BACKGROUND: Glucose transporter type 1 deficiency syndrome (Glut1-DS) is a metabolic epileptic encephalopathy caused by defects in the cerebral glucose transporter GLUT1. It is characterized by infantile seizures refractory to anticonvulsants, deceleration of head growth, and delays in mental and motor development. Low brain glucose and subsequent energy deficiency is considered the major pathogenic factor causing seizures. The ketogenic diet (KD) is the only causal treatment available for Glut1-DS, and its therapeutic effect resides in its ability to provide an alternate source of energy for the brain. However, seizure control with KD is not complete in many patients and the long-term cognitive outcome is not optimal. Biochemically, these observations can be explained by a lack of energy for metabolic functions provided by pathways derived exclusively from glucose, which the alternate energy from the KD fails to supplement.