MiR-21 is another miRNA that is significantly increased in mdx mice, and its expression is significantly correlated with increased expression of fibrotic genes such as COL1A1 and COL6A. Mir-21 expression is also increased in DMD fibroblasts and further enhanced by TGF-β1 treatment. The gene discussed is COL1A1; the disease is Duchenne muscular dystrophy.