Duchenne and Becker muscular dystrophy are part of a spectrum of disease now more correctly called dystrophinopathies, as they are due to genetic faults (mutations) in a gene called dystrophin. Duchenne muscular dystrophy (DMD) usually presents in early childhood with delayed motor milestones including delays in walking independently. Affected boys have a waddling gait and difficulty climbing stairs. DMD is rapidly progressive, while Becker muscular dystrophy (BMD) is characterised by later-onset skeletal muscle weakness, with symptoms starting up to the age of 30 years.
The clinical severity is broadly correlated with the type of genetic fault in the gene. Large deletions may lead to absence of dystrophin expression in muscle tissue. This is usually associated with DMD. When a genetic fault results in partial dystrophin protein remaining, the milder BMD phenotype occurs. Therefore, the type of genetic fault can distinguish between the DMD and BMD phenotypes with high, but not perfect, accuracy.
Parents often hope that testing will give them the information that their little boy with clinical features will have BMD rather than DMD. Importantly the clinical phenotype will not be changed by a genetic result.