A genetic association for cigarette smoking behavior

"Genetic influences impacting nicotine use and abuse during adolescence: insights from human and rodent studies"

Nicotine use continues to be a major public health concern, with an alarming recent rise in electronic cigarette consumption. Heritability estimates of nicotine use and abuse range from 40-80%, providing strong evidence that genetic factors impact nicotine addiction-relevant phenotypes. Although nicotine use during adolescence is a key factor in the development of addiction, it remains unclear how genetic factors impact adolescent nicotine use and abuse. This review will discuss studies investigating genetic factors impacting nicotine use during adolescence. Evidence from both rodent and human studies will be summarized and integrated when possible. Human adolescent studies have largely included candidate gene studies for genes identified in adult populations, such as genes involved in nicotine metabolism, nicotinic acetylcholine receptor signaling, dopaminergic signaling, and other neurotransmitter signaling systems. Alternatively, rodent studies have largely taken a discovery-based approach identifying strain differences in adolescent nicotine addiction-relevant behaviors. Here, we aim to answer the following three questions by integrating human and rodent findings: 1) Are there genetic variants that uniquely impact nicotine use during adolescence? 2) Are there genetic variants that impact both adolescent and adult nicotine use? and 3) Do genetic factors in adolescence significantly impact long-term consequences of adolescent nicotine use? Determining answers for these three questions will be critical for the development of preventative measures and treatments for adolescent nicotine use and addiction.

A systems omics-based approach to decode substance use disorders and neuroadaptations

Substance use disorders (SUDs) are a group of neuropsychiatric conditions manifesting due to excessive dependence on potential drugs of abuse such as psychostimulants, opioids including prescription opioids, alcohol, inhalants, etc. Experimental studies have generated enormous data in the area of SUDs, but outcomes from such data have remained largely fragmented. In this review, we attempt to coalesce these data points providing an important first step towards our understanding of the etiology of SUDs. We propose and describe a 'core addictome' pathway that behaves central to all SUDs. Besides, we also have made some notable observations paving way for several hypotheses; MECP2 behaves as a master switch during substance use; five distinct gene clusters were identified based on respective substance addiction; a central cluster of genes serves as a hub of the addiction pathway connecting all other substance addiction clusters. In addition to describing these findings, we have emphasized the importance of some candidate genes that are of substantial interest for further investigation and serve as high-value targets for translational efforts.

Translational Research in Nicotine Addiction

While commendable strides have been made in reducing smoking initiation and improving smoking cessation rates, current available smoking cessation treatment options are still only mildly efficacious and show substantial interindividual variability in their therapeutic responses. Therefore, the primary goal of preclinical research has been to further the understanding of the neural substrates and genetic influences involved in nicotine's effects and reassess potential drug targets. Pronounced advances have been made by investing in new translational approaches and placing more emphasis on bridging the gap between human and rodent models of dependence. Functional neuroimaging studies have identified key brain structures involved with nicotine-dependence phenotypes such as craving, impulsivity, withdrawal symptoms, and smoking cessation outcomes. Following up with these findings, rodent-modeling techniques have made it possible to dissect the neural circuits involved in these motivated behaviors and ascertain mechanisms underlying nicotine's interactive effects on brain structure and function. Likewise, translational studies investigating single-nucleotide polymorphisms (SNPs) within the cholinergic, dopaminergic, and opioid systems have found high levels of involvement of these neurotransmitter systems in regulating the reinforcing aspects of nicotine in both humans and mouse models. These findings and coordinated efforts between human and rodent studies pave the way for future work determining gene by drug interactions and tailoring treatment options to each individual smoker.

The Dopamine D4 Receptor (DRD4) Exon 3 VNTR Contributes to Adaptive Personality Differences in an Italian Small Island Population

The search for evolutionary forces shaping the diversity of human personality traits encouraged studies that have found that islanders are relatively closed and introverted, with little interest in the external world. The ‘personality gene flow’ hypothesis was proposed to explain the mechanism underlying this difference, suggesting that the frequency of alleles that influence islander personality traits might progressively increase in the gene pools on islands because of selective emigration of individuals not displaying these alleles. We genotyped 96 individuals from the Italian mainland and 117 from Giglio Island, whose residents were previously assessed regarding their personality traits. We genotyped three polymorphisms: the dopamine D4 receptor (DRD4) exon 3 repeat region, the serotonin–transporter SLC6A4 5–HTTLPR indel and the dopamine transporter SLC6A3 DAT1 3′UTR repeat region. Only the DRD4 exon 3 repeat was hypothesised to show varying allele frequencies because this polymorphism could be associated with human migration and personality traits such as extraversion, openness and novelty seeking. As predicted, no differences in allele frequencies were found for the SLC6A4 and SLC6A3 polymorphisms, whereas significant differences were observed in the frequency of the DRD4 exon 3 alleles. The DRD4.2 repeat was more common in mainlanders, as expected, whereas the DRD4.7 allele was over–represented among islanders who never emigrated. This last result contradicts the suggested association of this allele with long–distance migrations. We suggest that emigration might have caused gene flow out the island that resulted in somewhat unpredictable changes in the frequencies of specific alleles, thus influencing islander personality traits. Copyright © 2013 European Association of Personality Psychology

Rare and common variant discovery in complex disease: the IBD case study

Complex diseases such as inflammatory bowel disease (IBD), which consists of ulcerative colitis and Crohn's disease, are a significant medical burden-70 000 new cases of IBD are diagnosed in the United States annually. In this review, we examine the history of genetic variant discovery in complex disease with a focus on IBD. We cover methods that have been applied to microsatellite, common variant, targeted resequencing and whole-exome and -genome data, specifically focusing on the progression of technologies towards rare-variant discovery. The inception of these methods combined with better availability of population level variation data has led to rapid discovery of IBD-causative and/or -associated variants at over 200 loci; over time, these methods have grown exponentially in both power and ascertainment to detect rare variation. We highlight rare-variant discoveries critical to the elucidation of the pathogenesis of IBD, including those in NOD2, IL23R, CARD9, RNF186 and ADCY7. We additionally identify the major areas of rare-variant discovery that will evolve in the coming years. A better understanding of the genetic basis of IBD and other complex diseases will lead to improved diagnosis, prognosis, treatment and surveillance.

