Dopamine D4 receptor VNTR polymorphism associated with greater risk for substance abuse among adolescents with disruptive behavior disorders: Preliminary results

The impulsive horse: comparing genetic, physiological and behavioral indicators to that of human addiction

Stress and genotype elicit changes in impulse control in a range of species that are attributable to adaptations in both the central and peripheral nervous system. We examined aspects of this mechanism in the horse by assessing the effect of a dopamine receptor genotype (DRD4) and central dopaminergic tone (measured via spontaneous blink rate [SBR] and behavioral initiation rate [BIR]), on measures of impulsivity, compulsivity (3-choice serial reaction time task) and sympathetic/ parasympathetic system balance (heart rate variability [HRV]). Genotype did not have a significant effect on any of the parameters measured. SBR but not BIR correlated significantly with levels of impulsivity. There was no clear association of HRV parameters with either measures of central dopaminergic activity or impulsivity/compulsivity. Overall, some elements of the data suggest that the horse may be a useful animal model for assessing the genetic and environmental factors that lead to the physiological and behavioral phenotype of human addiction, particularly when considering the relationship between central dopaminergic tone and impulsivity.

Association between Polymorphism rs1799732 of DRD2 Dopamine Receptor Gene and Personality Traits among MMA Athletes

Four factors—namely, harm avoidance, novelty seeking, reward addiction and persistence—represent the nature of temperament that is not genetically determined in itself. It was shown in earlier studies that a strong propensity to look for novelty or a tendency to engage in risky behavior is correlated with genetic variants in the area of the genes encoding dopamine receptors. Therefore, the aim of this study is to determine whether there is a relationship between personality traits and genetic variants in the area of the DRD2 dopamine receptor gene in MMA athletes. The participants consisted of 85 mixed martial arts (MMA) athletes and 284 healthy, non-MMA male participants. Their personality traits were measured using the Revised Temperament and Character Inventory. Blood was collected for genetic assays and all samples were genotyped using the real-time PCR method. We observed a statistically significant effect of a complex factor of the DRD2 rs1799732 genotype on MMA participants’ control and reward dependence. Engaging in high-risk sport may be associated with several personality characteristics. The DRD2 rs1799732 polymorphism may be associated with reduced harm avoidance in martial arts athletes, thereby modulating athletes’ predisposition to participate in high-risk sport.

Determination of the Relationship Between Craving and 4-repeat Allele of DRD4 Gene Polymorphism in the Early Withdrawal Period of Alcohol Use Disorders

OBJECTIVE

Alcohol use disorder (AUD) is a disease with chronic relapses. Risk factors of craving, which is thought to be one of the predictors of relapse, have been studied for a long time. The DRD4 gene is located on chromosome 11p and has a 48-base pair variable number of tandem repeat (VNTR) polymorphisms in the 3rd exon. This study aimed to investigate if a relationship existed between craving and DRD4 VNTR polymorphism and to determine the predictors of craving.

METHODS

A total of 125 patients with AUD were included in the study. The sociodemographic data form, the Michigan Alcoholism Screening Test (MAST), the Obsessive Compulsive Drinking Scale (OCDS), and the Penn Alcohol Craving Scale (PACS) were applied to the patients. Polymerase chain reaction (PCR) was used to determine the DRD4 VNTR variant of all participants in the peripheral blood sample.

RESULTS

In the 4R/4R homozygous group, it was found that the age at first alcohol use was higher and the scores of the OCDS on the seventh day were lower, but this relationship could not be demonstrated in further statistical analyses. In the stepwise linear regression model, the age at first alcohol use, MAST score, duration of AUD, and delirium tremens history were found to be the predictors of craving.

CONCLUSION

DRD4 VNTR polymorphism does not play a role as a predictor of craving. A decrease in age at first alcohol use, an increase in the MAST score, and the presence of delirium tremens were found to be the predictors of craving among the participants of this study.

Rates of Dual Diagnosis in Child and Adolescent Psychiatric Inpatients: A Scoping Review

OBJECTIVES

Child and adolescent psychiatric (CAP) inpatient admissions have increased since 2009 and the clinical profile of these patients has become more complex. Unrecognized dual diagnosis, that is, comorbid substance use or substance use disorder (SUD) may contribute to this problem, but the prevalence of dual diagnosis in this population is inadequately understood. The goal of this scoping review was to summarize the range and content of research on this topic.

METHODS

MEDLINE, EMBASE, and PsychINFO databases were systematically searched for studies published from 2008 to 2019 containing information on rates of comorbid substance use or SUD in CAP inpatients.

