approximately one third of the variance in AD is shared with variance in initiation (Fowler et al., 2007; Prescott and Kendler, 1999) and a recent study of Australian twins reported a correlation of 0.59 between the heritable factors influencing age at initiation and those influencing AD (Sartor et al., 2009). Prescott and Kendler’s (1999) investigation of initiation of alcohol use and AD revealed that the association could be accounted for entirely by familial influences, nearly all genetic, but others have concluded that the association is not attributable in full to familial risk factors (Grant et al., 2006). The degree to which heritable influences on initiation and problem use can be traced to a common source determines the extent to which age at first drink can be treated as a marker for genetic liability to alcohol-related problems. Given the inconsistencies between African Americans and European Americans on lifetime use, age at first drink, rates of alcohol-related problems, and the association between early use and problem drinking, investigation of this question in a sample including both ethnic groups is warranted.
