SMAD2 and keratoconus: The analysis of cornea from autopsy control and keratoconus patients using RT-PCR exhibited elevated messenger ribonucleic acid levels of Smad2 and TGF-β in severe keratoconus corneal epithelium.[58] The participation of the TGF-β pathway in the modulation and production of extracellular matrix may suggest involvement in the pathogenesis of KTCN, either in a causative role or a secondary repair response leading to structural changes in this disease.