The role of the dopamine 2 receptor gene and personality traits in alcohol dependence within Turkish society
The Role of the Dopamine D2 Receptor Gene and Personality Traits in Alcohol Dependence in the Turkish Population
Arzu DALMIŞ,1 Yıldız AKVARDAR,2 Çiğdem ERESEN,3Sefa KIZILDAĞ,4Uğur AKPULAT,5Şebnem YILDIRIMCAN,6Haluk ARKAR,7 Berna Binnur KIVIRCIK AKDEDE,8 Köksal ALPTEKİN,8
Department of Psychiatry, Faculty of Medicine, Dokuz Eylul University, Balçova, 35340, Izmir, Turkey
Abstract
Objective: This study aimed to investigate the TaqI A and B allele polymorphisms of the dopamine D2 receptor gene (DRD2), personality traits, and the relationship between these two parameters in alcohol-dependent individuals, focusing on the dopaminergic system, which has been shown to be responsible for alcohol-related behaviors in both animal and human studies.
Method: The study included 64 individuals (3 females, 61 males) diagnosed with alcohol dependence according to DSM-IV criteria and 54 healthy controls (8 females, 46 males) with no personal or first- or second-degree family history of alcohol dependence. Blood samples were collected to determine DRD2 TaqI A and B alleles, and participants were administered the Temperament and Character Inventory and the Michigan Alcoholism Screening Test.
Results: No significant difference was found between alcohol-dependent individuals and controls in terms of the frequency of DRD2 TaqI A1 and B1 minor allele polymorphisms. Alcohol-dependent individuals had significantly higher scores in novelty seeking and harm avoidance, and significantly lower scores in self-directedness and cooperativeness compared to controls. No association was found between personality traits and DRD2 TaqI A1 and B1 polymorphisms in alcohol-dependent individuals.
Discussion: Vulnerability to alcohol dependence is likely influenced not by a single gene, but by multiple minor genes, personality traits, and environmental factors. High novelty seeking, associated with increased impulsivity, may play a role in the initiation of addictive behavior, while high harm avoidance may lead to continuous alcohol use as a way to cope with stress.
Keywords: Alcohol dependence, genetics, D2 dopamine receptor gene (DRD2), Temperament and Character Inventory, personality
Introduction
Alcohol dependence is a disorder influenced by biological, psychological, and social factors. Since the 1970s, family, adoption, and twin studies, supported by molecular genetic techniques, have provided strong evidence for the hereditary aspects of alcohol dependence.
Alcohol stimulates neurons in the nucleus accumbens via the mesolimbic system, leading to dopamine release and activation of the brain's reward system, thereby promoting continued alcohol consumption. Because dopamine is the primary neurotransmitter in the reward system, the dopamine gene has been a focus in studies of alcohol susceptibility.
The dopamine D2 receptor (DRD2) gene is located on chromosome 11q22–23. The demonstration by Blum et al. in 1990 of an association between the DRD2 A1 allele and alcohol dependence marked the beginning of research into the relationship between alcohol dependence and the dopaminergic system.
While some studies have found associations between alcohol dependence and DRD2 TaqI A or B alleles, others have not. These inconsistencies may be due to differences in sample size, population characteristics, and methodology.
METHOD
Sample
The study included 64 patients diagnosed with alcohol dependence who applied to or were hospitalized in the Psychiatry Department of Dokuz Eylul University Faculty of Medicine between March 2004 and January 2005. The control group consisted of 54 healthy individuals with no history of alcohol use disorders in themselves or their close relatives. Substance dependence was excluded in both groups.
Participants were between 18 and 65 years of age. The mean age was 47.7±9.5 in the alcohol-dependent group and 39.8±8.3 in the control group.
Measures
Personality traits were assessed using Cloninger’s Temperament and Character Inventory (TCI). The Michigan Alcoholism Screening Test (MAST) was used to assess the severity of alcohol-related problems.
Molecular Genetic Methods
Venous blood samples were collected and DNA was isolated using standard procedures. Polymerase chain reaction (PCR) techniques were used to determine DRD2 TaqI A and B polymorphisms.
Statistical Analysis
Data were analyzed using SPSS 11.0. Categorical variables were compared using chi-square tests and continuous variables using t-tests. Differences were further evaluated using ANCOVA and Pearson correlation analysis.
Results
The mean age of alcohol initiation was 17.4 years, and the average duration of regular alcohol consumption was 18.48 years. Alcohol-dependent individuals consumed alcohol on average 6.2 days per week.
No significant differences were found between groups in genotype distribution. However, A1 and B1 allele frequencies were higher in the alcohol-dependent group.
Alcohol-dependent individuals had significantly higher novelty seeking and harm avoidance scores, and lower self-directedness and cooperativeness scores.
Discussion
The findings suggest that alcohol dependence is influenced by multiple genetic and environmental factors rather than a single gene. Personality traits such as high novelty seeking and harm avoidance play important roles in the development and maintenance of alcohol dependence.
Conclusion
Alcohol dependence should be considered a biopsychosocial disorder. Understanding both genetic and personality-related factors may help improve treatment approaches and outcomes.