Multilevel Molecular Analysis Identifies All Dystrophin Gene Mutations Pointing out That DMD is a Genetically Homogenous Disease: Repercussions on Diagnosis, Prevention and Therapy

Dystrophinopathies are a group of allelic diseases caused by mutation in the dystrophin (DMD) gene: Deletions (~65%), duplications (~10%), small mutations (25%) and deep intronic mutations and complex rearrangements (~1%). Many exceptions do exist to the reading frame rule and a fine genetic characterization is mandatory for providing genetic diagnosis and making patients eligible for novel personalized trials. We analyzed the dystrophin gene in a large heterogeneous cohort of 891 individuals; reasons for testing were: clinical diagnosis of DMD (485), clinical diagnosis of BMD (226), symptomatic female carriers (43), asymptomatic patient with high CK (38), limb girdle muscle dystrophy (24) and at risk females tested for known familial mutation (78). We identified the dystrophin causative mutation in all the probands except for two boys with a clinical diagnosis of DMD and absence of dystrophin in the biopsy; in both the transcript analysis pinpointed the presence of a dystrophin gene mutation. Our data demonstrate that dystrophinopathies are genetically homogenous and a multilevel diagnostic approach is able to identify all DMD mutations; therefore a monogenic NGS approach should be endorsed in this disease. These findings carry some consequences in the address and interpretation of dystrophin genetic tests in clinical genetic counseling, in the definition of the role of modifiers, in the design of new therapies and in the plan of clinical care flowcharts.