Undetectable dystrophin can still result in a relatively benign phenotype of dystrophinopathy.

We present here a 28-year-old male patient with Becker muscular dystrophy whose skeletal muscle showed an absence of dystrophin. He has had progressive and predominantly proximal muscular wasting since 5 years of age, but was able to walk until 26 years of age. He showed hypertrophic calves, cardiomyopathy, and an elevated serum creatine kinase level (934 U/1). A skeletal muscle biopsy revealed advanced chronic myopathic changes. Immunohistochemical examination using anti-dystrophin antibodies against C-terminus showed deficiency of the protein. Rod domain and N-terminus were also absent in almost all muscle fibers, but only in a small part of the sample, they were faintly stained. beta-Dystroglycan and utrophin were present only in a small number of muscle fibers. DNA and RT-PCR analysis showed a frame-shift deletion of exons 3-7 in the dystrophin gene. In such an exceptional case as this one, it is important to investigate the factors which determine the severity of dystrophinopathy.