The Epilepsy Genetic Association Database (epiGAD): analysis of 165 genetic association studies, 1996-2008.

We have created the Epilepsy Genetic Association Database (epiGAD, http://www.epigad.org, an online database of epilepsy genetic association studies. A systematic search using several search engines identified 165 studies. Herein we analyze the types of studies available, the sample sizes used, and the strength of the findings. Common questions examined were susceptibility to idiopathic generalized epilepsy, focal epilepsy, or febrile seizures, and pharmacogenomic approaches to drug-resistant epilepsy. Sample sizes were generally small; 80% of studies had 200 or fewer cases, although more recent studies published from 2005-2008 incorporated slightly larger sample sizes. No association was judged as "strong" using current criteria for assessing genetic associations--this is probably due to inadequate sample sizes. Sample sizes need to increase, either by research collaboration or via systematic reviews and meta-analyses. We believe epiGAD will facilitate future meta-analyses.