MMP9 and Duchenne muscular dystrophy: The increased abundance of the matrix metalloproteinase MMP9 agrees with the findings from the previous screening of serum from the mdx mouse and patients with Duchenne muscular dystrophy for minimally invasive biomarker candidates (Nadarajah et al., 2011; Hathout et al., 2014; Anaya-Segura et al., 2015).