POSTN and hyperinsulinemic hypoglycemia, familial, 4: Elevated concentrations in skeletal muscle tissues have been established for the extracellular matrix components periostin (Postn), lumican (Lum), fibronectin (Fn1), collagen (Col1a2) and asporin (Asp), which is associated with reactive myofibrosis [21, 56, 148, 149], as well as increased levels of tubulin (Tubb6) and vimentin (Vim) [21, 99, 146, 150] that is indicative of cytoskeletal remodelling in response to dystrophin deficiency.