The reversible facilitated diffusion of fructose, galactose, and glucose from the cytosol to the extracellular space is mediated by the SLC2A2 (GLUT2) transporter in the plasma membrane. In the epithelial cells of the small intestine, the basolateral localisation of SLC2A2 enables hexose sugars derived from the diet (and taken up by SLC5A1 and SLC2A5 transporters into cells) to be released into the circulation. SLC2A2 is a low affinity glucose transporter expressed mainly in the kidney, liver and pancreatic beta-cells. In beta-cells, it functions as a glucose-sensor for insulin secretion and in the liver, it allows for bi-directional glucose transport. Defects in SLC2A2 can cause Fanconi-Bickel syndrome (FBS; MIM:227810), a rare but well-defined disorder characterised by glycogen accumulation, proximal renal tubular dysfunction, and impaired utilisation of glucose and galactose. Mutation in SLC2A2 causing FBS include 1bp del, R365*, R301*, P417L, V423E, Q287* and L389P (Santer et al. 1997, Burwinkel et al. 1999, Sakamoto et al. 2000).