Some studies have demonstrated that cognitive decline occurs in Dravet syndrome, starting shortly after the onset of seizures, rapidly progressing and then plateauing within a few years. It is unclear whether children that develop the syndrome had entirely normal cognitive skills before seizure onset, since subtle impairment easily escapes recognition in small infants. It is also difficult to demonstrate whether a recognisable profile of cognitive impairment or a definite behavioural phenotype exists. No clear-cut imaging or neuropathological marker or substrate has been recognised for cognitive impairment in this syndrome. However, there are different potentially causative factors, including the specific effects on the Nav1.1 channels caused by the underlying genic or genomic defect; frequent and prolonged convulsive and non-convulsive seizures or status epilepticus; recurrent subtle ictal phenomena, such as that accompanying pronounced visual sensitivity; the use of antiepileptic drugs with cognitive side effects, especially in heavy multiple-drug therapy; and the restrictions that children with severe epilepsy inevitably undergo.