MMP9 and Duchenne muscular dystrophy: 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).