Duchenne and Becker muscular dystrophies (DMD/BMD) are associated with mutations in the DMD gene. We determined the mutation status of 47 patients with dystrophinopathy without deletion or duplication in the DMD gene by screening performed by reverse transcription-PCR, protein truncation test, and DNA sequencing. We describe three patients with a mutation creating a premature termination codon (p.E55X, p.E1110X, and p.S3497PfsX2) but with a mild phenotype, which present three different ways of rescuing the DMD phenotype. In one patient we detected the insertion of a repetitive sequence AluYa5 in intron 56, which led to skipping of exon 57. Further, using quantitative analysis of DMD mRNA carrying various mutated alleles, we examine levels of mRNA degradation due to nonsense mediated mRNA decay. The quantity of dystrophin mRNA is different depending on the presence of a mutation leading to a premature termination codon, and position of the analysed mRNA region with respect to its 5' end or 3' end. Average relative amounts of DMD mRNAs carrying a premature termination codon is 48% and 17%, when using primers amplifying the 5' and 3' cDNA regions, respectively.