Duchenne and Becker muscular dystrophies,due to genovariation of the dystrophin gene,are X-linked recessively inherited progressive neuromuscular diseases and affect mainly male individuals.While it is estimated that 20％ of female carriers may have various symptoms.The clinical picture of carriers includes muscle weakness,cardiac involvement,cognitive impairment and muscle cramps/myalgias,as well as an elevated serum creatine kinase level and dystrophin abnormalities in muscle tissue.Apart from some cases associated with chromosome aberrations,the pathogenesis in most female carriers are caused by skewed X inactivation.Given the low incidence of manifesting carriers and the wide spectrum of phenotypes,the diagnosis and treatment may be delayed.In addition,there is little experience to guide management and predict prognosis.