A statistical mediation model was developed within a twin design to investigate the etiology of alcohol use disorder (AUD). Unlike conventional statistical mediation models, this biometric mediation model can detect unobserved confounding. Using a sample of 1410 pairs of Norwegian twins, we investigated specific hypotheses that DSM-IV personality-disorder (PD) traits mediate effects of childhood stressful life events (SLEs) on AUD, and that adulthood SLEs mediate effects of PDs on AUD. Models including borderline PD traits indicated unobserved confounding in phenotypic path coefficients, whereas models including antisocial and impulsive traits did not. More than half of the observed effects of childhood SLEs on adulthood AUD were mediated by adulthood antisocial and impulsive traits. Effects of PD traits on AUD 5?10 years later were direct rather than mediated by adulthood SLEs. The results and the general approach contribute to triangulation of developmental origins for complex behavioral disorders.
The inheritance of alcoholism was studied in 862 Swedish men adopted by nonrelatives at an early age. Both the congenital and postnatal backgrounds of the adoptees modify their risk for alcohol abuse. We distinguish two forms of alcoholism that have distinct genetic and environmental causes and differ in their association with criminality, severity of alcohol abuse, and the frequency of expression in biological mothers. Postnatal milieu determines the frequency and severity of expression of the common type of susceptibility in both men and women. In contrast, the less common type is highly heritable in men but is seldom expressed in mothers of affected men.