Glucose is the main energy source for the brain; therefore, diseases that cause hypoglycemia (e.g., fatty acid oxidation defects) or impair brain glucose transport [e.g., glucose transporter type 1 (GLUT-1) deficiency] can cause brain energy deficiency leading to seizures. The gene discussed is SLC2A1; the disease is hyperinsulinemic hypoglycemia, familial, 4.