Becker muscular dystrophy (BMD) is a neuromuscular disorder allelic to Duchenne 
muscular dystrophy (DMD), caused by in-frame mutations in the dystrophin gene, 
and characterized by a clinical progression that is both milder and more 
heterogeneous than DMD. Muscle magnetic resonance imaging (MRI) has been 
proposed as biomarker of disease progression in dystrophinopathies. Correlation 
with clinically meaningful outcome measures such as North Star Ambulatory 
Assessment (NSAA) and 6 minute walk test (6MWT) is paramount for biomarker 
qualification. In this study, 51 molecularly confirmed BMD patients (aged 7-69 
years) underwent muscle MRI and were evaluated with functional measures (NSAA 
and 6MWT) at the time of the MRI, and subsequently after one year. We confirmed 
a pattern of fatty substitution involving mainly the hip extensors and most 
thigh muscles. Severity of muscle fatty substitution was significantly 
correlated with specific DMD mutations: in particular, patients with an isolated 
deletion of exon 48, or deletions bordering exon 51, showed milder involvement. 
Fat infiltration scores correlated with baseline functional measures, and 
predicted changes after 1 year. We conclude that in BMD, skeletal muscle MRI not 
only strongly correlates with motor function, but also helps in predicting 
functional deterioration within a 12-month time frame.