Potential genetic testing for substance abuse raises hope, concern
Genetic tests using blood samples already are used to diagnose some diseases and even personalize treatment.
Now it is possible to develop similar tests that reveal a person's potential to become dependent on nicotine or marijuana or have antisocial personality disorder, University of Iowa researchers report online March 6 in the American Journal of Medical Genetics.
Such tests would not dictate who would become substance dependent or have behavioral problems, as genes do not function in isolation but are influenced by other genes and environmental factors, said the study's lead author Robert Philibert, M.D., Ph.D., professor of psychiatry in the UI Roy J. and Lucille A. Carver College of Medicine.
"Our study suggests that analyzing the expression of genes in blood could indicate whether a person is susceptible to having a behavioral disorder. Having a particular gene expression change does not by itself predict that a person will act a certain way. However, it can indicate who might have a greater biological basis for engaging in behaviors such as smoking and alcohol or marijuana use," Philibert said.
"What matters most is not whether you have a particular gene but whether the gene is expressed, and what other environmental factors may be at play. Genetic variation in and of itself is not deterministic," he added.
In a related study also published online March 6, Philibert and colleagues reported a potential blood test for panic disorder. Both the panic disorder study and one on substance abuse used data from the Iowa Adoption Studies, which were established by Remi Cadoret, M.D., an internationally renowned UI professor of psychiatry who passed away in 2005.
In this latest study, the researchers found certain differences in the genes of people with a history of smoking compared to those without such a history. In all, 579 genes were more expressed and 584 genes were less expressed in people who had smoked.
Philibert and colleagues recognized both the positive potentials and the ethical concerns that could stem from the research.
"On the one hand you can say there is an ethical risk in identifying people who might be prone to alcohol abuse or smoking and how insurance companies, for example, might use that information," said Tracy Gunter, M.D., UI professor of psychiatry and a study co-author. "Yet there could be benefit in early identification of people at risk of behaviors such as substance abuse.
"Physicians could implement individualized prevention plans and provide personalized treatment, and knowledge of a disorder would give the individual greater knowledge of his or her vulnerability and therefore greater responsibility to manage it," Gunter added.
The technique used to analyze blood is called "transcriptional profiling," said Anup Madan, UI adjunct assistant professor of neurosurgery and an assistant professor at the Institute of Systems Biology in Seattle.
"Transcription profiling involves looking at all the genes -- nearly 30,000 of them -- at one time. We label all the expressed genes by fluorescent tags, and changes in fluorescence intensity are used to identify differential gene expression," Madan explained.
"We can see if there is a pattern of genes for a specific disease. Over time, we can build a map and see what is happening and define relationships between genes," he added.
The team used samples from six subjects in the Iowa Adoption Studies and nine controls to perform the initial profiling. They then used data from 94 adoption study subjects to check for pattern matches at the gene level.
Madan acknowledged the ethical issues, yet potential gains, for individuals' health care.
"Blood is the one substance that passes through all the other organs, and we now have the potential to make it a window into preventing and treating disease," he said. "Practitioners, as well as patients, need to understand the consequences. Fortunately, we have time before tests are developed and become commercially available to think about and discuss the issues."
Gunter added, "Just because we can look at the deep biology of the individual doesn't automatically mean negative outcomes will follow."
The researchers will investigate the data they now have in more detail and see how it compares to findings from other studies.