Additional studies examined if the enhanced risk for alcohol problems observed in children of parents with AUD remained even if the offspring had been separated from that parent early in life. In 1972, analyses of half-siblings from AUD families and control families found that adverse alcohol outcomes in offspring related more closely to presence of an AUD in a biological parent than to alcohol problems in a non-biological parent who raised the child.6 These data were consistent with subsequent larger and better controlled investigations of adoptees in Scandinavia.2,7 Overall, these studies supported the conclusion that genes and gene-environment interactions explained between 40% and 60% of the AUD risk.8–10
