Association of dopamine receptor gene polymorphism and psychological personality traits in liability for opioid addiction.
Opiate addictions is major social and medical problem that impose a significant burden on society. Opioids belong to group of psychoactive substances (PAS), that are commonly abused and produce highly addictive effect. In any of the form of use (natural, semisynthetic or synthetic)--as opium, morphine, kodein or heroin, opioids cause significant health deterioration and its consequences. Although they belong to central nervous system (CNS) sedating agents (sedatives), they cause an euphoria--affective state opposite to depression . According to the International Classification of Diseases, 10th edition (ICD-10) opioid addiction represents a cluster of behavioural, cognitive, and physiological symptoms developped after repeated opiods use. Opioid addiction typically includes a strong desire to take the drug, difficulties in controlling its use and persistance in its use despite harmful consequences . Formal and molecular-genetic studies imply that genetic factors play a significant role in susceptibility and interindividual variability of drug addiction . Although, it has been shown that there is an 8 fold increase in risk for opioid addiction development in first degree relatives, it is not possible to exclude the contribution of environmental effects on particular personality traits linked to this disorder . Moreover, opioid substance abuse is at the most influenced by specific personality characteristics. Neurobiological mechanism of addiction is layed in disturbance of neurophysiological brain functions at reception and transmission of neuronal signals. After opioid intake, i.e. heroin, there is a change in physiologically controlled dopamine release. In longterm opioid addiction, the most important neurochemical mechanisms are prolonged depletion of opioid and dopamine transmission with qualitative and quantitative changes at opiod and dopamine receptors  that affects the rewarding system and brain reinforcement . It has been shown that dopamine receptor type 2 (D2) encoded by DRD2 gene (OMIM rs1800497) is involved in liability to different types of addiction: alcohol, nicotine, cocaine and heroin . Several structural changes within DRD2 have been found and explored as potentially causative variants in development of opioid addiction . DRD2 TaqI, a SNP also known as the TaqIA (or Taq1A) polymorphism of the dopamine D2 receptor is represented with minor (T) and major (C) allele. Minor allele (Taq IA) is associated with a reduced number of dopamine binding sites in the brain and has been postulated to play a role in alcoholism, smoking, and certain neuropsychiatric disorders . Therefore we explored the variation of DRD2 gene polymorphism and personality traits and their potential association with inherited liability to opioid addiction.
MATERIALS AND METHODS
This research was prospectively conducted as case-control study and comprised sample of 200 individuals. Case group consisted of 100 patients included in Program of Metadone Substitution Therapy, previously diagnosed with opioid addiction according to ICD-10 and consecutively recruited during the period of one year. Control group contained 100 subjects clinically confirmed as healthy, with no individual history of substance abuse or psychiatric disorders, age and sex matched to case group individuals. Ethical aspects of the study were approved by institutional ethics committee and all participants signed informed consent prior to any study procedure.
Psychological evaluation was performed for all individuals using Eysenck personality questionnaire (EPQ). Sociodemography data and family history was collected using study questionnaire followed by blood sampling for genetic analysis. DNA was extracted from blood using salting-out procedure  followed by amplification of DRD2 TaqI (rs1800497) flanking region using previously reported method . PCR products were checked for quality on 1% agarose gel and subsequently treated with restriction endonuclease type II under following conditions: 0.5 unit of TaqI per microliter of PCR product was incubated at 37[degrees]C overnight. Restricted fragments were electrophoretically separated on 2% agarose gel and photodocumented using KODAK Edas Software.
Statistical analysis was performed using IBM Statistics --SPSS vi9.0 for Windows i Microsoft Excel 2007.
Total of 200 individuals were recruited to the study under previously defined inclusion criteria. All signed informed consent and after being interviewed, provided blood sample for genetic analysis. DNA was succesfully extracted from all samples that all underwent standard PCR-RFLP procedure according to the protocol explained before. All expected genotypes A1A1, A1A2 and A2A2 have been observed in all individuals. Technician blinded to disease status read out and documented genotypes (Figure 1). Frequencies of A1 and A2 alleles in both populations together were 21.75% and 78.25% respectively. Genotypes frequency distribution in whole observed population was 4%, 35.5% and 60.55 for A1A1, A1A2 and A2A2 genotypes respectively. Sociodemographic parameters analysis showed statistically significant differences between two investigated groups in relation to education level and employment status, work efficiency, problems with law, upbringing conditions, parental marital status and intrafamilial relations. Among patients, 15.2% were upbrought by relatives, 2% individuals were abandoned. All control subjects were raised in primary families. Parental marital status differed between groups: 51.5% and 75.8% in case and control group respectively. 30.9% of patients' parents were widowers and 17.5% were divorced. Family history analysis implies statistically significant differences between groups according to positive familial history for psychiatric disorders (psychoses and substance abuse) p<0.05. Alcohol abuse among first degree relatives of study subjects was more frequent in case (62%) than in control group (Figure 2). Other substances abuse frequency was also increased among first degree relatives of study subjects: 26% and 4% in case and control group respectively. Psychotic and personality disorders of first degree relatives were also overrepresented in case (16%) than in control group (6%) (Figure 3).
