Gene–Environment Interplay in Adolescent Drinking Behavior Richard J. Rose, Ph.D., and Danielle M. Dick, Ph.D. Many people begin to consume alcohol and establish drinking patterns during adolescence, making this an important developmental period for alcohol researchers to study. Both drinking initiation and establishment of drinking patterns are influenced to varying degrees by genetic as well as environmental factors. Using twin studies conducted in Finland and other countries, researchers have analyzed the specific genetic and environmental influences as well as the gene–environment interactions that shape drinking behavior in adolescence. These studies indicate that drinking initiation is determined primarily by environmental influences, whereas the establishment of drinking patterns is determined mostly by genetic factors, which themselves are subject to moderation by the environment. KEY WORDS: adolescent; young adult; age of onset; AOD (alcohol and other drug) use initiation; AOD use pattern; genetic theory of AODU (alcohol and other drug use); hereditary factors; environmental factors; hereditary vs. environmental factors; social environmental risk and protective factors; family risk and protective factors; longitudinal study; twin study; monozygotic twin; dizygotic twin; the FinnTwin studies; Finland; Collaborative Study on the Genetics of Alcoholism (COGA) he years between early adolescence it also is necessary to study the factors also exists in people without a family and young adulthood are a cru­ influencing drinking initiation. history. Tcial period for alcohol researchers Another reason to focus on early But what is the relevance of this to study, because drinking typically is adolescent drinking comes from research association? In most cases, it is hazardous initiated during adolescence, and by evidence indicating that people who to draw a causal connection based on young adulthood, individual differences begin drinking at an earlier age have a such observations. Thus, it is possible in established drinking patterns are evi­ heightened risk for negative consequences dent. The earliest stages of alcohol use of drinking, such as alcohol abuse or RICHARD J. ROSE, PH.D., is a professor merit particular attention because alcohol dependence. For example, emeritus in the Department of Psychology, research has suggested that the initia­ interviews of adults consistently and Indiana University, Bloomington, Indiana. tion of alcohol use must be distin­ convincingly have shown a strong asso­ guished from the frequency, quantity, ciation between an early initiation of DANIELLE M. DICK, PH.D., is an assistant and density (i.e., the number of drinks drinking and later alcohol­related prob­ professor in the Departments of consumed in a certain length of time) lems: People who report drinking as Psychiatry and Psychology, Washington of alcohol use once drinking is initiated. early as age 13 or 14 are much more University, St. Louis, Missouri. Consequently, analyses in adults with likely to exhibit alcohol­related behavior already established drinking patterns can problems in adulthood than people who The FinnTwin studies are supported by explain only part of the mechanisms began drinking at a later age (Grant National Institute on Alcohol Abuse and and contributing factors underlying and Dawson 1997). The association of Alcoholism grants AA–00145, AA–08315, the development of alcohol abuse and drinking problems with earlier age of AA–09203, and AA–12502; by the dependence. To obtain a more compre­ initiation is particularly strong in people Academy of Finland; and by the Yrjö hensive explanation of these processes, with a family history of alcoholism, but Jahnsson Foundation. 222 Alcohol Research & Health Gene–Environment Interplay in Adolescent Drinking Behavior that drinking initiation at an earlier age which the people live—that is, there interplay across development for a vari­ is causally related to greater vulnerabil­ are gene–environment interactions. ety of behaviors. Therefore, these ity to alcohol’s cumulative effects. A person’s susceptibility to develop­ research designs also are particularly Alternatively, early onset of drinking and ing alcohol dependence and other alcohol­ useful in understanding the develop­ a greater likelihood of later problems related problems manifests as an unfold­ ment of drinking behaviors. The most may simply be correlated—that is, they ing developmental process that involves widely used design is a longitudinal/ are independent signs or symptoms of both genetic and environmental factors developmental study of child or adoles­ people who are at elevated risk of alco­ and is continuously modulated by gene– cent twins and their parents. Several hol dependence. In the latter case, pre­ environment interplay. This concept research groups in the United States vention efforts designed to promote of a complex developmental process is and other countries are engaged in delays in age of drinking initiation supported by fundamental findings in developmental behavior­genetic research would do little to reduce the prevalence recent behavior­genetic research that of this kind, and many of these groups of adult alcoholism—an issue that is have profoundly altered the earlier view explore risk factors for alcoholism as important to resolve. One approach to that people are passive players who part of their research aims. This article doing this is to conduct longitudinal mechanically mirror their environmental focuses on two longitudinal studies of studies that follow, over several years, experience. Instead, recent research young Finnish twins and their parents genetically informative samples, such findings indicate the existence of exten­ known as the FinnTwin studies. as samples of twins who differ in their sive gene–environment correlations, Finland is particularly suitable for age at onset of drinking. whereby people are active agents who conducting longitudinal twin studies This article reviews recent findings help create the experiences to which because of the availability of compre­ from two ongoing longitudinal twin they are exposed, selectively seek envi­ hensive birth records, the ease of locat­ studies conducted in Finland that elu­ ronments to match their specific dispo­ ing twins as they grow up, and the high cidate the contributions of genetic and sitions, and modify their environments level of compliance of organizations environmental influences to initiation through their actions. In short, new and individuals with research requests. of drinking and later trajectories of research suggests that constant gene­by­ To acquire a large sample of twins that is representative of the entire pop­ alcohol use and abuse. Data from these environment interplay is involved in the development of alcoholism risk ulation, it is almost imperative that population­based FinnTwin studies help over time. investigators have access to a compre­ investigators address questions about To understand the factors affecting hensive birth registry for the region or factors contributing to various stages of the development of alcoholism, it is country under investigation. However, alcohol use. The resulting research has essential to appreciate this continuing many countries, including the United underscored the importance of the interaction of genetic and environmen­ States, do not have such registries. concept of dynamic gene–environment tal influences (e.g., how a child’s behav­ Some researchers in the United States interactions. ioral dispositions interact with that have attempted to obtain comprehen­ child’s household environment). Simi­ sive data sets by identifying all twin larly, it is important to acknowledge students enrolled in a large public The General Role of Genetic that the household environment does school system or by systematically and Environmental Factors not stand alone, but is “nested” within accessing birth records within a State in Alcohol­Related neighborhoods, schools, communities, and then searching for the current Behavior and cultures. Accordingly, the ways addresses of the twins so identified. in which a child expresses his or her In the Nordic countries, in contrast, Both genetic and environmental factors internal dispositions are modulated by the entire population is enrolled at contribute to the different stages in a the adult models, parenting practices, birth into a centralized population reg­ person’s drinking history. The factors peer interactions, access to alcohol, istry. In Finland, every newborn citizen that influence individual differences in and school and neighborhood environ­ is given a unique personal identifica­ whether, and at what age, drinking is ments to which the child is exposed. tion number that includes the person’s initiated are different in kind from the All of these factors either enhance or date of birth and a link to the biologi­ factors that influence individual varia­ reduce the risk for alcoholism that cal mother. Accordingly, researchers tions in patterns of drinking, once the results from the child’s genetic makeup. who have approval to access the registry acute subjective effects of alcohol inges­ can identify all people born on the tion are experienced. Moreover, it is same day to the same mother, thereby clear from numerous studies that The FINNTWINStudies identifying the nation’s entire popula­ although genetic factors have some tion of twins and other multiples. influence on drinking behavior, the Longitudinal studies using genetically Moreover,