Novel Non-contiguous Duplications in the DMD Gene in Five Patients with Duchenne Muscular Dystrophy

ABSTRACT

BACKGROUND: Muscular dystrophy is an X-linked recessive disorder caused by mutations in the DMD gene. Muscular dystrophy is classified into 2 types; Duchenne muscular dystrophy (DMD), which has severe clinical symptoms, and Becker muscular dystrophy (BMD), which has much milder clinical symptoms. Phenotypic progression to either DMD or BMD can be predicted by analyzing mutations in DMD by using the reading frame rule. METHODS: Of 88 patients with mutations in DMD, which were detected using Multiplex Ligation-dependent Probe Amplification DMD test kit (MRC-Holland, The Netherlands), medical records of 5 patients with non-contiguous duplications were reviewed. These rare non-contiguous duplications in DMD were compared with those reported previously. RESULTS: We identified 3 novel non-contiguous duplications in DMD that included exons 2-7 and 45-51, exons 5-37 and 50-59, and exons 52-53 and 56-61. The 5 patients with these non-contiguous duplications showed the phenotypic features of DMD. Especially, duplication of exons 52-53 and 56-61 was observed in a family, i.e., 2 DMD-affected brothers and their carrier mother. CONCLUSIONS: Prediction of phenotypes associated with complex non-contiguous duplications by using the reading frame rule is difficult because the duplications affect the expression of DMD together. Because most patients with non-contiguous duplications showed the phenotypic features of DMD, the reading frame rule should be interpreted cautiously. This study provides important insights on the non-contiguous duplications in DMD for understanding genotype-phenotype correlations and for developing dystrophin for therapeutic purposes.