Prediction and Understanding of Resilience in Albertan Families: Longitudinal Study of Disaster Responses (PURLS) - Protocol

Exposure to a natural disaster in childhood can have serious, long-lasting consequences, impacting physical and mental health, development, and learning. Although many children experience negative effects after a disaster, the majority do not, and what differentiates these groups is not well understood. Some of the factors that influence disaster-related outcomes in the midst of adversity include parents' mental health, the home environment, and socioeconomic status. Furthermore, genetics has also a role to play in how children respond to stressors. We had the opportunity to conduct a natural experiment of disaster recovery following the Alberta 2013 Flood. This paper presents the detailed protocol on prediction of resilience in Albertan families, and validation with cortisol data. In addition, data collection procedures, developing resiliency screening tools, candidate gene identification, genotyping, DNA methylation, and genomic analyses are described to achieve the research objectives. This study produced new knowledge by using pre- and post-disaster information on children's health and development, including children's genetics and responses to stress. This information has been identified as important to governments and other organizations invested in early child development. Our comprehensive research plan generates evidence that can be mobilized population-based approaches to improve child and family resiliency.

The dopamine transporter role in psychiatric phenotypes

The dopamine transporter (DAT) is one of the most relevant and investigated neurotransmitter transporters. DAT is a plasma membrane protein which plays a homeostatic role, controlling both extracellular and intracellular concentrations of dopamine (DA). Since unbalanced DA levels are known to be involved in numerous mental disorders, a wealth of investigations has provided valuable insights concerning DAT role into normal brain functioning and pathological processes. Briefly, this extensive but non-systematic review discusses what is recently known about the role of SLC6A3 gene which encodes the dopamine transporter in psychiatric phenotypes. DAT protein, SLC6A3 gene, animal models, neuropsychology, and neuroimaging investigations are also concisely discussed. To conclude, current challenges are reviewed in order to provide perspectives for future studies.

An Assessment and Extension of the Mechanism-Based Approach to the Identification of Age-Period-Cohort Models

Many methods have been proposed to solve the age-period-cohort (APC) linear identification problem, but most are not theoretically informed and may lead to biased estimators of APC effects. One exception is the mechanism-based approach recently proposed and based on Pearl’s front-door criterion; this approach ensures consistent APC effect estimators in the presence of a complete set of intermediate variables between one of age, period, cohort, and the outcome of interest, as long as the assumed parametric models for all the relevant causal pathways are correct. Through a simulation study mimicking APC data on cardiovascular mortality, we demonstrate possible pitfalls that users of the mechanism-based approach may encounter under realistic conditions: namely, when (1) the set of available intermediate variables is incomplete, (2) intermediate variables are affected by two or more of the APC variables (while this feature is not acknowledged in the analysis), and (3) unaccounted confounding is present between intermediate variables and the outcome. Furthermore, we show how the mechanism-based approach can be extended beyond the originally proposed linear and probit regression models to incorporate all generalized linear models, as well as nonlinearities in the predictors, using Monte Carlo simulation. Based on the observed biases resulting from departures from underlying assumptions, we formulate guidelines for the application of the mechanism-based approach (extended or not).

Individual differences in the processing of smoking-cessation video messages: An imaging genetics study

Studies testing the benefits of enriching smoking-cessation video ads with attention-grabbing sensory features have yielded variable results. Dopamine transporter gene (DAT1) has been implicated in attention deficits. We hypothesized that DAT1 polymorphism is partially responsible for this variability. Using functional magnetic resonance imaging, we examined brain responses to videos high or low in attention-grabbing features, indexed by "message sensation value" (MSV), in 53 smokers genotyped for DAT1. Compared to other smokers, 10/10 homozygotes showed greater neural response to High- vs. Low-MSV smoking-cessation videos in two a priori regions of interest: the right temporoparietal junction and the right ventrolateral prefrontal cortex. These regions are known to underlie stimulus-driven attentional processing. Exploratory analysis showed that the right temporoparietal response positively predicted follow-up smoking behavior indexed by urine cotinine. Our findings suggest that responses to attention-grabbing features in smoking-cessation messages is affected by the DAT1 genotype.

Polymorphisms in dopaminergic system genes; association with criminal behavior and self-reported aggression in violent prison inmates from Pakistan

Genetic factors contribute to antisocial and criminal behavior. Dopamine transporter DAT-1 (SLC6A3) and DRD2 gene for the dopamine-2 receptor are dopaminergic system genes that regulate dopamine reuptake and signaling, and may be part of the pathogenesis of psychiatric disorders including antisocial behaviors and traits. No previous studies have analyzed DAT-1 and DRD2 polymorphisms in convicted murderers, particularly from Indian subcontinent. In this study we investigated the association of 40 bp VNTR polymorphism of DAT-1 and Taq1 variant of DRD2 gene (rs1800479) with criminal behavior and self-reported aggression in 729 subjects, including 370 men in Pakistani prisons convicted of first degree murder(s) and 359 control men without any history of violence or criminal tendency. The 9R allele of DAT-1 VNTR polymorphism was more prevalent in convicted murderers compared with control samples, for either one or two risk alleles (OR = 1.49 and 3.99 respectively, P = 0.003). This potential association of DAT-1 9R allele polymorphism with murderer phenotype was confirmed assuming different genetic models of inheritance. However, no genetic association was found for DRD2 Taq1 polymorphism. In addition, a combined haplotype (9R-A2) of DAT-1 and DRD2 genes was associated with this murderer phenotype. Further, 9R allele of DAT-1 was also associated with response to verbal abuse and parental marital complications, but not with other measures pertinent to self-reported aggression. These results suggest that 9R allele, which may influence levels of intra-synaptic dopamine in the brain, may contribute to criminal tendency in this sample of violent murderers of Pakistani origin. Future studies are needed to replicate this finding in other populations of murderers and see if this finding extends to other forms of violence and lesser degrees of aggression.

Externalizing Problem Behavior in Adolescence: Parenting Interacting With DAT1 and DRD4 Genes

This study extends previous gene-by-environment (G × E) research through design and methodological advances and examines alternative hypotheses of diathesis stress, vantage sensitivity, and differential susceptibility. In a sample of 984 adolescents and their parents, we examined whether effects of parental support, proactive, punitive, harsh punitive, and psychological control on externalizing problem behavior are moderated by adolescents' genotype for the dopamine transporter (DAT1) or receptor D4 (DRD4) gene. Results provided evidence for main effects of parenting behavior and DRD4, and multiple interaction effects of which one survived Bonferroni correction. Adolescents carrying a long DRD4 variant were more susceptible to the effects of parental proactive control on aggression, for better and for worse. Critical considerations were made regarding the complexity of G × E research.

Decreased lymphocyte dopamine transporter in romantic lovers

OBJECTIVE

The role of dopamine (DA) in romantic love is suggested by different evidence and is supported by the findings of some brain imaging studies. The DA transporter (DAT) is a key structure in regulating the concentration of the neurotransmitter in the synaptic cleft. Given the presence of DAT in blood cells, the present study aimed to explore it in resting lymphocytes of 30 healthy subjects of both sexes in the early stage of romantic love (no longer than 6 months), as compared with 30 subjects involved in a long-lasting relationship.

