Chunk #16 — RESULTS — Genetically informative research approaches and their limitations — The relationship between genetics of use and genetics of abuse/dependence?
Genes influencing substance initiation may also impact transitions to substance use disorders. Recognizing this conditional nature of substance use disorders, several genetic studies have modeled the genetic and environmental overlap across substance use and later abuse/dependence. Overwhelmingly, genetic influences on earlier stages of substance use have been found to be heavily correlated with genes influencing continued use and abuse/dependence – however, the source and extent of covariation differs across drugs. For instance,nearly 80-90% of the heritable influences on DSM-IV alcohol abuse/dependence overlap with indices of alcohol consumption.39,40. However, in adolescent samples, the overlap between use and escalation (binge drinking, getting drunk) was moderate 41. Furthermore, particularly for alcohol, shared environment also facilitates escalation of use. A study of Finnish adolescent twins42 examining the genetic overlap across alcohol use, frequency of consumption and problem drinking found that while drinking frequency and problem drinking shared over 50% of their genetic influences, the link between initiation and problem drinking was largely due to shared environment.
