One variant of substance-use disorder is characterized by behavioral disinhibition. In this report, we martial evidence for a model for the development of this variant. We hypothesize that genetic liability for this variant is reflected in a spectrum of risk indicators linked to the inability or unwillingness to inhibit behavioral impulses. Included in this spectrum are personality traits suggesting low constraint, and externalizing psychopathology, including conduct, oppositional defiant, and attention-deficit disorder in children and antisocial personality disorder and behavior in adults. We further hypothesize that these individual differences in behavioral disinhibition are manifestations of underlying central nervous system processes associated with various psychophysiological anomalies, some of which may index genetic risk for substance abuse. Support for the model is derived from the analysis of findings from the Minnesota Twin Family Study, an epidemiological investigation of approximately 2,700 adolescent twins and their parents.

Hyperactivity/impulsivity predicts later substance problems, even after growth in later-emerging CD is considered, whereas inattention alone poses less risk. Even a single symptom of ADHD or CD is associated with increased risk. Failure in previous research to consistently observe relationships between ADHD and substance use and abuse outcomes could be due to reliance on less-sensitive categorical diagnoses.

A self-report measure of conflict and aspects of warmth in the parent-child relationship was completed by 1,330 11-year-old twins, 1,176 of whom completed the inventory again 3 years later. On average, adolescents' perceptions of the quality of the parent-child relationship declined consistently and moderately between age 11 and age 14. Conflict with parents increased, whereas all aspects of warmth decreased; changes were significantly greater for girls than boys. Variances increased with age, primarily because of increases in the magnitude of genetic effects. Heritability estimates ranged from .09 to .31 at intake and .35 to .45 at follow-up and tended to be higher for boys than girls. Changes in the parent-child relationship are interpreted as reflecting genotype-environment correlation processes whereby adolescents increasingly influence their relationships with their parents.

This study found no significant gender differences in the effects of ADHD and conduct disorder on substance use and abuse, although there was some suggestion that girls with ADHD might be at slightly higher risk than boys for substance abuse. In addition, increased risk of substance abuse among adolescents with conduct disorder may be primarily confined to those with persistent conduct disorder.

Our findings indicated that AFD is not specifically associated with alcoholism but rather is correlated with a broad range of indicators of disinhibited behavior and psychopathology. Moreover, individuals who first drink at a relatively early age manifest elevated rates of disinhibitory behavior and psychopathology before they first try alcohol. Taken together, these findings suggest that the association of AFD with alcoholism reflects, at least in part, a common underlying vulnerability to disinhibitory behavior. Whether an early AFD directly influences risk of adult alcoholism remains unclear.