Molecular genetics of dystrophinopathy

Dystrophinopathies, including Duchenne and Becker muscular dystrophies, are caused by pathogenic variants in the DMD gene, which spans 2.5 Mb and encodes multiple tissue-specific dystrophin isoforms. Advances in molecular diagnostic techniques have expanded our ability to detect a broad spectrum of DMD variants, including exonic deletions/duplications, small variants such as single-nucleotide variants and indels, and intronic rearrangements that disrupt splicing. Transcriptomic and long-read genomic analyses have revealed previously undetectable mechanisms of variation, including pseudoexon inclusion, intronic polyadenylation, and repeat expansions, underscoring the importance of integrating RNA-level data and in silico predictions into diagnostics. Genotype-phenotype correlations are influenced by the type and location of variants and by other factors, such as naturally occurring exon skipping and modifier genes. For instance, partial dystrophin expression caused by exon skipping in patients with certain nonsense variants can result in a milder Becker-like phenotype. These findings highlight the clinical significance of functional assays, such as minigene splicing reporters and immunostaining, in refining variant interpretation. This review summarizes the spectrum of DMD variants and outlines a stepwise diagnostic approach that integrates genetic, transcriptomic, and computational data. Special consideration is given to subgroups, such as female carriers and patients with mild phenotypes, in whom molecular diagnosis can be particularly challenging. Although therapeutic strategies are not the primary focus of this article, accurate molecular diagnosis forms the foundation for guiding individualized care. Together, these insights emphasize the value of integrated multi-omic variant assessment in improving diagnostic accuracy and patient management for dystrophinopathies.