The OZ-ALC sample consisted of 6169 individuals (for this study, 5816 regular drinkers were included) from 2356 families ascertained from 3 coordinated studies derived from a larger Australian twin registry: (i) the Nicotine Addiction Genetics (NAG) Study which ascertained heavy smoking index cases; (ii) the OZ-ALC-EDAC study, which ascertained index cases with a history of alcohol dependence or scoring above the 85th centile for heaviness of drinking factor score (operationalized as in the study by Grant et al.22); (iii) the OZ-ALC-BIGSIB study, which ascertained large sibships (4–14 full siblings), regardless of sibling phenotypes. Further details regarding recruitment may be found in the study by Heath et al.18 OZ-ALC was not ascertained for alcohol dependence (although some contributing studies were ascertained for heavy smoking and heavy alcohol consumption) and includes 1714 alcohol-dependent individuals (mean age of onset 26.3 years).
