families where ALDH2*2 carrying offspring are raised by ALDH2*2 carrying biological parents, the protective effect associated with the ALDH2*2 allele is likely to be amplified, because it will also include the environmentally-mediated influence of parental ALDH2*2 genotypes (although it has not yet been demonstrated that this gene-environment correlation actually exists). In our sample, where white adoptive parents do not carry the ALDH2*2 allele, differences in alcohol use associated with participants’ ALDH2 genotype should be exclusively a function of that genotype, and will not be confounded with parental ALDH2 genotype. Similarly, although a large proportion of the elder siblings of genotyped target participants were themselves of Korean descent, they were not biological siblings to the target participants, so the environmental effect of elder sibling drinking was not confounded by a systematic relationship between target participant and elder sibling ALDH2 genotypes.
