SMAD2 and keratoconus: Our gene expression analysis also indicated that several genes related to tissue fibrosis, including transforming growth factor-beta 1 and -3 (Tgf-β1 and -β3), SMAD family member 2 (Smad2), and snail family zinc finger 1, -2, and -3 (Snai1, Snai2, and Snai3), were markedly upregulated in the KC bladder.