The risk of abusing drugs is greater - even for adopted children - if the family environment in which they are raised is dysfunctional, according to a new study conducted by a collaborative team from Virginia Commonwealth University and Lund University in Sweden.
Previous research suggests that drug abuse is strongly influenced by a mix of genetic factors and the environment, including influences of family and peers. That research is primarily based on twin studies and typically involves families that are intact. Relatives that share genes and environment make it difficult to determine if the family dysfunction is linked to the drug abuse or if it is genetics at play. There have been no large-scale adoption studies performed to verify the findings, until now.
In the study, published online March 5 in the journal Archives of General Psychiatry, researchers examined how genetic and environmental factors contribute to the risk for drug abuse in adoptees. Using a large and representative adoption sample from Sweden, they demonstrate that genetic factors played a moderate role in the liability to drug abuse.
"For an adoptee, having a biological parent with drug abuse who did not raise you doubles your risk for drug abuse," said first author Kenneth Kendler, M.D., director of the VCU Virginia Institute for Psychiatric and Behavioral Genetics.
"But we also found an important role for environmental factors. If you have an adoptive sibling - with whom you have no genetic relationship - develop drug abuse, that also doubles your risk for drug abuse,"
More importantly, according to Kendler, the team showed that the impact of your genes on risk for drug abuse is much stronger if you are raised in a high-risk rather than a low-risk environment.
"A bad environment can augment the effect of genetic risk on drug abuse," he said.
Kendler, professor of psychiatry, and human and molecular genetics in the VCU School of Medicine, and a team of researchers from Lund University led by Jan Sundquist, M.D., Ph.D., professor and director of the Center for Primary Health Care Research, and Kristina Sundquist, M.D., Ph.D., professor of family medicine at the Center for Primary Health Care Research, analyzed nine public registry data sets compiled between 1961 and 2009 of adoptees and their biological and adoptive relatives from Sweden.
The study population included more than 18,100 adoptees born between 1950 and 1993; 78,079 biological parents and siblings and more than 51,200 adoptive parents and siblings.
Virginia Commonwealth University and Lund University