If mental illness runs in your family, your genetic makeup may also make you more likely to use drugs and alcohol, suggests new research from Washington University in St. Louis.
The study, published in the online open-access journal Frontiers in Genetics, is among the first to establish a clear genetic connection between individual risk levels for both mental illness and substance abuse, the authors said.
“Our research shows that if someone is genetically predisposed towards having mental illness, they are also prone to use licit and illicit substances and develop problematic usage patterns,” said lead author Caitlin E. Carey, a PhD student in psychological and brain sciences in Arts & Sciences at Washington University.
“This is important because if a mental illness — like depression, runs in your family, you are presumed at risk of that disorder. But we find that having a genetic predisposition to mental illness also places that person at risk for substance use and addiction,” she said.
Conducted with colleagues in the BRAINLab and Department of Psychiatry, both at Washington University, the study analyzed 2,573 unrelated adults to compare risk from mental illness with reported lifetime usage levels for both legal and illegal substances, including alcohol, marijuana, cocaine, nicotine and opioids.
Rather than analyzing family history, Carey and co-authors used information across each person’s genetic code to calculate their genetic risk for various psychiatric conditions, including autism, schizophrenia, bipolar disorder, depression and attention deficit hyperactivity.
“Previous research on the genetic overlap of mental illness and drug use has been limited to family studies, which can make it difficult to examine some less common disorders,” Carey said.
“It’s difficult to find families where some members have schizophrenia and others abuse cocaine,” Carey said. “With our study method, we were able to compare people with various levels of substance involvement to determine whether they were also at relatively higher genetic risk for psychiatric disorders.”
As well as finding an overall genetic relationship between mental health and substance involvement, the study revealed links between specific mental illnesses and drugs, said senior author and BRAINLab director Ryan Bogdan, assistant professor of psychological and brain sciences.
“In addition to evaluating the full spectrum of substance use and misuse, from never-using and non-problem use to severe dependence, this study also allowed us to evaluate specific psychiatric disorder-substance relationships,” Bogdan said. “For example, we found that genetic risk for both schizophrenia and depression are associated with cannabis and cocaine involvement.”
Carey, Bogdan and colleagues hope the study opens new avenues for research aimed at evaluating the predictive power of genetic risk. For example, could genetic risk for schizophrenia predict its onset, severity and prognosis in youth that experiment with marijuana and other drugs?
“It will now be important to incorporate the influence of environmental factors — such as peer groups, neighborhood, and stress — into this research,” Bogdan said. “This will help us better understand how interplay between the environment and genetic risk may increase or reduce the risk of co-occurring psychiatric disorders and substance involvement.
“Further, it will be important to isolate specific genetic pathways shared with both substance involvement and psychiatric illness. Ultimately, such knowledge may help guide the development of more effective prevention and treatment efforts decades in the future.”
Other members of the research team include Arpana Agrawal, Kathleen K. Bucholz, Sarah M Hartz, Elliot Nelson and Laura J. Bierut, all of the Department of Psychiatry at Washington University School of Medicine in St. Louis; and Michael T. Lynskey of the Institute of Psychiatry, Kings College, London.
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