Polymorphisms in the dopamine, serotonin, and norepinephrine transporter genes and their relationship to temperamental dimensions measured by the Temperament and Character Inventory in healthy volunteers

There is evidence for an association between polymorphisms of monoamine transporter genes and temperamental personality traits. Recent findings have shown that interaction of allelic variants of the different genes may contribute to the personality factors. We studied the association between temperamental personality dimensions measured with the Temperament and Character Inventory (TCI) and polymorphisms of the dopamine (DAT), norepinephrine (NET) and serotonin (5-HTT) transporter genes in 127 healthy Polish volunteers. There were no significant differences between means of TCI temperamental dimensions (novelty seeking, reward dependence, persistence and harm avoidance) and the transporter genes compared by ANOVA. There were some significant associations between genotypes and TCI subdimensions. Individuals carrying the A9/A9 DAT genotype have lower RD4 scores (dependence vs. independence) than A10/A10 individuals (3.0 +/- 1.4 vs. 3.5 +/- 1.3); p = 0.01. Examining 5-HTT gene promoter polymorphism, heterozygous individuals (l/s) and individuals with 44-bp deletion (s/s) scored significantly lower in the HA1 subdimension (anticipatory worry and pessimism vs. uninhibited optimism; 4.3 +/- 2.3 vs. 5.5 +/- 2.6) in comparison with individuals without deletion (l/l); p = 0.021. The NET transporter gene polymorphism showed no significant association with any of the temperamental TCI subdimensions.     

An interaction between the serotonin transporter promoter region and dopamine transporter polymorphisms contributes to harm avoidance and reward dependence traits in normal healthy subjects

Summary. There is evidence for an association between polymorphisms of serotonin- and dopamine-related genes and temperamental personality traits. Recent findings have shown that interactions between allelic variants of the different genes may contribute to personality traits. We examined the effects of serotonin transporter-linked promoter region (5-HTTLPR) and dopamine transporter (DAT1) gene polymorphisms for associations with the Temperament and Character Inventory (TCI) temperament subscales in 209 Koreans. We found that the variants of 5-HTTLPR interacted with the DAT1 gene polymorphism to influence the HA and RD temperament subscales of TCI. Neither of these two genes affected any subscales of TCI alone. Controlling for the effects of gender and age, we found significant interactions between 5-HTTLPR and DAT1 genes on Harm Avoidance (HA) and Reward Dependence (RD) as measured by the TCI (Hotelling’s Trace = 3.0, P = 0.02). In the presence of the DAT1 10/10 genotype, subjects of group L of 5-HTTLPR had a significantly higher HA score and significantly lower RD score than those of group S (F = 5.04, df = 1, p = 0.03 and F = 8.35, df = 1, p = 0.004, respectively). These findings suggest that the variants of 5-HTTLPR interacted with the DAT1 gene polymorphism to influence the HA and RD temperament subscales of TCI.     

Association between the dopamine D2 receptor (DRD2) polymorphism and the personality traits of healthy Japanese participants

Background

Dopamine neurotransmitter systems have been associated with reward-related and novelty-seeking personality traits. We investigated the possible relationship between the personality traits measured by the Temperament and Character Inventory (TCI) and the TaqI A and − 141C Ins/Del polymorphisms in the dopamine D2 receptor gene (DRD2).

Methods

The sample consisted of 1084 healthy Japanese medical students and medical staff (age = 29.0 ± 9.7 years), each of whom completed the TCI. Their genomic DNA was isolated from whole blood and genotyped using the TaqMan allele-specific assay method. The associations between gene polymorphisms and the scores for TCI were statistically analyzed by one-way analysis of covariance (ANCOVA) adjusting age. Males and females were analyzed separately. Epstatis was assesses using two-way ANCOVA between the DRD2 and ANKK1 genes.

Results

Men with the Ins/Del genotype of the − 141C Ins/Del polymorphism had significantly higher self-directedness scores than those with the Ins/Ins genotype (p = 0.021). None of the TCI scores differed among women with regard to the three genotype groups of the − 141C Ins/Del polymorphism. The DRD2/ANKK1 Taq1 A polymorphism did not affect any TCI factor for either men or women. An epistatic analysis did not reveal main effects of the two genes with regard to TCI scores, but an ANKK1 × DRD2 interaction significantly predicted TCI scores.

Conclusion

These findings suggest the possibility that the − 141C Ins/Del polymorphism and the DRD2/ANKK1 Taq1 A polymorphism are not strongly linked to personality traits directly, but influences them under the interaction between the DRD2 and ANKK1 genes.     

