TCF4 (transcription factor 4) is a sequence-specific DNA-binding transcription factor that activates gene expression by recognizing E-box motifs (5'-CANNTG-3') in target promoters. TCF4 functions as a key component of the Wnt/β-catenin signaling pathway, forming complexes with β-catenin to regulate transcription of target genes involved in cell differentiation and intestinal homeostasis 1. The protein plays critical roles in neuronal differentiation and intestinal stem cell biology, with TCF4 target genes specifically expressed in intestinal crypts 1. In disease contexts, TCF4 dysregulation contributes to multiple pathologies. In colorectal cancer, aberrant Wnt pathway activation leads to inappropriate TCF4-driven expression of oncogenic target genes 1. TCF4 mutations with microsatellite instability have been identified in leukemia and colon cancer, though frameshift mutants lose transcriptional activity 2. In gastric cancer, TCF7L2 (a TCF4 family member) promotes metastasis by transcriptionally activating PLAUR 3. TCF4 variants are also associated with type 2 diabetes risk and regulate metabolic genes controlling lipid metabolism and gluconeogenesis 4. Additionally, TCF7L2 dysfunction contributes to Paneth cell defects in Crohn's disease 5. Germline TCF4 mutations cause Pitt-Hopkins syndrome and Fuchs endothelial corneal dystrophy, highlighting its developmental importance.