Epilepsy and autism: is there a special relationship?

Abstract

Increasingly, there has been an interest in the association between epilepsy and autism. The high frequency of autism in some of the early-onset developmental encephalopathic epilepsies is frequently cited as evidence of the relationship between autism and epilepsy. While these specific forms of epilepsy carry a higher-than-expected risk of autism, most, if not all, of the association may be due to intellectual disability (ID). The high prevalence of interictal EEG discharges in children with autism is also cited as further evidence although errors in the diagnosis of epilepsy seem to account for at least part of those findings. The prevalence of ID is substantially elevated in children with either epilepsy or autism. In the absence of ID, there is little evidence of a substantial, if any, increased risk of autism in children with epilepsy. Further, although the reported prevalence of autism has increased over the last several years, much of this increase may be attributable to changes in diagnostic practices, conceptualization of autism in the presence of ID, and laws requiring provision of services for children with autism. In the context of these temporal trends, any further efforts to tease apart the relationships between epilepsy, ID, and autism will have to address head-on the accuracy of diagnosis of all three conditions before we can determine whether there is, indeed, a special relationship between autism and epilepsy.

Figure 1

Two hypotheses: (a) Intellectual disability is independently co-morbid with autism and with epilepsy thus inducing an apparent association (large overlap) between the latter two. Absent ID, the overlap between epilepsy and autism in the absence of intellectual disability is no greater than expected by chance alone. (b) Independent associations between epilepsy and ID, ASD and ID; ASD and epilepsy with some having all three disorders. The question on hand is whether the area indicated by the question mark (epilepsy with ASD in the absence if ID) occurs at a greater frequency than expected based on the prevalence of ASD in the general population without either ID and epilepsy and based on the prevalence of epilepsy in the population without either ID and ASD.