MLPA Analyses Reveal a Spectrum of Dystrophin Gene Deletions/Duplications in Pakistani Patients Suspected of Having Duchenne/Becker Muscular Dystrophy: A Retrospective Study

Introduction: Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are inherited X-linked recessive genetic disorders caused by defects in the dystrophin gene. Abnormality in the dystrophin protein causes progressive muscle damage and weakness leading to long-term disability. Objective: To investigate the spectrum of dystrophin gene variants (deletions and duplications) in Pakistani patients suspected of having DMD/BMD or of being DMD/BMD carriers. Methods: A single center (Aga Khan University Hospital, Karachi, Pakistan) retrospective review of 46 cases was conducted to characterize dystrophin gene variants (deletion/duplication) in DMB/BMD patients using the multiplex ligation-dependent probe amplification-based method to provide coverage for all 79 exons. Results: Dystrophin gene deletions were identified in 40 of 46 cases, whereas duplications were present in 6 of 46 cases. The majority of the deletions were present between exons 45 and 52 followed by the region between exons 8 and 18. The most frequently deleted was exon 46 (8%) followed by exon 49 (7%). Dystrophin gene duplications were clustered between exons 3 and 7. The average deletion or duplication size was five exons for both kinds of variants. Conclusions: The applicability of exon skipping drugs depends on the specific mutational frequencies within populations. Our data suggest that for the Pakistani patients, multiple exon skipping between exons 46 and 49 could potentially be a target for exon skipping therapy. However, a larger nationwide study is required to further identify the predominant deletion/duplication dystrophin gene variants present in the population.