[FIGURE 1 OMITTED]
Analysis of primary personality traits determined the presence of high correlation between extraversion /intraversion, psychoticism and neuroticism in heroin abusers. Assessment of general distrubution of these traits pointed increased occurence of neuroticism among patients (84%) as compared to control group (26%); similar pattern was shown for psychoticism (68% in cases and 26% in controls), while intraversion was less overrepresented in case (47 %) than in control group (36%) (Table 1). Analysis of investigated DRD2 locus genotypes showed a similar distribution of observed genotypes in both investigated groups. (Chi-square=2.765; p>0.05). Homozygous genotype variants (A1A1 i A2A2) were overrepresented in case groups while heterozygotes were more frequently observed in control group, but no statistically significant difference was found (Table 2). Analysis of genotype A1A1 frequency showed 6% and 2% in case and control groups respectively (Figure 4). Statistical analysis using McNemar and Fisher exact test for binominal samples, pointed statistically significant overrepresentation of A1A1 genotype in case group, as oposed to expected -normal distribution with OR=1.532 (CH1.0012.344) i p<0.05. This implies that A1A1 carriers have 1.5 fold increased risk for development of heroin addiction.
No statistically significant association of DRD2 TaqI genotypes with any of the investigated personality traits in relation to addiction status. Multivariate analysis of parameters of sociodemography, heredity and Ai allele polymorphism, showed that patients--Ai allele carriers--with added factor of "up-bringing in incomplete family" has 2.7 fold increased risk for developing heroin addiction. Furthermore, patients with positive family history of psychosis and Ai allele carriers showed 3.5 fold increase in risk, while patients who had Ai allele and positive family history of drug abuse had even 4.7 times increase in risk for addiction than A2/A2 carriers (Table 3).
Although current level of knowledge on opioid addiction implies equal liability to this disease, it is clear that certain inherited characteristics of personality play significant role in development of heroin addiction. Results of this study inambiguosly showed that there is a clear overpresentation of basic personality traits (neuroticism, psychoticism, extraversion/intraversion) in group of patients with heroin addiction implying their role in elevation of disease risk as reported previously for different populations [7-9]. A number of studies confirmed an association between DRD2 polymorphism and heroin addiction [10-24]. Our study on DRD2 variation resulted with similar frequency distribution of observed genotypes in both investigated groups (Chis-quare=2.765; p>0.05). However, homozygous genotypes (A1A1 and A2A2) were overrepresented in case group, while heterozygotes (A1A2) were overrepresented in control group with no statistically significant difference observed. Our findings suggest that observation of certain genotype or allele variant (Ai) is not necessarily a single predictive factor for liability for opioid addiction, especially when others (i.e. certain personality trait or enviromental risk factors) are absent which is consistency with previously published data [14,15, 25]. Considering the abovementioned, it is implicated that augmented values for personality traits (neuroticism, psychoticism, extraversion/intraversion and up-bringing in incomplete families) with factors of heredity (i.e. familial history of substance abuse and psychotic disorders) are associated with increased risk for development of opioid addiction. In this study we focused the variation in DRD2 gene with small additive effect in overall incidence of PAS abuse disorders, we can conclude that A1Ai genotype associated with other sociodemographic and hereditary factors may increase individual risk towards opioid addiction development up to 1.5 fold as compared to A1Ai non-carriers but with no direct association with heroin addiction.
Overrepresentation of certain personality traits (neuroticism, psychoticism and extraversion/ intraversion), together with environemental risk factors such as: upbringing within incomplete families and familial history of psychotropic substances abuse, are associated with high risk development of opioid addiction. A1Ai genotype associated with other sociodemographic and hereditary factors may increase individual risk towards opioid addiction up to 1.5 fold as compared to A1Ai non-carrier individuals.
