A 400-kb tandem duplication within the dystrophin gene leads to severe Becker muscular dystrophy.

We describe a family with a large duplication of exons 2-16 of the dystrophin gene. It was characterized by immunocytochemistry, field-inversion gel electrophoresis and quantitative Southern blots. Our observations are of clinical interest in that they demonstrate an intermediate disease course despite a disrupted reading frame of dystrophin as postulated from exon-intron boundaries. We discuss possible mechanisms which may explain the unusual phenotype in our patient.