The frequency of patients with dystrophin abnormalities in a limb-girdle patient population

Of the 3,048 diagnostic muscle biopsies processed by the National Institute of Neuroscience, Tokyo, over 12 years, 41 cases carried the clinical diagnosis of limb-girdle muscular dystrophy. We have analyzed all 41 cases for dystrophin content in muscle by both immunofluorescence and immunoblot. We identified five male patients with an abnormal dystrophin pattern diagnostic of Becker muscular dystrophy, and two female patients with dystrophin patterns consistent with a manifesting carrier of Duchenne muscular dystrophy diagnosis. Thus, 17% of our limb-girdle patients showed a dystrophinopathy, indicating that they in fact had a disorder related to Duchenne/Becker muscular dystrophy. Misclassification of isolated male limb-girdle patients was 31% (4/13), while misclassification of isolated female limb-girdle patients was 13% (2/15). Using multiplex polymerase chain reaction analyses of small amounts of muscle biopsy DNA confirmed a dystrophin gene deletion in all five male Becker dystrophy patients identified. This study emphasizes the clinical overlap between limb-girdle muscular dystrophy and dystrophinopathies, and reinforces the necessity of dystrophin protein and gene studies for the accurate clinical diagnosis of isolated cases of muscular dystrophy.