Conversely, a positive regulation on biogenesis may also lead to tumour progression for example, TGF-β increases miR-21 maturation [51], which can act to inhibit PTEN and Sprouty 1 key negative regulators of the Akt and Ras/MAPK pathways allowing their aberrant activity [69, 70]. The gene discussed is TGFB1; the disease is neoplasm.