Abstract: Objective · To deepen the understanding of Duchenne/Becker muscular dystrophyinvestigating dystrophin (DMD) gene variants in 2 Chinese Han families with this disease. Methods · Retrospective analysis of the clinical characteristics of the probands in two families with Duchnne/ Becker muscular dystrophy and the results of multiplex ligation-dependent probe amplification (MLPA) for the probands and their relatives was performed. Results · Three probands were identifiedsignificantly-elevated creatine kinase levels. Two probands in family one are fraternal twin brothers with the same deletions of exons 8-9, while their mother has no abnormality at this site. The proband in family two is the little brother in a pair of fraternal twins with duplication of exons 48-51, and his mother has heterozygous duplication of exons 48-51. Conclusion · ① The presence of the same DMD gene mutation in the fraternal twins suggests that the mother may be a gonad chimera with this mutation if her gene detection of peripheral blood is normal. The mother must undergo prenatal gene diagnosis to reduce the risk of Duchenne/Becker muscular dystrophy in her offsprings. ② The exons 48-51 duplication of DMD gene is pathogenic mutation.

Key words: Duchenne/Becker muscular dystrophy, dystrophin gene, gene mutation, multiplex ligation-dependent probe amplification (MLPA), fraternal twins, creatine kinase