Üstyol A, Takahashi S, Hatipoğlu HU, Duman MA, Elevli M, Selçuk Duru HN. A novel mutation in SLC2A1 gene causing GLUT-1 deficiency syndrome in a young adult patient. Turk J Pediatr 2019; 61: 946-948. GLUT-1 deficiency syndrome is a rare, frequently unrecognized metabolic encephalopathy that is probably underdiagnosed. Although developmental delay, acquired microcephaly, spasticity, and impaired coordination were initially described as the classic findings, mild cases with no pronounced neuromotor compromise have since been included in the broad clinical spectrum with new mutations being identified more recently. We report a case of myoclonic seizures not responding to anti-epileptics since the age of one year in a 17-year-old patient with a normal phenotype and neuromotor development. Previously unreported p.Phe389Leu mutation was determined in the SLC2A1 gene in our patient. This case will be useful in clarifying the phenotype of GLUT-1 deficiency and reveals a new pathogenic mutation.