T he Minnesota Twin Family Study is a longitudinal study of 11-year-old and 17-year-old twins and their parents designed to examine factors related to the etiology of substance abuse and related problems. At study intake, the twins and their parents participate in a day-long assessment in our laboratory that includes measures of endophenotypes (e.g., event-related potentials, EEG, autonomic nervous system reactivity, startle eye-blink), psychopathology, personality, cognitive ability, anthropometry, and environmental risk/protective factors. DNA derived from blood is also collected. A parallel longitudinal study of adolescent adoptive siblings, biologically related siblings, and their parents is also underway. Over 1500 twin families and 350 adoptive and biological sibling families have already entered the longitudinal phase of the study. This article provides an overview of study methods, highlights published findings, and describes procedures in place to foster collaboration with other investigators.Originating over 10 years ago, the Minnesota Twin Family Study (MTFS) is an ongoing population-based, longitudinal investigation of same-sex twin children and their parents that examines the etiology of substance use disorders from a developmental, behavior genetic perspective. Much of the focus of the MTFS is on the notion that an inherited predisposition to develop these disorders is expressed in early adolescence through undersocialized or disinhibited behavior. We further hypothesize that this predisposition is manifest in psychophysiological markers derived from tasks that tap individual differences in inhibitory control. A comprehensive overview of the project along with a summary of early findings can be found in Iacono et al. (1999).
Twin RecruitmentTwo age cohorts are included, preadolescent twins recruited at approximately age 11, when they are in grades 5 or 6, and late adolescent twins, recruited at approximately age 17, during their last year in secondary school. Because we rely on publicly available Minnesota birth certificates to identify twins, only those born in Minnesota were eligible for study inclusion. This statewide sample is broadly representative of the Minnesota population. About 60% of the sample come from the seven counties that compose the Minneapolis-St. Paul urban area. The remainder live in smaller cities, towns and rural areas throughout the state and in towns in neighboring states that border Minnesota. Reflecting the ethnic composition of the state at the time they were born, almost all the twins are Caucasian (over 95%), with the majority having German and Scandinavian ancestry.At study intake, the twins, together with their parents, travel from around the state to spend a day in our university laboratory. The day is split between interviews with all four family members and time in the psychophysiology laboratory. This procedure, with some variations, is repeated every three to four years. Because the first twins were assessed in 1991, some of the twins who were 11 at study intake...