Longitudinal modeling of genetic and environmental influences on self-reported availability of psychoactive substances: alcohol, cigarettes, marijuana, cocaine and stimulants.
BACKGROUND
Although an obvious environmental factor influencing drug use, the sources of individual differences in drug availability (DA) are unknown.


METHODS
This report is based on 1788 adult males from the Mid-Atlantic Twin Registry who participated in a structured telephone interview that included retrospective assessments of DA (cigarette, alcohol, marijuana, cocaine and stimulants) between ages 8 and 25. We fitted a biometric dual change score (DCS) model, adapted for ordinal data, to model latent growth and estimate the genetic and environmental components of variance over time.


RESULTS
DA, despite being considered an environmental risk factor, is under both genetic and environmental control. For cigarette, alcohol, marijuana and cocaine availability, there was an overall increase in additive genetic variance and a decline in shared environmental variance over time. Non-shared environmental variance remained steady. Stimulant availability did not follow this pattern. Instead, there was an upswing in shared environmental effects with increasing age.


CONCLUSIONS
We have modeled the genetic and environmental architecture of changes in DA across adolescence. The rise in additive genetic variance over time coincides with acceleration in the expression of individual differences, probably brought on by an increase in personal freedom and a reduction in social constraints. Understanding the etiology of DA is likely to reveal key components, acting directly or indirectly, in the pathway(s) leading to drug initiation, abuse and dependence.
Gillespie
Nathan A
NA
Department of Psychiatry, Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA 23219-1534, USA. ngillespie@vcu.edu
Kendler
Kenneth S
KS
Prescott
Carol A
CA
Aggen
Steven H
SH
Gardner
Charles O
CO
Jacobson
Kristen
K
Neale
Michael C
MC
D000293:Adolescent; D000328:Adult; D002188:Cannabis; D000697:Central Nervous System Stimulants / Q000600:supply & distribution; D002648:Child; D003042:Cocaine; D004200:Diseases in Twins / Q000453:epidemiology* / Q000235:genetics*; D000431:Ethanol; D020022:Genetic Predisposition to Disease; D006801:Humans; D013287:Illicit Drugs / Q000600:supply & distribution*; D008137:Longitudinal Studies; D008297:Male; D015233:Models, Statistical; D012042:Registries; D012307:Risk Factors; D012931:Social Environment; D019966:Substance-Related Disorders / Q000453:epidemiology* / Q000235:genetics*; D014026:Nicotiana; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D014768:Virginia / Q000453:epidemiology
D000697:Central Nervous System Stimulants; D013287:Illicit Drugs; D000431:Ethanol; D003042:Cocaine