Timing of first alcohol use and alcohol dependence: evidence of common genetic influences

Abstract

Aims To estimate the magnitude of genetic and environmental influences on timing of first alcohol use and alcohol dependence (AD) and to quantify the overlap in these influences across the two alcohol-related outcomes. Participants The sample consisted of 5,382 twins (2,691 complete pairs), aged 24 to 36 years, from the Australian Twin Registry. Measurements History of alcohol use and DSM-IV alcohol dependence were assessed by structured telephone interview. Findings In both sexes, the relationship between age at first alcohol use and risk for AD followed a linear trend, such that the highest rates of AD were observed in individuals who began drinking at an earlier than average age (14 years or younger). Heritability estimates for timing of first alcohol use and AD were 36% and 53%, respectively. Shared environmental factors accounted for 15% of variance in initiation. There was no evidence of shared environmental influences on AD. The genetic correlation between timing of first alcohol use and AD was 0.59. Conclusions Findings highlight the substantial role of genetics in the development of AD and the early manifestation of that genetic risk in the timing of alcohol use initiation, which, unlike AD, is also influenced to a modest degree by shared environmental factors. The considerable overlap in heritable influences – and the virtual absence of overlap in individual-specific environmental influences – on initiation of alcohol use and AD indicates that the association between age at first drink and AD is attributable in large part to common genetic sources of variance.

Causal Influence of Age at First Drink on Alcohol Involvement in Adulthood and Its Moderation by Familial Context

“…This fi nding indicates that the unique environment plays a smaller role in predicting adult drinking frequency than family context (genes and/or shared environment). This supports previous studies (e.g., Agrawal et al, 2009;Sartor et al, 2009) documenting that family context effects are the main predictors for alcohol disorders. This hypothesis was not supported for drinking quantity, however, indicating that unique environment and family context effects were of similar magnitude in predicting adult alcohol quantity.…”

“…There was also a signifi cant between-twin-pair (i.e., familial context) effect of drinking onset on both drinking frequency and quantity. Previous studies have documented that the relationship between age at onset and lifetime alcohol use disorder diagnoses can be attributed mainly to genetic and shared environmental infl uences rather than unique environmental infl uences (e.g., Agrawal et al, 2009;Fowler et al, 2007;Sartor et al, 2009). By contrast, both unique environmental and familial context effects seem to be predictors of adult alcohol involvement.…”

“…Following from Agrawal et al (2009), responses were censored such that individuals reporting ages below fi ve were equated to fi ve. Age at onset was treated as a continuous variable (as opposed to a binary variable as in some previous studies [e.g., Grant et al, 2006;Sartor et al, 2009]). This was done to better suit a multilevel modeling framework and to capture nuances within discordance.…”

“…In a twin design, any latent unmeasured risk factors that are attributable to correlated sets of genetic or shared environmental risk factors can be controlled. Some twin studies found that the relation between early drinking onset and later lifetime alcohol dependence can be primarily attributed to shared genetic risk factors and not to unique environmental infl uences (Agrawal et al, 2009;Prescott and Kendler, 1999;Sartor et al, 2009). However, other twin studies report modest individual-specifi c environmental infl uences shared between early drinking and later problematic use (Fowler et al, 2007;Grant et al, 2006).…”

Associations Between ADH Gene Variants and Alcohol Phenotypes in Dutch Adults

“…Additive genetic influences explain between 30% and 54% of the variation in alcohol consumption among adults (Hansell et al, 2008;Kendler et al, 2008;Whitfield et al, 2004). Heritability estimates for the risk of alcoholism or abuse in adults range from 30% to 75% (Heath et al, 1997;Jang et al, 2000;Kendler et al, 1997;Knopik et al, 2004;Prescott et al, 1999;Sartor et al, 2009;Walters, 2002;Xian et al, 2008). Estimates of genetic influences on alcohol initiation are more variable.…”