P269: Test the grandfather! Incidental in-frame DMD deletions in three asymptomatic families

The DMD gene encodes dystrophin, a protein that protects the sarcolemma from stress induced by muscle contraction and regulates other sarcolemma proteins. DMD, the largest gene in the human genome, is particularly prone to exonic deletions or duplications, causing recessive X-linked dystrophinopathies. Frameshift deletions are typically seen with Duchenne muscular dystrophy (DMD) and in-frame deletions with Becker muscular dystrophy (BMD) or DMD-associated isolated dilated cardiomyopathy (DCM). DMD in males presents in early childhood with progressive proximal muscle weakness, wheelchair dependence by early teens, markedly elevated creatine kinase (CK), and a life expectancy of 20-30 years.