The importance of genetic factors for alcohol-related phenotypes has been well-established through twin studies (Prescott and Kendler, 1999; Knopik et al., 2004) and more recently through genome-wide association studies (GWAS). For instance, twin studies have shown that additive genetic influences account for 18–30% of the variance in alcohol-related phenotypes (i.e., heavy episodic drinking) for young adult females and 39–57% for young adult males (King et al., 2005), while GWAS have identified several single nucleotide polymorphisms (SNPs) that may contribute to this variance, including those involved in the transcription of enzymes responsible for alcohol metabolism (Bierut et al., 2012; Gelernter et al., 2014). However, genetically associated markers identified through GWAS only account for a fraction of the total genetic variance. Using a method called genome-wide complex trait analysis (GCTA; Yang et al., 2011) and data from Netherlands Twin Register, one study estimated that the total variance explained by common SNPs for adult alcohol use problems was 33%, suggesting that a large portion of the heritability can be explained by variations in common SNPs in aggregate, rather than in isolation (Mbarek et
