GLUT1 Deficiency Syndrome

A 18-month-old boy presents with recurrent seizures characterized by generalized 2.5–4 Hz spike-wave discharges on EEG, as shown by the pattern marked **A** in the diagram. The seizures are notably worse before meals and improve dramatically after feeding. CSF glucose is found to be 35 mg/dL with a CSF:serum glucose ratio of 0.38, while serum glucose is normal at 95 mg/dL. CSF lactate is normal. Which of the following is the most likely diagnosis?

A 4-year-old girl with medication-refractory epilepsy presents with absence-like staring spells and myoclonic jerks that worsen before meals and improve after eating. MRI brain is normal. EEG performed during fasting shows the pattern marked **A** in the diagram (generalized 2.5–4 Hz spike-wave discharges), but remarkably improves after a carbohydrate-rich meal. Lumbar puncture during fasting reveals CSF glucose 28 mg/dL with simultaneous serum glucose 90 mg/dL (CSF/serum ratio 0.31; normal >0.6). Genetic testing confirms a heterozygous SLC2A1 mutation. Which of the following BEST explains the postprandial EEG improvement and is the cornerstone of long-term management in this condition?