METHODS

All subjects had no physical or psychiatric illness. The DAT was measured by means of the [3H]-WIN 35,428 binding and the [3H]-DA reuptake to resting lymphocytes membranes. Romantic love was assessed by a specific questionnaire developed by us.

RESULTS

The results showed that the subjects in the early phase of romantic love had a global alteration of the lymphocyte DAT involving both a decreased number of proteins (Bmax) and a reduced functionality (Vmax).

CONCLUSIONS

Taken together, these findings would indicate the presence of increased levels of DA in romantic love that, if paralleled by similar concentrations in the brain, would explain some peculiar features of this human feeling.

Targeted sequencing identifies genetic polymorphisms of flavin-containing monooxygenase genes contributing to susceptibility of nicotine dependence in European American and African American

BACKGROUND

Smoking is a leading cause of preventable death. Early studies based on samples of twins have linked the lifetime smoking practices to genetic predisposition. The flavin-containing monooxygenase (FMO) protein family consists of a group of enzymes that metabolize drugs and xenobiotics. Both FMO1 and FMO3 were potentially susceptible genes for nicotine metabolism process.

METHODS

In this study, we investigated the potential of FMO genes to confer risk of nicotine dependence via deep targeted sequencing in 2,820 study subjects comprising 1,583 nicotine dependents and 1,237 controls from European American and African American. Specifically, we focused on the two genomic segments including FMO1,FMO3, and pseudo gene FMO6P, and aimed to investigate the potential association between FMO genes and nicotine dependence. Both common and low-frequency/rare variants were analyzed using different algorithms. The potential functional significance of SNPs with association signal was investigated with relevant bioinformatics tools.

RESULTS

We identified different clusters of significant common variants in European (with most significant SNP rs6674596, p = .0004, OR = 0.67, MAF_EA = 0.14, FMO1) and African Americans (with the most significant SNP rs6608453, p = .001, OR = 0.64, MAF_AA = 0.1, FMO6P). No significant signals were identified through haplotype-based analyses. Gene network investigation indicated that both FMO1 and FMO3 have a strong relation with a variety of genes belonging to CYP gene families (with combined score greater than 0.9). Most of the significant variants identified were SNPs located within intron regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals.

CONCLUSIONS

Our findings indicated significant association between FMO genes and nicotine dependence. Replications of our findings in other ethnic groups were needed in the future. Most of the significant variants identified were SNPs located within intronic regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals.

The SLC6A3 gene possibly affects susceptibility to late-onset alcohol dependence but not specific personality traits in a Han Chinese population

Dopaminergic dysfunction has an important role in the pathoetiology of alcohol dependence (AD). The purpose of this study was to determine whether the solute carrier family 6 member 3 (SLC6A3) gene (also known as the dopamine transporter DAT gene) was associated with AD, and whether variants in the SLC6A3 locus were associated with specific personality traits in patients with AD. Sixteen polymorphisms in SLC6A3 were analyzed using 637 patients with AD and 523 healthy controls. To reduce clinical heterogeneity, patients were classified into two subgroups: early-onset AD (EOAD) and late-onset AD (LOAD). The Tridimensional Personality Questionnaire was used to assess the personality traits novelty seeking (NS) and harm avoidance (HA) in the patients with AD. Using allele frequency and genotype distribution comparisons and logistic regression analysis, we found evidence of association between rs6350 and AD (P < 0.05). Following subgroup analysis, we confirmed evidence of an association in patients with LOAD (P = 0.003), but not in patients with EOAD. Heterozygous carriers of the A allele have a nearly 3 times greater risk to develop LOAD compared to individuals who do not have an A allele. Although we found that patients with AD had higher NS and HA scores compared to controls (P < 0.001), we did not find evidence of association between SLC6A3 polymorphisms and either NS or HA in patients with AD using linear regression analysis. The findings from our study indicate that the SLC6A3 gene may have a role in susceptibility to late-onset AD in the Han Chinese population.

Smoking in Patients with Parkinson's Disease: preliminary striatal DaT-SPECT findings

OBJECTIVE

To assess whether cigarette smoking interferes with dopaminergic transmission in current- and never-smoking patients with Parkinson's disease.

MATERIALS AND METHODS

Striatal [123I]FP-CIT single photon emission computed tomography was performed in 67 patients with Parkinson's disease (35 women and 32 men aging 60.8 ± 10.1 years and staging 1.76 ± 0.5 on the Hoehn and Yahr scale). At study time, there were 13 current-smokers and 54 never-smokers.

RESULTS

Current-smokers showed a significantly lower putamen/occipital [123I]FP-CIT ratio and a non-significant trend to a lower caudate/occipital [123I]FP-CIT ratio uptake. Current-smokers were also characterized by a lower off UPDRS-III motor score. A logistic regression analysis adjusted for age, sex, disease duration, Hoehn and Yahr staging, and medication indicated a significant lower [123I]FP-CIT uptake not only in the putamen (odds ratio, 0.1; 95% confidence interval, 0.01 to 0.65; P = 0.02) but also in the caudate (odds ratio, 0.2; 95% confidence interval, 0.04 to 0.71; P = 0.015) as well as a lower UPDRS-III motor score (odds ratio, 0.9; 95% confidence interval, 0.81 to 0.99; P = 0.04) in current-smokers.

CONCLUSIONS

The lower [123I]FP-CIT uptake together with the lower UPDRS-III motor score observed in our current-smokers patients with Parkinson's disease (even taking into account variables that are probably expression of dopaminergic neuron decline and treatment) would support an effect of smoking on dopaminergic synaptic mechanisms.

Meta-analysis update of association between dopamine transporter SLC6A3 gene polymorphism and smoking cessation

The SLC6A3 gene is involved in the dopamine pathway, which influences smoking behavior. This study was conducted to present updated results of a meta-analysis to evaluate the association between SLC6A3 polymorphism and smoking cessation. In total, eight studies were assessed, and 9-repeat alleles and no 9-repeat alleles were compared by smoking cessation outcomes. No significant association between SLC6A3 genotype and smoking cessation was observed for the main analysis (odds ratio = 1.128; 95% confidence interval = 0.981-1.298). In conclusion, the genetic variations in SLC6A3 are not associated with smoking cessation, which is not consistent with the results of the previous meta-analysis.

