In a Turkish patient, born to consanguineous parents, with renal glucosuria (GLYS; 233100), van den Heuvel et al. (2002) found a homozygous G-to-A transition at position 1320 within exon 11 of the SGLT2 gene, resulting in a change in codon 440 from TGG (trp) to TGA (ter). The mutation resulted in a truncated SGLT2 protein lacking 232 amino acids of the C-terminal part of the protein. At the age of 2 years, the boy was referred because of development delay and movement disorder. He had mild mental retardation, cerebellar ataxia, nonepileptic myoclonic jerks of the neck and limbs, and mild kyphoscoliosis. There was no amino aciduria or metabolic acidosis. The patient excreted 61.6 g/l of glucose in the presence of normal blood glucose levels. Van den Heuvel et al. (2002) stated that they had no explanation for the neurologic symptoms in their proband. They could, however, exclude a defect in the transport of glucose into the brain because of normal glucose concentration in the cerebrospinal fluid. Glucose is transported into the brain by facilitated diffusion. Two types of glucose transporters, GLUT1 (138140) and GLUT3 (138170), are localized in the membranes of brain endothelial cells and are distinct from SGLT2.
