In the present study, the explained variance in the regression analyses varied from 0.4% for glasses alcohol per week up to 1.5% for age at regular drinking. Other studies reported explained variances varying from 0,1 to 3%.(32,48–50). Even when taking all available SNPs into account, the explained variance is lower than the heritability estimates from twin studies (26,30). An explanation for this ‘missing heritability’ problem is that the mutations causing variation in a trait are not in perfect linkage disequilibrium with any of the measured SNPs and therefore part of the genetic variance is undetected by the SNPs. The causal variants are expected to have lower minor allele frequencies (<0.1) because they are more likely to be subject to some form of natural selection that leads to variants negatively associated with reproductive fitness (51).
