Background: The prediction that Duchenne muscular dystrophy patients have out-of-frame deletions and Becker muscular dystrophy patients have in-frame deletions of the dystrophin gene holds well in the vast majority of cases. Large in-frame deletions involving the rod domain only have usually been associated with mild (BMD) phenotype.
Objectives: To describe unusual cases with large in-frame deletions of the rod-shaped domain of the dystrophin gene associated with severe (Duchenne) clinical phenotype
Methods: Screening for dystrophin gene deletion was performed on genomic DNA by using multiplex polymerase chain reaction. Needle muscle biopsies from the quadriceps were obtained using a Bergström needle. The biopsies were stained with histologic and histochemical techniques as well as monoclonal antibodies to dystrophin 1, 2 and 3.
Results: In three children with large in-frame deletions of the rod domain (exons 10-44, 13-40 and 3-41), early-onset weakness and a disease course suggested the DMD phenotype.
Conclusions: This observation emphasizes the uncertainty in predicting the Becker phenotype in a young patient based on laboratory evaluation, and that the clinical picture should always be considered.