Minor genetic variants of the dopamine D4 receptor (DRD4) polymorphism are associated with novelty seeking in healthy Japanese subjects

Although an association between the dopamine receptor D4 (DRD4) gene and personality traits had been previously investigated, results from previous studies were not conclusive. This may be due to the method of grouping used, which categorized the gene population into two groups based on the length of the variable number of tandem repeats (VNTR) in exon 3. In the present study, we categorized 616 healthy Japanese subjects into more than two groups by further subdividing the DRD4 48-bp VNTR polymorphism, and compared Temperament and Character Inventory (TCI) scores among the groups. A significant difference was found between the DRD4 48-bp VNTR polymorphism and novelty seeking (p = 0.016). The novelty-seeking scores in the subjects carrying the 5/5 genotype were significantly higher than in those carrying the 2/2 genotype (p = 0.002) or the 4/4 genotype (p = 0.005). However, when the conventional method of grouping was used (i.e., short alleles vs. long alleles), there were no significant associations between the DRD4 VNTR polymorphism and any TCI scores. Our results suggest that minor 5-repeat allele is associated with high novelty-seeking scores in healthy Japanese subjects.     

Transmission disequilibrium studies in early onset of obsessive–compulsive disorder for polymorphisms in genes of the dopaminergic system

The dopaminergic system has been shown to be involved in the aetiology of obsessive–compulsive disorder (OCD). Family studies suggest a higher genetic loading in patients with early onset OCD. Our investigation is the first family-based association study concerning polymorphisms in genes of the dopaminergic system in early onset OCD. We studied polymorphisms within the dopamine-4 receptor gene (DRD4), the dopamine transporter gene (DAT1) and the catecholamine-O-methyltransferase gene (COMT). Associations of alleles of DRD4 and COMT with OCD have previously been reported in adults, while a trend towards an association was found for DAT1 alleles. In our study we observed transmission disequilibrium for the 48-bp repeat polymorphism of the DRD4 gene using the ETDT (P = 0.047) in 69 trios comprising patients with early onset OCD and both of their parents. Post hoc TDT analysis of the DRD4 showed reduced transmission of the 4-repeat allele and a slightly increased transmission rate for the 7- and the 2-repeat allele. No evidence of transmission disequilibrium was detected for alleles of the DAT1 and COMT polymorphisms. These polymorphisms do not appear to play a major role in the genetic predisposition to early onset OCD in our study group.     

Dopamine D4 receptor (DRD4) polymorphism and adaptability trait during infancy: a longitudinal study in 1- to 5-month-old neonates

We have examined the relationship between the common dopamine D4 receptor (DRD4) exon III repeat polymorphism and infants' behavior measured with the Italian version of the Early and Revised Infancy Temperament Questionnaires (EITQ/RITQ) in 122 Italian neonates at 1 and 5 months of life, when the genetic contribution to the behavior can be more clearly assessed. Two-way (genotype × age) analysis of variance revealed a significant correlation with the temperamental subscale of adaptability [F(1, 120)=5.26, P<0.02]. At 1 month of life (early assessment), infants with long (L) DRD4 alleles presented significantly low scores (L 2.61±0.073; S 2.84+0.79; Newman-Keuls P=0.03) in comparison with the high scores of infants with short (S) alleles (L 2.4±0.059; S 2.25±0.57). These differences were not detected at 5 months of life (late assessment), denoting a strong environmental effect at this age on the genetic background. These results confirm and extend the genetic influence of the DRD4 gene in human temperament at birth. Electronic Publication     

Genetic background of ADHD: population studies, genes of the catecholamine system

Attention-deficit hyperactivity disorder (ADHD) begins in early childhood. In this article we review the studies supporting a genetic background of this disorder. ADHD occurs in 3-10% of the general population. Family studies reveal a 5 times more likely frequency of ADHD among first-degree relatives than in the general population. Monozygotic twin concordance rate for ADHD is 81%, whereas for dizygotic twins it is 29%. One of the ADHD predisposing factors is dopaminergic neurotransmission abnormality. According to other studies there is a relationship between polymorphism of dopamine transporter gene (DAT), dopamine receptors genes: DRD2, DRD3, DRD4, DRD5, dopamine-beta-hydroxylase gene (DBH) and catechol-O-methyltransferase gene (COMT) and ADHD. In other articles authors describe abnormalities of the serotonergic system, such as the polymorphism of the serotonin transporter gene (5HTT/SERT), serotonin receptors genes 5HT2A and 5HT1B in the development ofADHD. Another possible factor in ADHD background is the dysregulation of the adrenergic system. The most frequently studied is the connection between polymorphism of norepinephrine transporter gene (NET), adrenergic receptors genes: alpha 2A (ADRA2A), alpha 1C (ADRA1C), alpha 2C and monoamine oxidase A gene (MAO-A).     