RESULTS

A total of 23,326 abstracts were located. After removing duplicates, screening abstracts and full-text papers, and extracting data with full-text reviews, fourteen studies meeting our criteria remained. Rates of substance use or SUD ranged from 0.9% to 54.8%, differing on the basis of: (1) type of outcome; (2) type of data source; and (3) whether samples had a specific diagnostic focus or not. Rates of any type of SUD were reported in approximately 25% of samples from administrative databases, in 17.7% to 38.5% of chart reviews, and in 55% of studies with data from clinical research examinations. The highest rates of substance-specific substance use or SUD were for alcohol, cannabis, and nicotine.

CONCLUSIONS

We located 14 studies, but methodologic heterogeneity precluded quantitative calculation of a single estimate for the prevalence of dual diagnosis. However, most of the rates suggest that this is an important problem in CAP inpatients, meriting further research. We suggest ways to improve future studies.

An Integrated Model of Nature and Nurture Factors that Contribute to Addiction and Recovery

BACKGROUND

In the context of the opioid epidemic and growing awareness of addiction as a public health concern, there are efforts to inform the public, patients, families, and policy makers about the factors that contribute to addiction and facilitate recovery. Several theoretical models provide useful frameworks for this discussion, but each of them has limitations.

OBJECTIVES

This paper presents an accessible yet comprehensive theoretical model that integrates empirical evidence about addiction etiology and recovery using the nature-nurture paradigm.

RESULTS

The model presents substance use along a continuum, and identifies risk and protective factors in multiple domains that have been identified by research. The domains on the nature side of the model include genetic and biological factors, comorbid psychiatric and medical disorders, physiological reinforcement of substance use, and changes to neural mechanisms. The domains on the nurture side of the model include sociocultural factors, environmental factors, personality, emotions, cognitions, psychological reinforcement of substance use, and cognitive and behavioral changes. The progression from increased or decreased substance use to addiction or recovery is mediated by changes in neural mechanisms and cognitive and behavioral changes, which have feedback loops with the physiological and psychological reinforcement.Conclusions/Importance: This model is a useful heuristic, consistent with a public health framework, for discussing addiction and recovery with patients, their families, and the public. This integrated model of nature and nurture factors has the potential to inform clinical practice, consultation, research, prevention programs, educational programs, and public policy.

Associations Among Internet Addiction, Genetic Polymorphisms, Family Functioning, and Psychopathological Risk: Cross-Sectional Exploratory Study

BACKGROUND

International research has emphasized that youths are at higher risk for the onset of internet addiction (IA), but studies investigating biological, psychological, and social factors associated with this condition are limited.

OBJECTIVE

This study aims to investigate the possible association between IA and genetic polymorphisms in monoamine oxidase A (MAO-A), serotonin-transporter (5-HTTPR), dopamine receptor (DRD4), and dopamine transporter (DAT1) genes by considering the role played by the perception of young adults in their family functioning and their depression, anxiety, and avoidant personality problems.

METHODS

In a sample of 104 male and female young adults aged between 19 and 23 years (mean age 21.87, SD 2.29 years) recruited from universities in the central southern part of Italy, we addressed the presence of IA using the Young criteria of the IA test. Moreover, the perception of young adults of their family functioning and their psychopathological symptoms were assessed through the Family Assessment Device (FAD) and the Adult Self-Report, respectively.

RESULTS

We found no significant association between IA and any genetic polymorphisms, neither among males or females. Young adults with IA reported significantly higher scores in the subscale of FAD affective responsiveness (AR; P=.01) and in depressive problems (P=.02), anxiety problems (P=.009), and avoidant personality problems (P=.003) than those in the control group. Results of mediation analyses showed a mediation role played by depressive symptoms (B=0.99; 95% CI 0.22 to 1.97) and avoidant personality problems (B=1.09; 95% CI 0.32 to 2.05) of young adults on the relationship between the FAD, AR, and IA. Finally, this relationship was moderated by the genotype of the 5-HTTLPR (P<.001), DAT1 (P<.001), and MAO-A (P<.001) genes in young adults.

CONCLUSIONS

This exploratory study supports the recent evidence on the mutual relationship among biological, individual, and social risk factors associated with IA in young adulthood. Our findings may have important clinical implications for the development of prevention and treatment programs.

[The role of genetic factors in the development of suicidal behavior in individuals with dependence on synthetic cathinones]

OBJECTIVE

To identify polymorphisms in the genes of dopaminergic and serotonergic systems associated with the risk of suicidal behavior in individuals with dependence on synthetic cathinones.

