Amplification of selected exons by polymerase chain reaction enables determination of the translational reading frame of dystrophin mRNA resulting from deletion mutations.

Duchenne and Becker muscular dystrophies (DMD and BMD) are severe and mild phenotypes, respectively, of the mutated dystrophin gene. Based on the frameshift theory, an out-of-frame deletion causes DMD, while an in-frame deletion causes BMD. Amplification of deletion-prone exons by polymerase chain reaction (PCR) has been used for the screening of deletion mutations of the dystrophin gene. However, it is difficult to determine the resulting translational reading frame in deleted cases by amplification of the deletion-prone exons. To determine the resulting translational reading frame, we employed a method which selectively amplifies exons affecting the following translational reading frame. Using this method, thirty-three DMD/BMD patients with a deletion mutation in the central region of the dystrophin gene were examined. Twenty-seven of 29 DMD patients had out-of-frame deletions, while only two had in-frame deletions. All four BMD patients had in-frame deletions. Therefore, 93.9% patients fitted the frameshift theory. This method is very useful for clinical diagnosis because of its precision and convenience.