The E-protein TCF4 (also called E2-2 and ITF2), which is a class I basic helix-loop-helix (bHLH) transcription factor, is involved in the pathogenesis of Fuchs’ endothelial corneal dystrophy, primary sclerosing cholangitis, Pitt–Hopkins syndrome, and several types of malignant tumours [21]. The gene discussed is TCF4; the disease is sclerosing cholangitis.