Dopaminergic system genes in childhood aggression: Possible role for DRD2

Abstract

Excessive or deficient levels of extracellular dopamine have been hypothesized to contribute to a broad spectrum of mood, motor, and thought abnormalities, and dopaminergic system genes have been implicated in aggressive behaviour from animal and human studies. Objective. We examined selected members of the dopaminergic system genes for association with child aggression. Method. We analyzed polymorphisms in the dopamine transporter DAT1/SLC6A3, dopamine receptor DRD2, and DRD4 genes in our sample of pervasive childhood aggression consisting of 144 cases paired with 144 healthy controls, matched for sex and ethnicity. Results. Aggressive children were significantly more likely to have the at least one copy of the G allele for the DRD2 A-241G polymorphism (genotypic P=0.02; allelic P=0.01). The DRD2 rs1079598 CC genotype was overrepresented in aggressive children compared to controls (genotype P=0.04). The DRD2 TaqIA T allele (P=0.01) and the TT genotype (P=0.01) were also significantly overrepresented in aggressive children. Conclusions. Our preliminary results suggest that three polymorphisms in DRD2 are associated with childhood aggression. Future studies are required to replicate the current results and to further explore the relationship between the dopamine system and aggressive behaviour in children.     

The influence of genetic variants on striatal dopamine transporter and D2 receptor binding after TBI

Dopamine (DA) neurotransmission influences cognition and recovery after traumatic brain injury (TBI). We explored whether functional genetic variants affecting the DA transporter (DAT) and D2 receptor (DRD2) impacted in vivo dopaminergic binding with positron emission tomography (PET) using [¹¹C]βCFT and [¹¹C]raclopride. We examined subjects with moderate/severe TBI (N=12) ∼1 year post injury and similarly matched healthy controls (N=13). The variable number of tandem repeat polymorphism within the DAT gene and the TaqI restriction fragment length polymorphism near the DRD2 gene were assessed. TBI subjects had age-adjusted DAT-binding reductions in the caudate, putamen, and ventral striatum, and modestly increased D2 binding in ventral striatum versus controls. Despite small sample sizes, multivariate analysis showed lower caudate and putamen DAT binding among DAT 9-allele carriers and DRD2 A2/A2 homozygotes with TBI versus controls with the same genotype. Among TBI subjects, 9-allele carriers had lower caudate and putamen binding than 10/10 homozygotes. This PET study suggests a hypodopaminergic environment and altered DRD2 autoreceptor DAT interactions that may influence DA transmission after TBI. Future work will relate these findings to cognitive performance; future studies are required to determine how DRD2/DAT1 genotype and DA-ligand binding are associated with neurostimulant response and TBI recovery.     

Association of polymorphisms of the serotonergic pathways with clinical traits of impulsive-aggression and suicidality in adolescents: A multi-center study

Abstract

Objectives. Suicidal behaviour runs in families. This study evaluated association between common polymorphisms in the serotonergic and adrenergic candidate genes (HTR2A, 5HTTLPR, and MAOA) and suicidality, psychopathology and aggression in adolescents. Methods. Four groups of adolescents were included: Suicidal (N=35) and non-suicidal (N=30) psychiatric inpatients, suicide attempters admitted to three psychiatric emergency rooms (N=51) and a community-based control group (N=95). All were genotyped and underwent psychological assessment for relevant endophenotypes and plasma serotonin content (p5HT) was measured. Results. Homozygosity for the T allele of the HTR2A 102T/C polymorphism was associated with lower impulsivity (P=0.03) and aggression (P=0.01) compared to TC carriers. Low activity MAOA genotypes were associated with suicidality (P=0.04). No association was found between p5HT level and the examined polymorphisms. Conclusions. Our findings are in line with the associations described in adult suicidal population. Further studies are needed to evaluate the gene × environmental interactions in larger samples in an attempt to clarify the possible role of genetic factors in pediatric suicidal and impulsive-aggressive behaviour.     

