The validity of our findings is also supported by the work of many previous researchers who have identified the contribution of GABA and glutamate receptors to AD 19. Some of the genes contained in the gene sets tested here have been previously tested as candidate genes albeit with inconsistent results. Some of the others have yet to reveal association with AD; however since the effect sizes are small, they would not likely have yielded association when tested individually, even if the association is real. For example, previous studies have shown that a number of individual genes for components of the GABAA receptor are associated with AD. Investigations in the COGA sample showed that variations in GABRA2 were highly associated with AD as well as the beta frequency of the electroencephalogram 20. Another study 21 produced evidence showing gene-environment correlation and interaction in the impact of GABRA2 variants and risk for AD. Other studies have reported association between AD and GABRA6 22–24, GABRB3 and severe alcoholism 25 and Song et al 24 found evidence of association with GABRA5 and GABRB3. The
