Genetic and family and community environmental effects on drug abuse in adolescence: a Swedish national twin and sibling study

Abstract

Objective: Using Swedish nationwide registry data, the authors investigated genetic and environmental risk factors in the etiology of drug abuse by twin sibling modeling. The authors followed up with epidemiological analyses to identify shared environmental influences on drug abuse.

Method: Drug abuse was defined using public medical, legal, or pharmacy records. Twin and sibling pairs were obtained from the national twin and genealogical registers. Information about sibling pair residence within the same household, small residential area, or municipality was obtained from Statistics Sweden. The authors predicted concordance for drug abuse by years of co-residence until the older sibling turned 21 and risk for future drug abuse in adolescents living with parental figures as a function of family-level socioeconomic status and neighborhood social deprivation.

Results: The best twin sibling fit model predicted substantial heritability for drug abuse in males (55%) and females (73%), with environmental factors shared by siblings operating only in males and accounting for 23% of the variance in liability. For each year of living in the same household, the probability of sibling concordance for drug abuse increased 2%-5%. When not residing in the same household, concordance was predicted from residence in the same small residential area or municipality. Risk for drug abuse was predicted both by family socioeconomic status and neighborhood social deprivation. Controlling for family socioeconomic status, each year of living in a high social deprivation neighborhood increased the risk for drug abuse by 2%.

Conclusions: Using objective registry data, the authors found that drug abuse is highly heritable. A substantial proportion of the shared environmental effect on drug abuse comes from community-wide rather than household-level influences. Genetic effects demonstrated in twin studies have led to molecular analyses to elucidate biological pathways. In a parallel manner, environmental effects can be followed up by epidemiological studies to clarify social mechanisms.

FIGURE 1

Relationship Between Living in the Same Household (Number of Years), Age Difference, and Drug Abuse Among Both Siblings in the Pair

FIGURE 2. Relationship Between Living in the Same Household and Drug Abuse Among Both Siblings in the Pair^a

^a The figure illustrates the odds ratio at different number of years living together for different birth year differences.

FIGURE 3. Relationship Between Living in the Same Small Residential Area (Number of Years) and Drug Abuse Among Both Siblings in the Pair^a

^a We divided sibling pairs as a function of the number of years that they were not residing together at home and hence could have been living within the same small residential area.

FIGURE 4. Relationship Between Living in the Same Municipality (Number of Years) and Drug Abuse Among Both Siblings in the Pair^a

^a We divided sibling pairs as a function of the number of years that they were not residing together at home and hence could have been living within the same municipality.