The significant association of Taq1A genotypes in DRD2/ANKK1 with smoking cessation in a large-scale meta-analysis of Caucasian populations

Although a number of studies have analyzed the relation between the DRD2/ANKK1 gene Taq1A polymorphism and smoking cessation, the results remain controversial. The primary objective of the present study was to determine whether this variant indeed has any effect on smoking cessation. The A1-dominant model that considers A1/* (*=A1 or A2) and A2/A2 as two genotypes and compares their frequencies in current and former smokers was applied. A total of 22 studies with 11,075 subjects were included in the meta-analyses. Considering the potential influence of between-study heterogeneity, we conducted stratified meta-analyses with the Comprehensive Meta-Analysis statistical software (version 2.0). Results based on either cross-sectional or longitudinal studies consistently showed a statistically significant association between Taq1A A1/* genotypes and smoking cessation. Further, a more significant association of the variant with smoking cessation was detected when both types of studies were combined. However, there was marginal evidence of heterogeneity among studies (I(2)=33.9%; P=0.06). By excluding other ethnicities and subjects with cancer, the meta-analysis on the basis of 9487 Caucasians demonstrated that Taq1A A1/* genotypes indeed were significantly associated with smoking cessation under both the fixed- and random-effects models (pooled OR 1.22; 95% CI 1.11-1.34; P=3.9 × 10(-5) for both models). No evidence of between-study heterogeneity or publication bias was observed. Thus, we conclude that the polymorphism of Taq1A has an important role in the process of abstaining from smoking, and smokers carrying A2/A2 genotype have a higher likelihood of smoking cessation than those who carry A1/A1 or A1/A2.

Sibling genes as environment: Sibling dopamine genotypes and adolescent health support frequency dependent selection

While research consistently suggests siblings matter for individual outcomes, it remains unclear why. At the same time, studies of genetic effects on health typically correlate variants of a gene with the average level of behavioral or health measures, ignoring more complicated genetic dynamics. Using National Longitudinal Study of Adolescent Health data, we investigate whether sibling genes moderate individual genetic expression. We compare twin variation in health-related absences and self-rated health by genetic differences at three locations related to dopamine regulation and transport to test sibship-level cross-person gene-gene interactions. Results suggest effects of variation at these genetic locations are moderated by sibling genes. Although the mechanism remains unclear, this evidence is consistent with frequency dependent selection and suggests much genetic research may violate the stable unit treatment value assumption.

Meta-analysis reveals significant association of 3'-UTR VNTR in SLC6A3 with smoking cessation in Caucasian populations

Many studies have examined the association between SLC6A3 3′-UTR VNTR polymorphism and smoking cessation; however, the results are inconclusive, primarily because of the small to moderate-size samples. The primary goal of this study was to determine whether this polymorphism has any effect on smoking cessation by a meta-analysis of all reported studies. We adopted a 9-repeat dominant model that considers 9-repeat and non 9-repeat as two genotypes and compared their frequencies in former vs. current smokers. Eleven studies with 5,480 participants were included. Considering the presence of study heterogeneity and differences in the availability of information from each study, three separate meta-analyses were performed with the Comprehensive Meta-Analysis statistical software (v. 2.0). The first meta-analysis provided evidence of association between the 9-repeat genotype and smoking cessation under the fixed-effects model (pooled odds ratio [OR] 1.13; 95% confidence interval [CI] 1.01, 1.27; P = 0.037) but not in the random-effects model (pooled OR 1.11; 95% CI 0.96, 1.29; P = 0.159). Given the marginal evidence of heterogeneity among studies (P = 0.10; I2 = 35.9%), which likely was caused by inclusion of an Asian-population treatment study with an opposite effect of the polymorphism on smoking cessation, we excluded these data, revealing a significant association between the 9-repeat genotype and smoking cessation under both the fixed- and random-effects models (pooled OR 1.15; 95% CI 1.02, 1.29; P = 0.02 for both models). By analyzing adjusted and unadjusted results, we performed the third meta-analysis, which showed consistently that the 9-repeat genotype was significantly associated with smoking cessation under both the fixed- and random-effects models (pooled OR 1.17; 95% CI 1.04, 1.31; P = 0.009 for both models). We conclude that the 3′-UTR VNTR polymorphism is significantly associated with smoking cessation, and smokers with one or more 9-repeat alleles have a 17% higher probability of smoking cessation than smokers carrying no such allele.

Genetic influence of dopamine receptor, dopamine transporter, and nicotine metabolism on smoking cessation and nicotine dependence in a Japanese population

Background

This study investigated whether polymorphisms of the ankyrin repeat and kinase domain containing 1 gene (ANKK1), which is adjacent to the dopamine D2 receptor gene (DRD2), and the dopamine transporter (SLC6A3) and cytochrome P450 2A6 (CYP2A6) genes influence smoking cessation and nicotine dependence in a Japanese population. In 96 current and former smokers, genotyping frequencies for the ANKK1/DRD2 TaqIA, SLC6A3 VNTR, and CYP2A6 polymorphisms were subjected to chi-square analysis, and regression analyses were used to determine the association of the genotypes of current smokers with a Heavy Smoking Index, in addition to evaluating the effect of the subjects’ smoking history on the association.

Results

Genotyping results suggested that nicotine dependence among current smokers homozygous for the SLC6A3 10r allele was lower than that of smokers carrying the minor alleles, and that the CYP2A6 polymorphism might mediate this association. Furthermore, the age at which current smokers began smoking might moderate the association between their genetic polymorphisms and nicotine dependence.

Conclusions

This study provides preliminary findings on the influence of genetic variants on the smoking phenotypes in a Japanese population.

What can genes tell us about the relationship between education and health?

We use genome wide data from respondents of the Health and Retirement Study (HRS) to evaluate the possibility that common genetic influences are associated with education and three health outcomes: depression, self-rated health, and body mass index. We use a total of 1.7 million single nucleotide polymorphisms obtained from the Illumina HumanOmni2.5-4v1 chip from 4233 non-Hispanic white respondents to characterize genetic similarities among unrelated persons in the HRS. We then used the Genome Wide Complex Trait Analysis (GCTA) toolkit, to estimate univariate and bivariate heritability. We provide evidence that education (h(2) = 0.33), BMI (h(2) = 0.43), depression (h(2) = 0.19), and self-rated health (h(2) = 0.18) are all moderately heritable phenotypes. We also provide evidence that some of the correlation between depression and education as well as self-rated health and education is due to common genetic factors associated with one or both traits. We find no evidence that the correlation between education and BMI is influenced by common genetic factors.

