This finding needs emphasizing since it contradicts the results of a meta-analysis of the effect of a functional Val158Met (rs4680) polymorphism in catechol-O-methyltransferase (COMT) on neural endophenotypes [16]. That paper tested the hypothesis that “neural intermediate phenotypes are indeed more penetrant than behavioral ones” and reported a significant association between the COMT variant and test of ‘prefrontal activation’. The size of the effect was Cohen's d = 0.73. For those not familiar with this measure of effect size, it is the approximately the same as 12% of the variance, much larger than that found in the GWAS mentioned above.
