In 1991, De Vivo et al. published a case report describing two patients presenting with developmental delay, seizures, and persistent hypoglycorrhia (reduced amounts of glucose in the cerebrospinal fluid). This clinical presentation was thought to be related to a lack of glucose entering the brain, caused by a genetic defect affecting the patients’ GLUT1 transporters. Both patients were treated with a ketogenic diet, resulting in a prompt end to the seizures. This case report constituted the first description of GLUT1 Deficiency Syndrome (GLUT1 DS). In 1998, mutations in genetic coding for the GLUT1 transporter were reported to be the molecular basis for disrupted glucose transport. Since 1991, more than 400 patients worldwide have been diagnosed with GLUT1 DS.