A 13.5 year old Turkish girl (fig. 1) presented at the emergency department in generalised status epilepticus which responded promptly to intravenous phenytoin. Her family history was uniformative and there was apparently no consanguinity of the parents. The patient was reported as being always a little “slower” for her age, without causing special concern. An EEG performed 12 hours after termination of the status epilepticus, demonstrated non-specific generalized slowing. Two days after neurological examination revealed mild mental retardation, mild macrocephaly (97th centile), head tremor, mild dysdiadochokinesia and a slightly ataxic gait with profound difficulties in tandem gait. CT of the brain revealed hypodensities of the subcortical white matter (fig. 2). MRI demonstrated an increased signal of the subcortical white matter (adjacent to the U-fibers) at the T2-weighted sequences (fig. 3). One year after the initial presentation the patient is still free of seizures on phenytoin therapy, with no evidence of further deterioration of her psychomotor development.