Duchenne muscular Dystrophy (DMD) is an inherited disease caused by mutations in 
the dystrophin gene that disrupt the open reading frame, while in frame 
mutations result in Becker muscular dystrophy (BMD). Ullrich congenital muscular 
dystrophy (UCMD) is due to mutations affecting collagen VI genes. Specific 
muscle miRNAs (dystromirs) are potential non-invasive biomarkers for monitoring 
the outcome of therapeutic interventions and disease progression. We quantified 
miR-1, miR-133a,b, miR-206 and miR-31 in serum from patients with DMD, BMD, UCMD 
and healthy controls. MiR-1, miR-133a,b and miR-206 were upregulated in DMD, but 
unchanged in UCMD compared to controls. Milder DMD patients had higher levels of 
dystromirs than more severely affected patients. Patients with low forced vital 
capacity (FVC) values, indicating respiratory muscle weakness, had low levels of 
serum miR-1 and miR-133b. There was no significant difference in the level of 
the dystromirs in BMD compared to controls. We also assessed the effect of 
dystrophin restoration on the expression of the five dystromirs in serum of DMD 
patients treated systemically for 12 weeks with antisense oligomer eteplirsen 
that induces skipping of exon 51 in the dystrophin gene. The dystromirs were 
also analysed in muscle biopsies of DMD patients included in a single dose 
intramuscular eteplirsen clinical trial. Our analysis detected a trend towards 
normalization of these miRNA between the pre- and post-treatment samples of the 
systemic trial, which however failed to reach statistical significance. This 
could possibly be due to the small number of patients and the short duration of 
these clinical trials. Although longer term studies are needed to clarify the 
relationship between dystrophin restoration following therapeutic intervention 
and the level of circulating miRNAs, our results indicate that miR-1 and miR-133 
can be considered as exploratory biomarkers for monitoring the progression of 
muscle weakness and indirectly the remaining muscle mass in DMD.