We hypothesized that GDF-8 that prevents hypertrophy [28,29] and FSTN its inhibitory counterpart [30], together with MMP-2, MMP-9 and TIMP-1 may serve as biomarkers in DMD, so herein we evaluated serum levels of GDF-8, FSTN, MMP-9, MMP-2 and TIMP-1 in DMD steroid naïve patients, patients under steroid treatment and their female relatives in order to assess their potential applicability as non-invasive biomarkers, and trying to refine the role of these biomolecules in the pathology, as it is very crowded and complex (Figure 1). Here, MSTN is linked to Duchenne muscular dystrophy.