Temperament profiles, 5-HT2A genotype, and response to treatment with SSRIs in major depression

Variation in antidepressive medication response according to 5-HT2A genotype has been reported in several studies. Temperament has been proposed to be one of the vulnerability factors in mood and anxiety disorders. We studied temperament profiles of 98 patients with major depression and explored the interaction between Temperament and Character Inventory (TCI) temperament dimensions, 5-HT2A genotype (SNPs rs6311, rs6313 and rs7997012) and treatment response. No interactive effects for TCI temperament dimensions and 5-HT2A genotypes on antidepressive treatment response were found.     

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

ObjectivesThis 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.MethodsThe 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.ResultsMain effects of sex were found for briskness (F_1,417 = 9.05, P = .003, η² = 0.022), perseveration (F_1,417 = 37.83, P < .001, η² = 0.085), sensory sensitivity (F_1,417 = 14.16, P < .001, η² = 0.003), and emotional reactivity (F_1,417 = 34.67, P < .001, η² = 0.078). A significant main effect of DAT1 variant was also found for sensory sensitivity (F_1,417 = 7.36, P = .007, η² = 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, η² = 0.014). No significant 3-way interactions (DAT1 × DRD4 × sex) were found.ConclusionsA significant main effect of DAT1 polymorphism on sensory sensitivity and a significant interactive sex/DRD4 effect on that same trait were found.     

Association of DRD4 polymorphism with severity of oppositional defiant disorder,separation anxiety disorder and repetitive behaviors in children with autism spectrum disorder

The objective was to examine whether a common polymorphism in the dopamine D4 receptor gene (DRD4) might be a potential biomarker for behavioral variation within the autism spectrum disorder clinical phenotype. Children (N = 66) were evaluated with a validated mother‐ and teacher‐completed DSM‐IV‐referenced rating scale. Partial eta‐squared (ηp²) was used to gauge the magnitude of group differences: 0.01?0.06 = small, 0.06?0.14 = moderate and > 0.14 = large. Children who were 7‐repeat allele carriers had more severe oppositional defiant disorder behaviors according to mothers’ (ηp² = 0.10) and teachers’ (ηp² = 0.06) ratings than noncarriers, but the latter was marginally significant (P = 0.07). Children who were 7‐repeat allele carriers also obtained more severe maternal ratings of tics (ηp² = 0.07) and obsessions–compulsions (ηp² = 0.08). Findings for maternal ratings of separation anxiety were marginally significant (P = 0.08, ηp² = 0.05). Analyses of combined DRD4 and dopamine transporter gene (DAT1) genotypes approached significance (P = 0.05) for teachers’ ratings of oppositional behavior and mothers’ ratings of tics. DRD4 allelic variation may be a prognostic biomarker for challenging behaviors in children with autism spectrum disorder, but these exploratory findings remain tentative pending replication with larger independent samples.     

卒中后抑郁患者多巴胺代谢系统COMT和DAT基因多态性分析

目的 探讨多巴胺递质代谢相关蛋白儿茶酚氧位甲基转移酶(COMT)Val108/158Met、多巴胺转运体(DAT)40bp可变数目串联重复多态(VNTR)两位点基因多态性与卒中后抑郁(PSD)的关系.方法 选择南方医科大学珠江医院神经内科自2010年1月至2010年6月收治的PSD患者68例作为研究组,同期脑卒中后无抑郁患者91例作为对照组,利用聚合酶链式反应-限制性片段长度多态性(PCR-RFLP)技术分析患者COMT Val108/158Met、DAT 40 bp VNTR位点的基因多态性.结果 COMT基因扩增产物分野生型(G/G)、突变纯合型(A/A)、杂合型(A/G)3种基因型,DAT基因扩增产物分7/7、9/7、10/7、10/9、10/10、11/10、11/11倍重复7种基因型;2组患者COMT等位基因、基因型分布比较差异均有统计学意义(x2=5.703,P=0.017;x2=6.489,P=0.039).研究组男性患者与对照组男性患者之间比较,COMT等位基因、基因型的分布差异均无统计学意义(P＞0.05);研究组女性患者与对照组女性患者之间比较,COMT等位基因、基因型的分布差异均有统计学意义(x2=4.610,P=0.032;x2=6.547,P=0.024);研究组与对照组患者DAT等位基因和基因型的总体分布、杂合度比较差异均无统计学意义(P＞0.05).结论 COMT Val108/158Met基因多态性与PSD发生可能有相关性,而DAT40 bp VNTR基因多态性与PSD发生无明显相关性.

