This article is from the Epilepsy FAQ, by Andrew Patrick (andrew@calvin.dgbt.doc.ca) with numerous contributions by others.
Seizures can affect intelligence, so prompt diagnosis and rapid control
of seizures is important. There is also a risk if seizures are
prolonged and there is a significant reduction in oxygen in the brain
during seizures. However, these are extremely rare occurrences. In the
case of developmentally delayed persons with Epilepsy, it is most
likely that the cause of the developmental delay is also the cause of
the seizures. In most cases, people with Epilepsy have normal
intelligence.
 
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