Energy deficiency can cause seizures in various metabolic disorders including mitochondrial diseases, glucose transporter type 1 (GLUT-1) deficiency, guanidinoacetate methyltransferase (GAMT) deficiency, and disorders causing hypoglycemia including fatty acid oxidation defects, disorders of gluconeogenesis, and glycogen storage disorders (Table 1). The gene discussed is SLC2A1; the disease is mitochondrial disease.