Smoking-specific parenting and smoking onset in adolescence: the role of genes from the dopaminergic system (DRD2, DRD4, DAT1 genotypes)

Although only few studies have shown direct links between dopaminergic system genes and smoking onset, this does not rule out the effect of a gene-environment interaction on smoking onset. Therefore, the aim of this study was to examine the associations between smoking-specific parenting (i.e., frequency and quality of communication and house rules) and smoking onset while considering the potential moderating role of dopaminergic system genes (i.e., DRD2, DRD4, and DAT1 genotypes). Data from five annual waves of the 'Family and Health' project were used. At time 1, the sample comprised 365 non-smoking adolescents (200 younger adolescents, mean age = 13.31, SD = .48; 165 older adolescents, mean age = 15.19, SD = .57). Advanced longitudinal analyses were used (i.e., logistic regression analyses, (dual) latent growth curves, and cross-lagged path models). The results showed a direct effect of quality of communication on smoking onset. No direct effects were found for frequency of communication and house rules. Furthermore, no direct and moderating effects of the DRD2, DRD4, or DAT1 genotypes were found. In conclusion, the findings indicated that the effects of smoking-specific parenting on smoking are similar for adolescent carriers and non-carriers of the dopaminergic system genes.

Genetic Analysis of Polymorphisms in Dopamine Receptor and Transporter Genes for Association with Smoking among Cancer Patients

BACKGROUND

Smoking among Russian cancer patients may be related to variations in the DRD2/ANKK1 (Taq1), DRD4 (exon III VNTR), and SLC6A3 genes.

METHODS

Seven hundred fifty patients provided smoking history and DNA.

RESULTS

Current smokers were more likely to be DRD2 A2 allele carriers versus nonsmokers (former/never smokers; 69 vs. 56%; OR = 1.69; 95% CI 1.13-2.53, p = 0.01) and former smokers (69 vs. 59%; OR = 1.54; 95% CI 0.97-2.46, p = 0.07). Ever smokers (current/former smokers) were more likely to be DRD2 A2 allele carriers versus never smokers (65 vs. 55%; OR = 1.50; 95% CI 1.00-2.27, p = 0.05). The risk of current smoking among DRD2 A2 allele carriers was present if the DRD4 short allele was also present (OR = 1.76; 95% CI 1.12-2.78, p = 0.02), and the risk of ever smoking among DRD2 A2 allele carriers was present if the DRD4 short allele was also present (OR = 1.62; 95% CI 1.02-2.55, p = 0.04). DRD2 A2 allele carriers had a shorter period of previous abstinence versus DRD2 A1 carriers (p = 0.02). Effects were not statistically significant when controlling for multiple comparisons.

CONCLUSIONS

The DRD2 A2 allele may increase the risk of smoking among cancer patients, convergent with studies using non-Western samples. However, additional replication is needed.

A prospective study of the effects of the DRD2/ANKK1 TaqIA polymorphism and impulsivity on smoking initiation

This study tested whether DRD2/ANKK1 TaqIA genotype predicted smoking initiation and subsequent use, and effects were mediated by sensation seeking and negative urgency. Between 2009 and 2012, college never smokers (n = 387) completed six assessments over 15 months; those who reported smoking were classified as initiators. Logistic regression indicated that the A1 allele was associated with initiation (p = .003). This effect was partially mediated by sensation seeking and negative urgency. Effects were stronger in Asian Americans. Findings have implications for improving prevention by including elements focused on urges to seek positive or negative reinforcement. Limitations and future directions are discussed.

Genetics of impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) have been recognised in Parkinson's disease (PD) as adverse effects of dopamine replacement therapy, particularly with dopamine agonists. Although virtually all PD patients are treated with dopaminergic drugs, only a minority will develop hyperdopaminergic states, suggesting predisposing and/or protecting factors. The age at onset, the sex and the dose or type of dopaminergic drugs have been identified as clinical predictive factors. Recent genetic studies have investigated associations between ICD and polymorphisms of genes involved in the dopamine metabolism pathway (COMT, DAT), dopamine receptors (DRD1, DRD2, DRD3, DRD4), serotonin receptors and its transporter (HTR2A, 5HTT), and glutamate receptors (GRIN2B). Although validation in larger and independent cohorts is needed, the results from these studies give us some insights into the pathophysiology of hyperdopaminergic states and may be useful, at term, in personalising antiparkinsonian treatment in clinical practice.

Association of genetic polymorphisms with personality profile in individuals without psychiatric disorders

OBJECTIVE

Population-based twin studies demonstrate that approximately 40-50% of the variability in personality dimensions results from genetic factors. This study assessed selected polymorphisms in the COMT Val158Met, MAOA 3'VNTR, 5HTTLPR, 102T/C 5-HT2A, DAT 3'VNTR and DRD2 exon 8 genes and evaluated their association with personality profiles, anxiety levels, and depressiveness in healthy subjects.

METHODS

This study included 406 unrelated (mean age 38.51 years), mentally and somatically healthy Caucasian subjects of Polish origin. The prevalence of the gene variants mentioned above and their association with personality profiles, anxiety levels, and depressiveness was assessed using the Temperament and Character Inventory, NEO Five-Factor Inventory, Spielberger's State-Trait Anxiety Inventory and Beck's Depression Inventory.

RESULTS

The effects of the 5HTTLPR gene on the s/s genotype and empathy (C2) were lowest in the entire group. The effects of gender, age and the HT2A gene for the T/T genotype and attachment (RD3) were highest in women. The effects of gender, age and the DAT gene on the 9/9 DAT genotype, compassion (C4) and cooperativeness (C) were lowest in women. The effects of gender, age and the COMT gene on the Met/Met genotype and neuroticism (NEU) NEO-FFI were also lowest in women.

CONCLUSIONS

Our results suggest considerable influence of individual genes on the formation of personality traits.

Association of dopamine-related gene alleles, smoking behavior and decline in FEV1 in subjects with COPD: findings from the lung health study

Cigarette smoking is the major risk factor for chronic obstructive pulmonary disease (COPD). Specific dopamine related gene alleles have previously been found to be associated with smoking initiation, maintenance and cessation. We investigated the association between specific dopamine related gene alleles and both change in smoking behavior and lung function change over time in individuals with mild-to-moderate COPD. Subjects included a subset of participants in the Lung Health Study (LHS), a smoking intervention study in smokers with mild to moderate COPD. Smoking status was determined and lung function performed at baseline and annually for 5 years. In post-hoc analyses, we assessed the association of the dopamine receptor (DRD2) TaqI A1(+) allele (A1A1, A1A2 genotypes) and A1(-) allele (A2A2 genotype), and the dopamine transporter (DAT) 9R(+) allele (9R9R and 9R10R genotypes) and 9R(-) allele (10R10R genotype) with both changes in smoking status and lung function in a subset of LHS subjects. No significant associations were noted between variants in these genes and success in smoking cessation. However, in exploratory analyses that did not adjust for multiple comparisons, sustained male (but not female) quitters with the DRD2 A1(-) allele and/or the DAT 9R(+) allele showed an accelerated decline in FEV(1) similar to that of continuing smokers over 5 years after quitting smoking. These preliminary findings suggest that dopamine-related genes may play a role in the progression of COPD, at least in the subset of male ex-smokers whose disease continues to progress despite sustained quitting, and warrants additional confirmatory and mechanistic studies.

