Abstracts

Rationale: In the absence of an identifiable structural lesion, epileptic myoclonus in infancy is associated with various genetic conditions, ranging from a benign genetic etiology to more severe genetic metabolic derangements with developmental delays. Here, we report 2 infants with glucose transporter 1 deficiency syndrome (GLUT1DS) that presented with epileptic myoclonus. One had an electroclinical phenotype compatible with benign myoclonic epilepsy of infancy (BMEI) and the other had opsoclonus and a robust response to steroids.Methods: Case 1: A 16-month old girl presented at 8 months of age with daily myoclonus. EEG studies confirmed its epileptic nature, and revealed a normal interictal background. Her development, neurological exam and head circumference were normal. Magnetic resonance imaging (MRI) of the brain was normal. Case 2: A 15-month old girl presented with opsoclonus at 1.5 months of age and subsequently developed global developmental delays and epileptic myoclonus at 4 months of age. She was normocephalic and her neurological exam revealed mild hypotonia. A brain MRI was normal. An EEG revealed multifocal spikes, a normal interictal background, and confirmed that the opsoclonus was not epileptic.Results: Case 1: On the basis of normal development and epileptic myoclonus upon on a normal interictal background, the infant was originally diagnosed with BMEI. She was treated with levetiracetam and had resolution of seizures. Further genetic testing however, revealed a previously described pathologic frameshift mutation in the SLC2A1 gene (del. C.505-507). She was diagnosed with GLUT1DS at 12 months of age, and was started on the ketogenic diet. She remains normocephalic and developmentally on track. Case 2: This infant’s myoclonus and opsoclonus responded to prednisone (40 mg daily), but recurred after weaning it at 7 months. The workup for neuroblastoma was negative. Cerebrospinal fluid studies revealed a glucose level of 37 mg/dL with a concurrent plasma glucose of 84 mg/dL. Subsequent genetic testing revealed a previously unreported heterozygous missense mutation in the SLC2A1 gene (c460G>A;p.Gly164Arg). She was diagnosed with GLUT1DS and started on the ketogenic diet at 8 months of age with complete resolution of the opsoclonus and myoclonus. She remains normocephalic, and her developmental milestone acquisition has accelerated.Conclusions: The cases presented here reveal that not only can GLUT1DS be at the origin of infantile epileptic myoclonus, but that the condition also has protean presentations that can mimic BMEI, and at times present with opsoclonus. Testing for GLUT1DS should be considered in infants who present with an electroclinical phenotype compatible with BMEI, as there is a strong need to initiate the ketogenic diet in a timely fashion to maximize the possibility of milestone acquisition and seizure freedom. We also propose that suspicion for GLUT1DS should be raised in infants with opsoclonus and epilepsy who respond to steroids and remain with an elusive pathology.