One of the relatively few published studies utilizing this design reported that, while offspring of MZ and DZ twins with a history of alcohol dependence were significantly more likely to exhibit alcohol abuse/ dependence than were offspring of nonalcoholic fathers, offspring of an unaffected (i.e., no history of abuse or dependence) MZ twin whose co-twin had alcohol dependence were no more likely to exhibit alcohol abuse or dependence than were offspring of nonalcoholic twins whose co-twin was also unaffected. This pattern of results suggests that a low risk environment (no exposure to paternal alcohol dependence) can ameliorate the influence of high risk genetic background.28