Association between temperament in terms of the Regulative Theory of Temperament and DRD4 and DAT1 gene polymorphisms

OBJECTIVES

This is a study of the association between DRD4 exon III VNTR and DAT1 3'-untranslated region polymorphisms on the one hand and temperament assessed with the Formal Characteristics of Behaviour-Temperament Inventory on the other hand.

METHODS

The study was run on 418 participants (314 women and 104 men) aged 18 to 55 years sampled from healthy male and female volunteers recruited from inhabitants of the Warsaw metropolis.

RESULTS

Main effects of sex were found for briskness (F(1,417) = 9.05, P = .003, η(2) = 0.022), perseveration (F(1,417) = 37.83, P < .001, η(2) = 0.085), sensory sensitivity (F(1,417) = 14.16, P < .001, η(2) = 0.003), and emotional reactivity (F(1,417) = 34.67, P < .001, η(2) = 0.078). A significant main effect of DAT1 variant was also found for sensory sensitivity (F(1,417) = 7.36, P = .007, η(2) = 0.018). No main effects of DRD4 on any of the analyzed temperament traits were found. A significant interaction of sex and DRD4 variant was found for sensory sensitivity (F(1,417) = 5.68, P = .018, η(2) = 0.014). No significant 3-way interactions (DAT1 × DRD4 × sex) were found.

CONCLUSIONS

A significant main effect of DAT1 polymorphism on sensory sensitivity and a significant interactive sex/DRD4 effect on that same trait were found.

Additive effects of the dopamine D2 receptor and dopamine transporter genes on the error-related negativity in young children

The error-related negativity (ERN) is a negative deflection in the event-related potential that occurs approximately 50 ms following the commission of an error at fronto-central electrode sites. Previous models suggest dopamine plays a role in the generation of the ERN. We recorded event-related potentials (ERPs) while 279 children aged 5-7 years completed a simple Go/No-Go task; the ERN was examined in relation to the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes. Results suggest an additive effect of the DRD2 and DAT1 genotype on ERN magnitude such that children with at least one DRD2 A1 allele and children with at least one DAT1 9 allele have an increased (i.e. more negative) ERN. These results provide further support for the involvement of dopamine in the generation of the ERN.

Bidirectional influences between parents and children in smoking behavior: a longitudinal full-family model

BACKGROUND

The present study investigated longitudinal associations and bidirectional influences between family members in smoking behavior using a longitudinal full-family design. Family systems provide a powerful social context in which modeling and imitation take place. In current literature, however, bidirectional associations between parents and children in smoking behavior are seldom considered.

METHODS

Participants were 426 families, including mothers, fathers, and 2 adolescent children. Associations were assessed over 5 waves with yearly intervals using a cross-lagged model in structural equation modeling.

RESULTS

Findings demonstrate that families resemble an interactive system affording smoking contagion across family members. Results suggest that associations between parents and children are bidirectional, that is, parental smoking behavior influences adolescent smoking behavior and adolescent smoking behavior influences parental smoking behavior. There is insufficient evidence to conclude that longitudinal associations between family members are generally bidirectional, as only unidirectional longitudinal associations were found between between siblings and partners.

CONCLUSIONS

The present study extends previous research on the intergenerational transmission of smoking behavior by demonstrating bidirectional influences between parents and children in smoking behavior. Moreover, the present study suggests that family members may be susceptible to adjust their smoking behavior across time in response to smoking behavior within the family.

Genetically determined dopamine availability predicts disposition for depression

Although prominent personality theories postulate orthogonality between traits of positive emotionality (PEM) and negative emotionality (NEM), empirical evidence often demonstrates the opposite indicating a negative relationship. Therefore, it is not surprising that dopaminergic (DA) gene loci have been related to traits of positive and of NEM. The present genetic association study investigates the influence of two functional DA gene polymorphisms on Sadness as defined by the Affective Neuroscience Personality Scales (ANPS) in healthy Caucasians (n = 1041). We observed a significant interaction effect between the 10-repeat (10R) allele of the dopamine transporter (DAT1) gene and the methionine (Met) allele of the catechol-O-methyltransferase (COMT) Val158Met polymorphism (F((1,1018)) = 11.11; P < 0.001). Carriers of the 9R/9R and the Val/Val genotype showed dramatically reduced Sadness scores in comparison to the other three genotype configurations. Both the 9R/9R and the Val/Val genotypes characterized by reduced transporter density and high dopamine catabolism, respectively, have been separately related to personality traits of PEM and externalizing behavior in the past. The present findings indicate that gene variations of the DA system previously associated with PEM are at the same time protective against high NEM and can therefore constitute a resilience factor against depression.

The influence of three genes on whether adolescents use contraception, USA 1994-2002

In a further contribution to recent investigations of the relevance of genetic processes for demographic outcomes, we investigate genetic associations with whether adolescents use contraception. Using data from the National Longitudinal Study of Adolescent Health, we find that variants in the dopamine transporter gene DAT1, the dopamine receptor gene DRD2, and the monoamine oxidase gene MAOA are associated with unprotected sexual intercourse. Consistent with previous analyses of these data, the genotypes DRD2*A1/A2, DRD2*A2/A2, DAT1*9R/10R, and MAOA*2R/ are associated with higher odds of unprotected sexual intercourse than other genotypes at these loci. The DRD2 associations apply to both men and women, whereas the other associations apply to women only. These results are robust to controls for population stratification by continental ancestry, do not vary by contraceptive type, and are consistent with previous research showing that these genetic variants are associated with higher rates of impulsivity.

Overnight deprivation from smoking disrupts amygdala responses to fear

Cigarette smoking, a major, yet avoidable, cause of disability and premature death, is the most prevalent form of nicotine addiction. An emerging theme in the neurobiology of nicotine addiction is the integrity of the amygdala. Using functional MRI, amygdala responses during a face perception task were compared between 28 chronic smokers [14 females, 14 males; age, 26.3 (2.8) years; age at onset of smoking, 15.8 (2.6) years; years smoked, 9.1 (2.1); cigarettes per day, 17.1 (3.7); Fagerström test for nicotine dependence score, 4.1 (1.9); exhaled carbon-monoxide level, 17.8 (9.5) ppm] and 28 age- and education-matched nonsmokers [14 females, 14 males; age, 26.9 (2.4) years]. Subjects underwent imaging on two separate occasions 1 week apart: smoking satiety versus overnight smoking deprivation, in a randomized counterbalanced order. Our results show no difference in amygdala responses to faces between nonsmokers and satiated smokers. However, overnight deprivation from smoking was associated with a significantly lowered amygdala response to fear, an effect that was probabilistically mapped to the basolateral amygdala. We suggest that aberrant amygdala reactivity in overnight-deprived smokers may reflect a pre-existing vulnerability to smoking and/or increase the risk of smoking relapse after a cessation attempt.