MATERIAL AND METHODS

One hundred and eighty-two men with the diagnosis of Substance dependence (ICD-10 F15) tested positive for metabolites of synthetic cathinones (a-PVP, MDPV) in the urine were studied. Genotyping was performed for rs1800497 DRD2, rs4646984 DRD4, VNTR 40 b.p. SLC6A3, rs27072 SLC6A3, rs6313 HTR2A and rs6296 HTR1B using PCR and RFLP technique.

RESULTS AND CONCLUSION

It was found that the genes of the serotonergic system HTR2A and HTR1B are predictors of the development of some endophenotypes of suicidal behavior in individuals with dependence on synthetic cathinones.

Cannabis Exposure During Critical Windows of Development: Epigenetic and Molecular Pathways Implicated in Neuropsychiatric Disease

PURPOSE OF REVIEW

Cannabis exposure during critical windows of development may have intergenerational physiological consequences disrupting epigenetic programming and marks. This review examines the literature relating to pre-gestational and prenatal cannabinoid exposure and its effect on genes and molecular pathways related to the development of psychiatric disease.

RECENT FINDINGS

Developmental cannabis exposure alters epigenetic processes with functional gene consequences. These include potentially heritable alterations in genes and molecular pathways critical for brain development and associated with autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), schizophrenia, addiction, and other psychiatric diseases. Cannabis consumption and mental health illness in adolescents and young adults are increasing in the United States (U.S.), and recent studies suggest that cannabis consumption during critical periods of brain development could contribute to mental health illness through epigenetic mechanisms. These findings warrant future studies and consideration by regulators and health communicators.

Underlying Susceptibility to Eating Disorders and Drug Abuse: Genetic and Pharmacological Aspects of Dopamine D4 Receptors

The dopamine D4 receptor (DRD4) has a predominant expression in the prefrontal cortex (PFC), brain area strictly involved in the modulation of reward processes related to both food and drug consumption. Additionally, the human DRD4 gene is characterized by a variable number of tandem repeats (VNTR) in the exon 3 and, among the polymorphic variants, the 7-repeat (7R) allele appears as a contributing factor in the neurobiological mechanisms underlying drug abuse, aberrant eating behaviors and related comorbidities. The 7R variant encodes for a receptor with a blunted intracellular response to dopamine, and carriers of this polymorphism might be more tempted to enhance dopamine levels in the brain, through the overconsumption of drugs of abuse or palatable food, considering their reinforcing properties. Moreover, the presence of this polymorphism seems to increase the susceptibility of individuals to engage maladaptive eating patterns in response to negative environmental stimuli. This review is focused on the role of DRD4 and DRD4 genetic polymorphism in these neuropsychiatric disorders in both clinical and preclinical studies. However, further research is needed to better clarify the complex DRD4 role, by using validated preclinical models and novel compounds more selective for DRD4.

Association of the DRD4 exon III and 5-HTTLPR VNTR polymorphisms with substance abuse in Jordanian Arab population

Genetic variations in the dopamine D4 receptor (DRD4) gene and the serotonin transporter (SLC6A4) gene are involved in the aetiology of substance abuse disorder (SUD). The main aim of this study is to evaluate the genetic association of DRD4 (48 bp-VNTR) and SLC6A4 (rs25531 and 5-HTTLPR VNTR) gene polymorphisms with SUD susceptibility among the Jordanian Arab population. This study included 500 SUD patients and 500 healthy matched controls. The VNTR Genetic polymorphisms of DRD4 and SLC6A4 genes were genotyped using conventional polymerase chain reaction (PCR). While, the rs25531 SNP was genotyped using PCR-restriction fragment length polymorphism (PCR-RFLP) technique. The genetic association was analysed using different statistical analyses including chi-square, Fisher exact test and one way ANOVA test. The DRD4 exon III VNTR polymorphism was associated with SUD significantly in case of alleles 4, 7 and genotype 7/7 (P = 0.004, 0.0005 and 0.01, respectively). While, there was no genetic association between the 5-HTTLPR (LL, LS, SS), rs25331 (AA, AG, GG) and tri-allelic (SASA, LASG, LASA, LALG, LALA) genotypes (P = 0.26, 0.71 and 0.52, respectively) and SUD. Moreover, using multinomial regression analysis, the homozygous 7/7 and 2/2 VNTR genotypes of DRD4 gene were nominally significantly associated with a lower risk of addiction (OR = 0.285 with P = 0.003 and OR = 0.447 with P = 0.031, respectively) after adjusting for other covariates. Our findings showed that 4 and 7 repeats and the genotype 7/7 of DRD4 exon III VNTRs polymorphism are involved in the aetiology of SUD among Jordanian population in compared to the 5-HTTLPR polymorphisms.

