The lack of concordance across GWASs could be partially due to different measures of alcohol consumption used in different study populations or even across different samples from the same population. Common measures of alcohol consumption are frequency of drinking (weekly and annually), quantity by frequency, maximum drinks in a 24 hour period, frequency of heavy drinking and frequency of intoxication [5]; if these measures are not perfectly correlated, they will be associated with different SNPs. Association studies in humans are limited in resolution by the structure of LD; to the extent that LD varies among populations, different genes may be implicated in different studies. Moreover, rare alleles that contribute to variation in alcohol consumption are essentially blind to detection by association studies using common variants, and many SNPs with small effects may contribute to risk for alcohol dependence.
