Minnesota Twin Family Study

The Study  An ongoing population-based, investigation of same-sex twin children and their parents that examines the origination of substance use disorders from a developmental, behavior genetic perspective.  Hypothesis: an inherited predisposition to develop these disorders is expressed in early adolescence through under- socialized or dis-inhibited behavior.

Assessments  Focus on four areas: Academic ability, personality, and interests, Family and social relationships, Mental and physical health, and Physiological measurements.

Twin Males & Females  Findings: Children who developed adult symptoms of antisocial personality disorder between the ages of 15 and 17 were about three times more likely to develop a substance use disorder by age 17 than youths with conduct disorder who did not develop adult symptoms.

Twin Males  Findings: 11-year-old boys who engaged in delinquent behavior by age 11 were more likely than those who developed delinquency later and those who were non- delinquent to develop substance dependence symptoms over a 6-year period.

Fathers of Male Twins  Findings: Fathers with more severe and persistent antisocial behavior had a greater likelihood of developing a substance use disorder, and a greater likelihood of having antisocial sons.

IQ Scores  The Minnesota Twin study found a positive correlation of +.71 between the IQ scores of identical twins.  This means that if one of the twins has a high IQ, the other also seems to have a high IQ.

Other Twin Data Findings  Early alcohol use is heritable  Genetic factors underlying symptoms of psychopathology were found to contribute to risk of early alcohol abuse, and eventually leads to alcohol, especially in boys.

Conclusion  There exists an inherited predisposition for a spectrum of externalizing psychopathology that includes antisocial personality, alcoholism, and other substance use disorders.