Genetic association of human Corticotropin-Releasing Hormone Receptor 1 (CRHR1) with Internet gaming addiction in Korean male adolescents

BACKGROUND

The number of people with Internet gaming addiction (IGA) is increasing around the world. IGA is known to be associated with personal characteristics, psychosocial factors, and physiological factors. However, few studies have examined the genetic factors related to IGA. This study aimed to investigate the association between IGA and stress-related genetic variants.

METHODS

This cross-sectional study was conducted with 230 male high school students in a South Korean city. We selected five stress-related candidate genes: DAT1, DRD4, NET8, CHRNA4, and CRHR1. The DAT1 and DRD4 genes were genotyped by polymerase chain reaction, and the NET8, CHRNA4, and CRHR1 genes were genotyped by pyrosequencing analysis. We performed a Chi-square test to examine the relationship of these five candidate genes to IGA.

RESULTS

Having the AA genotype and the A allele of the CRHR1 gene (rs28364027) was associated with higher odds of belonging to the IGA participant group (p = .016 and p = .021, respectively) than to the non-IGA group. By contrast, the DAT1, DRD4, NET8, and CHRNA4 gene polymorphisms showed no significant difference between the IGA group and control group.

CONCLUSIONS

These results indicate that polymorphism of the CRHR1 gene may play an important role in IGA susceptibility in the Korean adolescent male population. These findings provide a justification and foundation for further investigation of genetic factors related to IGA.

Effects of DRD2 splicing-regulatory polymorphism and DRD4 48 bp VNTR on crack cocaine addiction

There is evidence that dopamine receptors D2 (DRD2) and D4 (DRD4) polymorphisms may influence substance use disorders (SUD) susceptibility both individually and through their influence in the formation of DRD2-DRD4 heteromers. The dopaminergic role on the vulnerability to addiction appears to be influenced by sex. A cross-sectional study with 307 crack cocaine addicts and 770 controls was conducted. The influence of DRD2 rs2283265 and DRD4 48 bp VNTR in exon 3 variants, as well as their interaction on crack cocaine addiction susceptibility and severity were evaluated in women and men separately. An association between the DRD2 T allele and crack cocaine addiction was found in women. In this same group, interaction analysis demonstrated that the presence of DRD2-T allele and concomitant absence of DRD4-7R allele were associated with risk for crack cocaine addiction. No influence of DRD2 and DRD4 variants was observed in men regarding addiction severity. This study reinforces the role of dopaminergic genes in externalizing behaviors, especially the influence of DRD2-DRD4 interaction on SUD. This is the fourth sample that independently associated the DRD2-DRD4 interaction with SUD itself or related disorders. In addition, our findings point out to a potential difference of dopaminergic neurotransmission across sex influencing addiction susceptibility.

Cannabis use by women during pregnancy does not influence infant DNA methylation of the dopamine receptor DRD4

Background: Maternal cannabis use in pregnancy is linked with long-term adverse behavioral outcomes in offspring. Epigenetic processes established in utero that affect dopaminergic (reward) signaling may mediate risks. Associations between cannabis use and offspring DNA methylation have not been investigated; however, maternal tobacco smoking in pregnancy is associated with distinct patterns of DNA methylation at birth and beyond. Objectives: To determine whether maternal cannabis use is associated with methylation of the dopamine receptor gene DRD4 promoter in infants. Methods: Mothers in the Triple B study provided detailed information on drug use in each trimester of pregnancy. Buccal swabs were collected from neonates at 8 weeks (n = 804, 51.7% male, and 48.3% female). DRD4 promoter DNA methylation was measured using SEQUENOM MassARRAY. Results: Fifty-seven of the women in the study reported drug use during pregnancy, of whom 44 used cannabis. Of 19 cytosine-phosphate-guanine dinucleotides (CpG) units tested in DRD4, gestational cannabis use was associated with offspring methylation at 1 CpG unit in multivariate models (β + 1.48, CI: 0.02 to 2.93, and p = 0.047). At another site there was weak evidence that both cannabis and other drug use were independently associated with increased methylation, while the association with tobacco was in the reverse direction (cannabis use β + 0.67, CI: −0.12 to 1.46, and p = 0.09; other drug use β + 1.11, CI: 0.17 to 2.05, and p = 0.02; tobacco use β −0.41, CI: −0.85 to 0.03, and p = 0.07). None of the associations would remain significant after correction for multiple testing. Conclusion: There is no strong evidence that maternal cannabis use in pregnancy is associated with offspring DRD4 methylation.