The fraction of variance accounted for by the subset of SNPs in the GABA receptor genes selected was 3.8 %, while the fraction of variance accounted for by the subset of SNPs in the six selected glutamate receptor genes was 3.3 %. We note that these estimates are comparable to previously published estimates for the contributions of multiple variants in distinct neurotransmitter systems to a different psychiatric phenotype (ADHD) 50. For comparison purposes, the fraction of variance that would be explained by comparably sized subsets of SNPs, randomly selected from those of comparable minor allele frequencies, would be 1.1% and 0.6% respectively. We think that a systematic search of other gene sets (including those related to metabolism of alcohol and taste) along the lines performed here may yield further useful results.
