use based on the Genome-wide Complex Trait Analysis65 software package. Verweij et al.26 estimated that 6% of the variance in lifetime cannabis use is explained by aggregated common SNPs (MAF>0.05). Minică et al.27 found an estimate of 25%. Provided that the current sample is much larger than the samples used in the previous studies, we conclude that approximately one-third to half of the heritability is explained by common SNPs captured on a GWAS array. Other sources of variation may explain the discrepancy between SNP- and twin-based heritability estimates. For example, age-related genetic differences, non-additive genetic variance, interactions between genetic variants and environmental risk factors, epistasis and/or rare mutations may also have a role.
