SPARC and Duchenne muscular dystrophy: Two biomarkers of muscle fibrosis, nidogen and ON/SPARC, showed moderate association with DMD versus normal mRNA (−4.8-fold and − 3.6-fold change in normal, respectively) and with histological severity (r = −0.52, r = −0.54), as is expected given that fibrosis is a major determinant of histological severity (indeed, these mRNAs serve as a positive control for biopsies).