Glucose transporter protein type 1 deficiency syndrome is a metabolic disorder manifesting as cognitive impairment, acquired microcephaly, epilepsy, and/or movement disorder caused by mutations in the SLC2A1 gene. We describe a cohort of isolated and familial cases of glucose transporter protein type 1 deficiency syndrome, emphasizing seizure semiology, electroencephalographic (EEG) features, treatment response and mutation pathogenicity. SLC2A1 mutations were detected in 3 sporadic and 4 familial cases. In addition, mutations were identified in 9 clinically unaffected family members in 2 families. The phenotypic spectrum of glucose transporter protein type 1 deficiency is wider than previously recognized, with considerable intra-familial variation. Diagnosis requires either hypoglycorrachia followed by SLC2A1 sequencing or direct gene sequencing. A ketogenic diet should be the first line of treatment, but more flexible diets, like the Atkins modified diet, can also be followed. Carbonic anhydrase inhibitors, such as acetazolamide or zonisamide, can be effective for seizure control.

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