Tandem Duplication within the DMD gene in Labrador Retrievers

A mild form of dystrophinopathy was suspected in a family of Labrador retrievers with mild or non-obvious neuromuscular clinical signs. Markedly and persistently elevated creatine kinase activity was first noted at 6 months of age. Skeletal muscle biopsies revealed a dystrophic phenotype. Dystrophin was absent on western blotting and immunohistochemical staining, with increased utrophin expression. The purpose of this study was to understand whether the molecular basis of the mild form of MD seen previously in a line of Labrador retrievers lies in an as yet undetected variant in the DMD gene, or whether the potential for variants in known modifier genes needs to be explored.