Correlates of first-episode polarity in a French cohort of 1089 bipolar I disorder patients: role of temperaments and triggering events

OBJECTIVES

As only a few studies so far systematically reported on bipolar patients subtyped according to first-episode polarity, we took the opportunity of having at disposal a large sample of bipolar I patients to specify the characteristics of patients included in these subtypes, with a special focus on temperament and triggering events.

METHODS

A total of 1089 consecutive DSM-IV bipolar I manic inpatients were subtyped in manic onset (MO), depressive onset (DO) and mixed onset (MXO), and assessed for demographic, illness course, clinical, psychometric, comorbidity and temperament characteristics.

RESULTS

The main characteristics of MO patients were a hyperthymic temperamental predisposition, a first episode triggered by substance abuse and an illness course with pure, severe and psychotic mania. In comparison, DO patients had more depressive temperaments, a first episode triggered by stress and alcohol, an illness course with more episodes, cyclicity, suicide attempts, anxious comorbidity and residual symptoms. Although sharing characteristics with either MO or DO, MXO patients had more mixed episodes and cyclothymic temperament.

LIMITATIONS

The following are the limitations of this study: retrospective design, bias toward preferential enrolment of MO patients, and lack of information on the number and polarity of lifetime episodes.

CONCLUSIONS

Findings from this study tend to confirm most of the differences previously evidenced among patients subtyped according to first-episode polarity. Differences found in temperamental predisposition and illness onset triggering events are worth noting and may help target early preventive interventions as well as orientate the search for specific genetic risk factors.

No influence of SLC6A3 40 base VNTR polymorphism on the response to risperidone

Abstract Objectives. The SLC6A3 40 base variable number of tandem repeats (VNTR) polymorphism has been associated with several clinical phenotypes associated with dysregulation of dopamine transmission. However, there is only little evidence about a possible influence of such genetic variant on the response to antipsychotics. The aim of the present study is to investigate whether SLC6A3 40 base VNTR polymorphism could modulate response to risperidone in a sample of Korean schizophrenia subjects. Methods. One hundred and forty-two schizophrenia inpatients were treated with a flexible dose of risperidone. Efficacy was assessed at baseline and at discharge using the scores of the Clinical Global Impression-severity (CGI-S), Brief Psychiatric Rating Scale (BPRS) and Positive and Negative Symptom Score (PANSS). Multivariate analysis of covariance was used to test possible influences of SLC6A3 VNTR variants on clinical scores. Results. None of the genotypes and of the alleles under investigation was associated with clinical scores at discharge or with changes of clinical scores over time. In addition, we also failed to find any association between genotypes and allele frequency distribution in accordance with treatment response defined as a 20% (or 30%) or more reduction in the total PANSS scores from the baseline to the end of treatment. Conclusion. Our findings do not suggest a possible association between SLC6A3 40 base VNTR polymorphism and response to risperidone. However, because of several limitations including the investigation of a single drug, the flexible design of the present study and the absence of a complete coverage of features which could influence the response, further investigations could be required.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

Interaction between serotonin 5-HT2A receptor gene and dopamine transporter (DAT1) gene polymorphisms influences personality trait of persistence in Austrian Caucasians

We examined 89 normal volunteers using Cloninger's Temperament and Character Inventory (TCI). Genotyping the 102T/C polymorphism of the serotonin 5HT2A receptor gene and the ser9gly polymorphism in exon 1 of the dopamine D3 receptor (DRD3) gene was performed using PCR-RFLP, whereas the dopamine transporter (DAT1) gene variable number of tandem repeats (VNTR) polymorphism was investigated using PCR amplification followed by electrophoresis in an 8% acrylamide gel with a set of size markers. We found a nominally significant association between gender and harm avoidance (P=0.017; women showing higher scores). There was no association of either DAT1, DRD3 or 5HT2A alleles or genotypes with any dimension of the TCI applying Kruskal-Wallis rank-sum tests. Comparing homozygote and heterozygote DAT1 genotypes, we found higher novelty seeking scores in homozygotes (P=0.054). We further found a nominally significant interaction between DAT1 and 5HT2A homo-/heterozygous gene variants (P=0.0071; DAT1 and 5HT2A genotypes P value of 0.05), performing multivariate analysis of variance (MANOVA). Examining the temperamental TCI subscales, this interaction was associated with persistence (genotypes: P=0.004; homo-/heterozygous gene variants: P=0.0004). We conclude that an interaction between DAT1 and 5HT2A genes might influence the temperamental personality trait persistence.

The dopamine transporter gene, a spectrum of most common risky behaviors, and the legal status of the behaviors

This study tests the specific hypothesis that the 9R/9R genotype in the VNTR of the dopamine transporter gene (DAT1) exerts a general protective effect against a spectrum of risky behaviors in comparison to the 10R/9R and 10R/10R genotypes, drawing on three-time repeated measures of risky behaviors in adolescence and young adulthood on about 822 non-Hispanic white males from the Add Health study. Our data have established two empirical findings. The first is a protective main effect in the DAT1 gene against risky behaviors. The second finding is that the protective effect varies over age, with the effect prominent at ages when a behavior is illegal and the effect largely vanished at ages when the behavior becomes legal or more socially tolerated. Both the protective main effect and the gene-lifecourse interaction effect are replicated across a spectrum of most common risky behaviors: delinquency, variety of sexual partners, binge drinking, drinking quantity, smoking quantity, smoking frequency, marijuana use, cocaine use, other illegal drug use, and seatbelt non-wearing. We also compared individuals with the protective genotype and individuals without it in terms of age, physical maturity, verbal IQ, GPA, received popularity, sent popularity, church attendance, two biological parents, and parental education. These comparisons indicate that the protective effect of DAT1*9R/9R cannot be explained away by these background characteristics. Our work demonstrates how legal/social contexts can enhance or reduce a genetic effect on risky behaviors.