Abstract：

Objective To investigate the association of post-stroke depression (PSD) with gene polymorphisms of catechol-O-methyl transferase (COMT) Val1 08/158Met and dopamine transporter 40bp variable number of tandem repeats (VNTR) in dopamine metabolism system. Methods Sixty-eight patients with PSD and 91 patients only suffered from stroke, admitted to our hospital from January 2010to June 2010, were chosen; the gene polymorphisms ofCOMT Val108/158Met and DAT 40 bp VNTR were analyzed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Results The genotypes of COMT gene amplifications were wild type (G/G),homozygous mutant type (A/A) and heterozygous type (A/G); 7 repeated genotypes (7/7, 9/7, 10/7, 10/9,10/10, 11/10 and 11/11) were noted in the DA T gene amplifications; frequencies of COMT alleles and genotypes were significantly different between the 2 groups (x2=5.703, P=0.017;x2=6.489, P=0.039). The frequencies of COMT alleles and genotypes were significantly different between the 2 female groups (x2=4.610, P=0.032;x2=6.547, P=0.024), but no significant differences were found between the 2 male groups (P＞0.05). The frequencies and heterozygosity of DAT alleles and genotypes showed no obvious differences between the 2 groups (P＞0.05). Conclusion The gene polymorphism of COMT Val108/158Met may be associated with PSD, while that of DAT 40bp VNTR is not.     

Interaction of the DRD3 and BDNF gene variants in subtyped bipolar disorder

Objectives

Bipolar disorder is a severe mental disorder with prominent genetic etiologic factors. Dopaminergic dysfunction has been implicated in the pathogenesis of bipolar disorder, which suggests that the dopamine D3 receptor gene (DRD3) is a strong candidate gene. The brain-derived neurotrophic factor (BDNF) gene has been implicated in the etiology of bipolar disorder. We examined the association between the BDNF Val66Met and DRD3 Ser9Gly polymorphisms with two subtypes of bipolar disorder: bipolar-I and -II. Because BDNF regulates DRD3 expression (1), we also examined possible interactions between these genes.

Methods

We recruited 964 participants: 268 with bipolar-I, 436 with bipolar-II, and 260 healthy controls. The genotypes of the BDNF Val66Met and DRD3 Ser9Gly polymorphisms were determined using polymerase chain reactions plus restriction fragment length polymorphism analysis.

Results

Logistic regression analysis showed a significant main effect for the Val/Val genotype of the BDNF Val66Met polymorphism (P = 0.020), which predicted bipolar-II patients. Significant interaction effects for the BDNF Val66Met Val/Val genotype and both DRD3 Ser9Gly Ser/Ser and Ser/Gly genotypes were found only in bipolar-II patients (P = 0.027 and 0.006, respectively).

Conclusion

We provide initial evidence that the BDNF Val66Met and DRD3 Ser9Gly genotypes interact only in bipolar-II disorder and that bipolar-I and bipolar-II may be genetically distinct.     

多巴胺D2、D3受体基因多态性与汉族人精神分裂症相关研究

目的探索多巴胺D2受体(Dopamine D2receptor,DRD2)基因第8外显子Taq I A位点多态和多巴胺D3受体(Dopamine D3receptor,DRD3)基因第5内含子Msp I位点多态与汉族人群精神分裂症是否关联及其在不同性别是否存有差异。方法使用聚合酶链反应-限制性片段长度多态性(Polymerase chain reaction-re-striction fragment length polymorphism,PCR-RFLP)及DNA测序技术,对317例精神分裂症患者及310名对照DRD2Taq I A基因多态性和DRD3Msp I位点基因多态性进行检测。结果患者组与对照组间DRD2 Taq I A位点等位基因分布差异显著(P<0.01)、两两基因型对比(A1/A2与A1/A1相比:P<0.05;A2/A2与A1/A1相比:P<0.01)及两基因型联合对比(A1/A2+A2/A2与A1/A1:P<0.01)组间差异也显著。性别分层研究DRD2Taq I A位点女性组间差异显著(P<0.01),男性组间差异无意义(P>0.05)。DRD3Msp I位点的基因型频率、等位基因分布及性别分层分析等所有数据均显示患者组与对照组之间差异无统计学意义(P>0.05)。风险因子趋势检验结果DRD2Taq I A位点等位基因A2:P<0.01;DRD3Msp I位点等位基因2:P>0.05。结论所得数据支持DRD2Taq I A位点等位基因A2可能为精神分裂发生的风险因子,特别对女性而言。数据分析不支持DRD3Msp I位点基因与精神分裂发生有关。此结果需更进一步研究证实。     

