Occurrence of GLUT1 deficiency syndrome in patients treated with ketogenic diet.

Glucose transporter 1 deficiency syndrome (GLUT1-DS) is a treatable metabolic encephalopathy caused by a mutation in the SLC2A1 gene. This mutation causes a compromised transport of glucose across the blood-brain barrier. The treatment of choice is ketogenic diet, with which most patients become seizure-free. At the National Centre for Epilepsy, we have, since 2005, offered treatment with ketogenic diet (KD) and modified Atkins diet (MAD) to children with difficult-to-treat epilepsy. As we believe many children with GLUT1-DS are unrecognized, the aim of this study was to search for patients with GLUT1-DS among those who had been responders (>50% reduction in seizure frequency) to KD or MAD. Of the 130 children included, 58 (44%) were defined as responders. Among these, 11 were already diagnosed with GLUT1-DS. No mutations in the SLC2A1 gene were detected in the remaining patients. However, the clinical features of these patients differed considerably from the patients diagnosed with GLUT1-DS. While 9 out of 10 patients with GLUT1-DS became seizure-free with dietary treatment, only 3 out of the 33 remaining patients were seizure-free with KD or MAD treatment. We therefore conclude that a seizure reduction of >50% following dietary treatment is not a suitable criterion for identifying patients with GLUT1-DS, as these patients generally achieve complete seizure freedom shortly after diet initiation.