Possibilities and limitations of carrier diagnosis in families with Duchenne muscular dystrophy caused by deletions in the major hot spot region using pulsed-field gel electrophoresis.

The cDNA probes cf56a, b identify deletions in 45% of the investigated patients with Duchenne and Becker muscular dystrophy (DMD/BMD). But carrier detection by junction fragments using normal gel electrophoresis conditions separating fragments up to a size of about 25 kilobases is possible only in selected cases. We, therefore, applied separation of Sfi I-digested DNA by rotating-field gel electrophoresis (RFE) in combination with Southern blot transfer and hybridization using cf56a for this purpose. In this study we compared hybridizing fragments of DNA from three DMD families with different deletion patterns: distal to the Sfi I-site F located between exon 48/49 (family A), proximal to the Sfi I-site F including the P20 intron (family B), and bridging the Sfi I-site F (family C). Junction fragments in the DNA of 2 affected boys and their mothers were detected in families B and C. Carrier determination on this basis was performed for family C. Given these three families are representative for other families with similar deletions, it will be possible to offer carrier diagnosis using RFE in 38% of the studied families with DMD/BMD caused by deletions in the major hot spot region.