Associations between clinical phenotype (muscle weakness, dilated cardiomyopathy) and dystrophin abnormalities in muscle tissue among definite carriers of Duchenne (DMD) and Becker muscular dystrophy (BMD) were investigated.
We report three cases who presented with only mild or no muscle weakness but had elevated serum creatine kinase activity and dystrophin immunolabelling indistinguishable from normal, making a pathological diagnosis difficult.
Abnormalities of dystrophin are a common cause of muscular dystrophy and testing for dystrophin gene or protein has become a part of routine diagnostic evaluation of patients who present with progressive proximal muscle weakness, high serum creatine kinase concentrations, and histopathological evidence of a dystrophic process.
We recently described a family where a deletion of the dystrophin gene was associated with a severe dilated cardiomyopathy without skeletal muscle weakness.
We have previously shown in a large X-linked pedigree that a deletion removing the dystrophin muscle promoter, the first muscle exon and part of intron 1 caused a severe dilated cardiomyopathy with no associatedmuscle weakness.
It is speculated that overexpression of the dystrophin-related protein in regenerating muscle fibers may contribute to the slow progression of muscle weakness or atrophy.
Ten females presenting with muscle weakness and a raised serum creatine kinase revealed abnormalities in the expression of dystrophin in their muscle biopsies and were diagnosed as manifesting carriers of Xp21 Duchenne/Becker muscular dystrophy.
An apparently identical deletion in one family gave classical BMD in two brothers (presenting in their teens) and only very mild muscle weakness in their 86-year-old great-great-uncle.