Parental OPD also significantly predicted offspring AUD in our sample. This relationship was mainly attributable to a contribution from the mother, as the rates of OPD in fathers without AUD were very low. These results suggest that familial contributions toward offspring risk of alcoholism may not be limited to familial alcoholism, but may also be the result of other psychiatric illness in the family. It is possible that the effect of parental OPD is mediated through an effect on risk of offspring mental disorders associated with increased risk of AUD. Such disorders may not only include attention deficit hyperactivity disorder (Knopik et al., 2009) and conduct disorder (Haber al., 2005), but also depression and anxiety disorders (Flensborg-Madsen et al., 2009). Support for this interpretation was obtained in an analysis that included offspring OPD as predictor. Offspring OPD was associated with an odds ratio of 13, and the effects of parental OPD became nonsignificant, while the effects of parental AUD remained significant. It is also possible that alcoholism played a role in some hospital admissions of parental OPD without being reflected
