The link between mental illness and drug use could be genetic after all, a new study has uncovered.
According to researchers from the BRAINLab at Washington University in St. Louis, Missouri, genes that indicate a likelihood of living with mental illness could indicate drug use or abuse in the future.
In this study of about 2,600 subjects, lead author Caitlin E. Carey, a PhD student at Washington University, and the research team compared genetic code to different levels of drug use. Analyzing individual mental illness risk in genetic code was a step beyond studies that look at family histories, according to Carey.
"For example, it's hard to find families where some members have schizophrenia and others abuse cocaine," Carey said in a press release. "With this 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."
Carey and the research team discovered that not only did mental illness risk correlate to level of drug use, but patterns linking specific diseases to particular drugs also emerged.
For example, schizophrenia and depression risk could be linked to high levels of pot and cocaine use, while bipolar disorder was closely linked to "problematic" alcohol use and "severe" cocaine use. Attention Deficit Hyperactivity Disorder (ADHD) was closely linked to nicotine use. Autism was not found to be linked to higher use of drugs or alcohol.
"This is important because if a mental illness, like depression, runs in your family you are presumed at risk of that disorder," Carey said in the release. "But we find that having a genetic predisposition to mental illness also places that person at risk for substance use and addiction."
According to Carey, combining genetic, environmental and social factors when analyzing the link between drug use and mental illness could create more effective treatment plans for both.
"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," Carey said in the release. "Further, it will be important to isolate specific genetic pathways shared with both substance involvement and psychiatric illness."
This study was published August 15 in the journal Frontiers in Genetics.
The National Science Foundation, Mr. and Mrs. Spencer T. Olin Fellowship Program, National Institute on Drug Abuse, Klingenstein Third Generation Foundation, National Institute on Aging and National Institutes of Health funded this study.
Conflicts of interest: LB is listed as an inventor on Issued US. Patent 8,080,371, “Markers for Addiction."
All other authors declared no conflicts of interest.