatory elements.

DMD Mutations in 576 Dystrophinopathy Families: A Step Forward in Genotype-Phenotype Correlations

“…Small mutations also present numerous exceptions to the reading frame rule, especially in BMD patients, in whom most exceptions are due to alterations in the normal splicing pattern [ 39 ]. All nonsense or frameshift mutations associated with BMD are located in in-frame exons (exons 9, 28, 37, 71 and 74).…”

“…The 11.9-fold difference in the number of CpG transitions compared to non-CpG transitions is similar to that obtained by measuring the divergence between humans and chimpanzees, observed to be 10 times higher for CpG sites [ 79 ]. According to previous publications [ 39 ], there are no hot spots for small insertions/deletions, although the study of the mutated sequence reveals that in most cases the presence of repeated motifs is implicated in the etiology of such mutations.…”

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

“…Auxiliary SREs are preferentially located near the splice sites and include exonic splicing silencers (ESSs), exonic splicing enhancers (ESEs), intronic splicing silencers (ISSs), and intronic splicing enhancers (ISEs) [ 6 , 7 ]. Those pathogenic intronic variants can cause various non-canonical splicing events of dystrophin pre-mRNA by affecting essential or auxiliary splicing cis -elements, including exon-skipping, intron retention, cryptic splice site activation, and pseudoexon (PE)-inclusion [ 2 , 3 , 4 , 8 , 9 ]. Among the aberrant non-canonical splicing events reported in the DMD gene, PE inclusion has been frequently described to be involved in the pathogenesis of dystrophinopathies [ 3 , 9 , 10 ].…”

Identification of Exonic Copy Number Variations in Dystrophin Gene Using Mlpa / Identificarea Variaţiilor Numărului de Copii în Gena Distrofinei Folosind Metoda Mlpa

“…Dystrophinopathies include a spectrum of neuromuscular disorders, caused by mutations in the DMD gene that encodes for dystrophin, which is a key element for sarcolemma stability during muscle contraction (1). Duchenne muscular dystrophy (DMD; MIM# 310200) is the most severe form, being characterized by progressive symmetrical muscle weakness, calf pseudohypertrophy (before age 5), wheelchair dependency by age 12, and death in the 2 nd -3 rd decade due to heart or respiratory failure.…”