This is the first study in Bosnia and Herzegovina related to study of the associations between genetic and personality factors in the development of heroin addiction. This research was supported by the Institute of Alcoholism and Substance Abuse of Canton Sarajevo, Faculty of Medicine of University of Sarajevo and the Institute for Genetic Engineering and Biotechnology Sarajevo (INGEB). The authors especially thank all the participants in the survey.
DECLARATION OF INTEREST
The authors declare no conflict of interest.
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Nermana Mehic-Basara (1) *, Lilijana Oruc (2), Lejla Kapur-Pojskic (3), Jasmin Ramie (3)
(1) Public Institute for Alcoholism and Substance Abuse Sarajevo, Bolnicka 25, 71000 Sarajevo, Bosnia and Herzegovina. (2) Psychiatric Clinic, Clinical Center University of Sarajevo, Bolnicka 25, 71000 Sarajevo, Bosnia and Herzegovina. (3) Institute for Genetic Engineering and Biotechnology, Zmajaod Bosne 8, Campus, 71000 Sarajevo, Bosnia and Herzegovina.
* Corresponding author: Nermana MehicBasara, MD. PhD, Neuropsychiatrist Phone: +387 33 219 738 Fax: +387 33 202 573 e-mail: firstname.lastname@example.org
Submitted: 25 April 2013 / Accepted: 23 May 2013
TABLE 1. EPQ personality traits in relation to Mean and standard deviation value in both groups N Mean Std. Std. deviation error P Control 100 3.92 2.477 0.248 Case 100 7.61 3.542 0.354 Total 200 5.77 3.566 0.252 E Control 100 14.78 3.751 0.375 Case 100 13.41 3.944 0.394 Total 200 14.10 3.900 0.276 N Control 100 8.19 5.112 0.511 Case 100 16.50 4.713 0.471 Total 200 12.35 6.435 0.455 L Control 100 11.28 4.759 0.476 Case 100 7 29 3.893 0.389 Total 200 9.29 4.776 0.338 C2 Control 100 38.17 6.702 0.670 Cases 100 44 81 7.289 0.729 Total 200 41.49 7.736 0.547 Minimum Maximum F P value value P Control 0 11 Case 2 16 72.898 0.000 Total 0 16 E Control 0 21 Case 3 21 6.335 0.013 Total 0 21 N Control 1 22 Case 4 23 142.833 0.000 Total 1 23 L Control 2 20 Case 1 18 42.110 0.000 Total 1 20 C2 Control 17 57 Cases 27 63 44.973 0.000 Total 17 63 TABLE 2. Analysis of Genotype frequencies among groups Group Total Control Case A1A1 N 2 6 8 % 2.0 6.0 4.0 A2A2 N 59 62 121 % 59.0 62.0 60.5 A1A2 N 39 32 71 % 39.0 32.0 35.5 Total N 100 100 200 % 100.0 100.0 100.0 TABLE 3. Results of multivariate analysis Risk factor B Std. Wald Error Step 1 (a) Incomplete primary -1.260 0.754 2.791 family Number of siblings -0.827 0.273 9.201 Family history of -1.051 0.487 4.662 substance abuse Family history of -1.014 0.542 3.508 psychoses EPQ - L 0.056 0.034 2.724 Constant 4.740 1.741 7.413 Risk factor DF P Exp(B) Step 1 (a) Incomplete primary 1 0.005 0.484 family Number of siblings 1 0.002 0.437 Family history of 1 0.031 0.350 substance abuse Family history of 1 0.051 0.343 psychoses EPQ - L 1 0.099 1.058 Constant 1 0.006 114.427 FIGURE 2. Distribution of hereditary factors /positive family history Control group Case group Family history of 24 62 alcohol abuse Family history of 4 26 psychoactive substances abuse Family history of 6 16 personality disorder Family history of 6 16 psychotic disorder Note: Table made from bar graph. FIGURE 3. EPQ personality traits (N,P,E) distribution in case and control group Controls Cases Neuroticism 26 84 Psychoticism 26 68 Intraversion 36 47 Extraversion 64 53 Note: Table made from bar graph. FIGURE 4. Distribution of genotype frequencies among groups Control Case A1A1 2 6 A2A2 59 62 A1A2 39 32 Note: Table made from bar graph.
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|Author:||Mehic-Basara, Nermana; Oruc, Lilijana; Kapur-Pojskic, Lejla; Ramic, Jasmin|
|Publication:||Bosnian Journal of Basic Medical Sciences|
|Date:||Aug 1, 2013|
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