TCF2 encodes transcription factor 2, a liver-specific factor of the homeobox-containing basic helix-turn-helix family. The TCF2 protein is believed to form heterodimers with another liver-specific member of this transcription factor family, TCF1; depending on the TCF2 isoform, the result may be to activate or inhibit transcription of target genes. Mutation of TCF2 that disrupts normal function has been identified as the cause of MODY5 (Maturity-Onset of Diabetes, Type 5). A third human transcript variant is believed to exist based on such a variant in the rat: however, to date such an mRNA species has not been isolated.