Together, results are highly suggestive of genetic but not environmental transmission of risk from parental AUD for externalizing and total problem behaviors, but there are several limitations of the present study to warrant cautious interpretation. First, the sample was drawn from predominantly Causation twin panels in Australia. Given reported differences by race in risk of alcohol use and disorder (Grant, 1997; Hasin, Stinson, & Grant, 2007), it is possible that observed patterns differ for other racial or ethnic groups. Observed patterns might also differ cross-nationally, further restricting generalizability. Another limitation pertains to sample ascertainment, with well-educated individuals over-represented in both panels (see Heath et al., 2001; Heath, Madden, & Martin, 1998).