Chromosome 5p Region SNPs Are Associated with Risk of NSCLC among Women

In a population-based case-control study, we explored the associations between 42 polymorphisms in seven genes in this region and non-small cell lung cancer (NSCLC) risk among Caucasian (364 cases; 380 controls) and African American (95 cases; 103 controls) women. Two TERT region SNPs, rs2075786 and rs2853677, conferred an increased risk of developing NSCLC, especially among African American women, and TERT-rs2735940 was associated with a decreased risk of lung cancer among African Americans. Five of the 20 GHR polymorphisms and SEPP1-rs6413428 were associated with a marginally increased risk of NSCLC among Caucasians. Random forest analysis reinforced the importance of GHR among Caucasians and identified AMACR, TERT, and GHR among African Americans, which were also significant using gene-based risk scores. Smoking-SNP interactions were explored, and haplotypes in TERT and GHR associated with NSCLC risk were identified. The roles of TERT, GHR, AMACR and SEPP1 genes in lung carcinogenesis warrant further exploration.

Genetic Influences on Implicit Measures of Personality

Previous research has revealed various relationships between self-reported personality traits and specific variations in genes influencing serotonergic and dopaminergic pathways. In recent studies, however, personality was repeatedly assessed by the use of more indirect measures, such as the implicit association test (IAT). This tool is assumed to access automatic associations, reflecting the sum of former dispositional behavior and experience. The present study aimed to identify potential genetic effects on personality-related associations measured by the IAT. In a sample of 96 women we found correlations between genetic variations of the serotonin and dopamine transporters (5-HTTLPR and DAT 3’-VNTR) and indirectly measured traits of anxiety and agentic extraversion. In detail, the 5-HTTLPR was linked to the anxiety IAT, whereas the DAT 3-’VNTR was associated with performance in the agentic-extraversion IAT. These findings point out genetic influences on personality-related associations and emphasize the usefulness of the IAT in research on the biological foundations of dispositions.

Influences of polymorphic variants of DRD2 and SLC6A3 genes, and their combinations on smoking in Polish population

BACKGROUND

Polymorphisms in dopaminergic genes may influence cigarette smoking by their potential impact on dopamine reward pathway function. A1 allele of DRD2 gene is associated with a reduced dopamine D2 receptor density, and it has been hypothesised that A1 carriers are more vulnerable to smoking. In turn, the 9-repeat allele of dopamine transporter gene (SLC6A3) has been associated with a substantial reduction in dopamine transporter, what might result in the higher level of dopamine in the synaptic cleft, and thereby protective role of this allele from smoking. In the present study we investigated whether polymorphic variants of DRD2 and SLC6A3 genes and their combinations are associated with the smoking habit in the Polish population.

METHODS

Genotyping for TaqIA polymorphism of DRD2 and SLC6A3 VNTR polymorphism was performed in 150 ever-smokers and 158 never-smokers. The association between the smoking status and smoking phenotypes (related to the number of cigarettes smoked daily and age of starting regular smoking), and genotype/genotype combinations was expressed by ORs together with 95% CI. Alpha level of 0.05, with Bonferroni correction whenever appropriate, was used for statistical significance.

RESULTS

At the used alpha levels no association between DRD2 and SLC6A3 genotypes and smoking status was found. However, A1 allele carriers reported longer abstinence periods on quitting attempts than non-carriers (p = 0.049). The ORs for heavier smoking were 0.38 (0.17-0.88), p = 0.023, and 0.39 (0.17-0.88), p = 0.021 in carriers compared to non-carriers of A1 or *9 allele, respectively, and the OR for this smoking phenotype was 8.68 (2.47-30.46), p = 0.0005 for the A1-/9- genotype combination, relatively to the A1+/9+. Carriers of *9 allele of SLC6A3 had over twice a lower risk to start smoking before the age of 20 years compared to non-carriers (sex-adjusted OR = 0.44; 95% CI: 0.22-0.89; p = 0.0017), and subjects with A1-/9- genotype combination had a higher risk for staring regular smoking before the age of 20 years in comparison to subjects with A1+/9+ genotype combination (sex-adjusted OR = 3.79; 95% CI:1.03-13.90; p = 0.003).

CONCLUSION

Polymorphic variants of DRD2 and SLC6A3 genes may influence some aspects of the smoking behavior, including age of starting regular smoking, the level of cigarette consumption, and periods of abstinence. Further large sample studies are needed to verify this hypothesis.

Dopamine genes and nicotine dependence in treatment-seeking and community smokers

We utilized a cohort of 828 treatment-seeking self-identified white cigarette smokers (50% female) to rank candidate gene single nucleotide polymorphisms (SNPs) associated with the Fagerström Test for Nicotine Dependence (FTND), a measure of nicotine dependence which assesses quantity of cigarettes smoked and time- and place-dependent characteristics of the respondent's smoking behavior. A total of 1123 SNPs at 55 autosomal candidate genes, nicotinic acetylcholine receptors and genes involved in dopaminergic function, were tested for association to baseline FTND scores adjusted for age, depression, education, sex, and study site. SNP P-values were adjusted for the number of transmission models, the number of SNPs tested per candidate gene, and their intragenic correlation. DRD2, SLC6A3, and NR4A2 SNPs with adjusted P-values <0.10 were considered sufficiently noteworthy to justify further genetic, bioinformatic, and literature analyses. Each independent signal among the top-ranked SNPs accounted for approximately 1% of the FTND variance in this sample. The DRD2 SNP appears to represent a novel association with nicotine dependence. The SLC6A3 SNPs have previously been shown to be associated with SLC6A3 transcription or dopamine transporter density in vitro, in vivo, and ex vivo. Analysis of SLC6A3 and NR4A2 SNPs identified a statistically significant gene-gene interaction (P=0.001), consistent with in vitro evidence that the NR4A2 protein product (NURR1) regulates SLC6A3 transcription. A community cohort of N=175 multiplex ever-smoking pedigrees (N=423 ever smokers) provided nominal evidence for association with the FTND at these top ranked SNPs, uncorrected for multiple comparisons.

Understanding genes, environment and their interaction in attention-deficit hyperactivity disorder: is there a role for neuroimaging?

Attention-deficit hyperactivity disorder (ADHD) has an established heritable component, but identifying the genes involved has proven difficult. To date, the two most investigated risk genes in ADHD are the DRD4 and DAT1-genes. However, individual risk genes have only explained up to 1% of the variance in the phenotype, suggesting that they represent only relatively small risk factors for ADHD. As such, the role of environmental factors, gene-gene and gene-environment interactions are being investigated. However, studies have not always been able to address the neurobiological mechanisms by which environmental factors and interactions with genes exert their effect on the ADHD-phenotype. Neuroimaging is being used as a tool to investigate the neurobiological effects of individual risk genes. We suggest it could also be applied to investigate the mechanisms involved in environmental effects and interactions between genetic and environmental factors.