Tetrameric GLUT2, the SLC2A2 gene product, associated with the plasma membrane, mediates the facilitated diffusion of glucose (Glc) into cells. GLUT2 is expressed on hepatocytes and pancreatic beta cells, and on the basolateral surfaces of enterocytes in the small intestine. Because of its high Km for glucose (~15-20 mM), GLUT2-mediated glucose uptake increases proportionally with increase of blood glucose concentration after a meal. This feature of the transporter is thought to enable efficient uptake of large amounts of glucose by the liver in the fed state, and to allow it to function as part of a glucose sensor coupled to insulin release in pancreatic beta cells (Thorens 2001). GLUT2 also mediates glucose export from liver cells when gluconeogenesis is underway (Colville et al. 1993; Santer et al. 1997; Wu et al. 1998). GLUT2 on enterocytes mediates the release of dietary glucose, galactose, and fructose into the circulation. This activity is annotated as part of the intestinal absorption module. Defects in SLC2A2 are the cause of Fanconi-Bickel syndrome (FBS). It is characterized by hepatorenal glycogen accumulation, proximal renal tubular dysfunction, and impaired utilization of glucose and galactose (Burwinkel et al. 1999).