Drinking or abstaining at age 14? A genetic epidemiological study

Background: Regular drinking by age 14 years is a significant risk factor f or alcoholism. and genetically informative data suggest that whether a youn g adolescent abstains or drinks is largely attributable to familial (or oth er shared) environmental factors. Methods: Three consecutive birth cohorts of Finnish twins, enrolled into a longitudinal study at age I I to 12 years, completed a follow-up questionna ire within 3 months of their 14th birthdays. The sample included 1380 twin sisters and 1330 twin brothers at age 14, and at that age, 35.4% reported u sing alcohol. Genetic analyses (model-fitting of twin pair data) and epidem iological analyses (logistical regressions of data from individual twins) w ere conducted to examine predictive factors of drinking versus abstinence a t age 14. Results: Polychoric correlations were substantial across all same-sex twin pairs but were lower for brother-sister twins, suggesting significant influ ences of common environments, with some sex-specific effects. Common enviro nmental effects were equivalent in male and female adolescents and accounte d for 76% of the total variation in abstinence/drinking. Logistical regress ion analyses among 2206 individual twins with complete data on risk-relevan t measures at both baseline and follow-up identified significant predictors of drinking or abstaining at age 14, including female sex, twin sibling of the opposite sex. accelerated pubertal development, and the twins' assessm ents, made at age 12, of reduced parental monitoring and a less supportive home atmosphere; drinking at age 14 was also predicted by behaviors rated b y the twins' classroom teachers 2 years earlier, increasing with rated beha vioral problems but decreasing with rated emotional problems. Conclusions: Our results show that environmental factors shared by twin sib lings account for most of the variance in abstaining or drinking at age 14. We identify predictors of drinking in the adolescent twins' home environme nts and in their dispositional behaviors. sibling interactions, and puberta l timing.