Genetics play a major role in drug addiction. Drug addiction is considered a real disease, sharing many features with other chronic conditions. Heritability means that drug addiction tends to run in families. Scientists are now studying the role of genetics in drug addiction. Researchers estimate that genetic factors account for 50% of a person’s vulnerability to addiction.
According to the World Health Organization (WHO), 2 billion people globally consume alcoholic beverages, and around 76 million of these individuals have an alcohol use problem. It is estimated that 185 million people worldwide consume illicit drugs. This drug problem is a serious global issue. Addictive drugs appear to induce adaptive changes in gene expression in brain reward areas, including the striatum. This shows a mechanism for tolerance and habit formation with negative affect and craving, which persists long after consumption stops. These neuroadaptive changes are major elements in relapse.
Mapping DNA Sequences
The National Institute on Drug Abuse (NIDA) is currently researchers gene variations that make a person at risk for drug addiction. This research effort involves studying deoxyribonucleic acid (DNA), which guides the development of every human cell. Scientists are focused on mapping DNA sequences in drug addicts so as to isolate gene sequences that indicated a high risk for drug addiction. These gene sequences contain guidelines for producing specific proteins, which allow the body to perform normal life functions. The mechanism by which these proteins function indicate if a person may be prone to drug addiction.
In 2004, researchers at the Howard Hughes Medical Institute at Duke University were able to identify a specific protein that had a relationship to learning, memory, and drug addiction. This protein, called PSD-95, was studied in mice. The mice that had low levels of PSD-95 took longer to find their way around a maze and were also more sensitive to cocaine. The investigators concluded that PSD-95 was involved in many types of addiction, because most drugs increase the neurotransmitter dopamine.
In another important clinical study, a Nobel Prize winning neurobiologist and his team found that all drugs work through the brain protein DARPP-32, which is a go-between in various chemical brain actions. When DARPP-32 was removed from the brains of mice, the mice would no longer respond to drugs. This protein is involved with all neurotransmitter actions.
D2 Receptors and Addiction
Many experts believe that the number of a certain type of dopamine receptor, called D2, could be used to predict whether a person will become addicted to heroin, cocaine, or alcohol. Brain imaging tests show that people with fewer D2 receptors are more likely to become addicted to a substance that people with many D2 receptors. The number of D2 receptors a person has in the brain is genetically determined. While environmental factors also contribute to addiction, genetic vulnerability determines who ends up addicted.
Dopamine is manufactured inside the brain from amino acid and tyrosine. Once dopamine is release, receptors uptake the chemical, and receptor sites are specific to the neurotransmitters they are keyed with, which means they accept dopamine but no other brain chemical. Biologists believe that a genetic predisposition to produce fewer dopamine receptors is inherited.
Drug Addiction, Learning Share Common Brain Protein.Duke University press release. Accessed at www.dukehealth.org/health_library/news/7415.
Greengard, Paul. Signal Integration in the Brain, NIDA Science Meeting Summaries and Special Reports. Accessed athttp://archives.drugabuse.gov/meetings/apa/signalintegration.html.
Research Report Series on Cocaine Abuse and Addiction, NIDA Research Reports. Accessed at www.drugabuse.gov/ResearchReports/Cocaine/Cocaine.html.