Genetic diagnosis and variant spectrum in 940 patients with Duchenne and Becker muscular dystrophies

Abstract Background Duchenne and Becker muscular dystrophies are allelic X-linked dystrophinopathies caused by DMD pathogenic variants. Accurate delineation of the variant spectrum is required for molecular diagnosis, reproductive counseling, and assessment of eligibility for mutation-specific therapies. Objective To analyze the DMD variation spectrum and evaluate the diagnostic performance and limitations of a sequential multiplex ligation-dependent probe amplification (MLPA)-first, exome sequencing (ES)-second testing strategy in a large single-center cohort of patients with Duchenne and Becker muscular dystrophies. Methods The 940 probands (924 males and 16 females, with ages ranging from birth to 54 years) underwent initial screening for large deletions and duplications using multiplex ligation-dependent probe amplification (MLPA), with negative cases and single exon cases subsequently analyzed by exome sequencing (ES) for small variants. Maternal segregation analysis was performed in 888 families for which maternal samples were available to determine whether the identified DMD variants were maternally inherited or presumed de novo. Results A DMD variant was identified in 921 of 940 genetically or pathologically confirmed cases (97.98%). Among the 921 molecularly diagnosed cases, large deletions, large duplications, small sequence variants, and complex structural variants accounted for 66.34% (611/921), 11.73% (108/921), 20.63% (190/921), and 1.30% (12/921), respectively. From 921 cases, twelve complex structural variants, including combined deletion-duplication events, discontinuous duplications, and inversions, were identified. The 16 females with heterozygous DMD variants showed variable findings, ranging from no reported symptoms to elevated creatine kinase CK levels and clinically manifesting dystrophinopathy. Nineteen patients with biopsy-supported dystrophinopathy remained molecularly unresolved. Conclusion The MLPA and ES strategy could identified DMD variants in most genetically or pathologically confirmed cases. These findings refine the contemporary DMD variant spectrum in a Chinese referral cohort and support molecular diagnosis, family-based interpretation, genetic counseling, and assessment of eligibility for mutation-specific therapies.