Table 2.

Use of the Children-of-Twins Design to Separate Genetic and Environmental Influences on Risk of Psychopathology in the Children of Alcohol-Dependent Parents

		Level of Risk to Children Due to:
Parent's History of Alcohol Dependence	Alcohol Dependence History of the Parent's Twin	Genetic Effects	Familial Environmental Effectsa	Genotype × Environment Interaction Effects
Alcohol dependent	Any	High	High	High
Nondependent	Alcohol dependent, identical twin	High	Low	Low
Nondependent	Alcohol dependent, fraternal twin	Intermediate	Low	Low
Nondependent	Nondependent	Low	Low	Very Low

^aincluding other shared environmental effects associated with parental alcohol dependence.

NOTE: Predictions assume statistical control for psychopathology in the partners of the twins (i.e., the biological co-parents of their children), and for psychiatric comorbidity in the twin parents. SOURCE: Jacob et al. 2001.