Association of dopamine gene variants,emotion dysregulation and ADHD in autism spectrum disorder

The aim of the present study was to evaluate the association of dopaminergic gene variants with emotion dysregulation (EMD) and attention-deficit/hyperactivity disorder (ADHD) symptoms in children with autism spectrum disorder (ASD). Three dopamine transporter gene (SLC6A3/DAT1) polymorphisms (intron8 5/6 VNTR, 3′-UTR 9/10 VNTR, rs27072 in the 3′-UTR) and one dopamine D2 receptor gene (DRD2) variant (rs2283265) were selected for genotyping based on à priori evidence of regulatory activity or, in the case of DAT1 9/10 VNTR, commonly reported associations with ADHD. A sample of 110 children with ASD was assessed with a rigorously validated DSM-IV-referenced rating scale. Global EMD severity (parents’ ratings) was associated with DAT1 intron8 (ηp² = .063) and rs2283265 (ηp² = .044). Findings for DAT1 intron8 were also significant for two EMD subscales, generalized anxiety (ηp² = .065) and depression (ηp² = .059), and for DRD2 rs2283265, depression (ηp² = .053). DRD2 rs2283265 was associated with teachers’ global ratings of ADHD (ηp² = .052). DAT1 intron8 was associated with parent-rated hyperactivity (ηp² = .045) and both DAT1 9/10 VNTR (ηp² = .105) and DRD2 rs2283265 (ηp² = .069) were associated with teacher-rated inattention. These findings suggest that dopaminergic gene polymorphisms may modulate EMD and ADHD symptoms in children with ASD but require replication with larger independent samples.     

Association of VNTR polymorphisms in the MAOA promoter and DRD4 exon 3 with heroin dependence in male Chinese addicts

Objective. To explore the involvement of variable number tandem repeat (VNTR) polymorphisms in the monoamine oxidase A (MAOA) promoter and exon 3 of the dopamine D4 receptor (DRD4) gene in heroin addiction modulate the vulnerability of individuals to heroin addiction. Methods. Eight hundred and ninety-four male heroin addicts without other psychiatric disorders, were recruited as subjects. Another community 180 males were selected randomly as controls. Results. The geno-distribution of the DRD4 exon 3 VNTR polymorphism in controls was in Hardy–Weinberg equilibrium (HWEχ²=0.925), but the distribution in heroin addicts was not (HWEχ²=28.35). The long-repeat alleles of the DRD4 exon 3 VNTR polymorphism were found more frequently in the heroin addicts (P=0.019). However, the long-repeat alleles of the MAOA promoter VNTR polymorphism were not (P=0.828). No interaction between these two VNTR polymorphisms was found by using multiple logistic regression analysis (P=0.261). Conclusion. The long-repeat allelic variants (>4-repeats) and 2-repeat allele of the DRD4 exon 3 VNTR polymorphism might be risk alleles for individual vulnerability to heroin addiction in Chinese men, but the MAOA promoter VNTR polymorphism does not mean that the partial dominant inherited mode might involved in the genetics of heroin dependence.     

C957T polymorphism of dopamine D2 receptor gene affects striatal DRD2 in vivo availability by changing the receptor affinity

The C957T polymorphism of the human dopamine D2 receptor gene (DRD2) regulates DRD2 availability in striatum in vivo. Specifically, the T allele predicts high DRD2 availability in healthy volunteers (T/T>T/C>C/C). However, this finding was unexpected as in vitro the T allele is associated with a decrease in DRD2 mRNA stability and synthesis of the receptor through a putative alteration in the receptor mRNA folding. To elucidate further how changes in DRD2 density (B_max) and affinity (K_D) contribute to the differences in DRD2 availability between the C957T genotypes, we studied these parameters separately in a sample of 45 healthy volunteers. The subjects had two PET scans with [¹¹C]raclopride (high and low specific radioactivity scans) for the estimation of B_max and K_D, and were genotyped for the C957T. Moreover, the role of the related and previously studied functional TaqIA polymorphism of ankyrin repeat and kinase domain containing 1 (ANKK1) gene was reassessed for comparative purposes. The results indicate that the C957T increased binding potential by decreasing DRD2 K_D (C/C>C/T>T/T), while B_max was not significantly altered. These preliminary findings indicate that the C957T genotype‐dependent changes in DRD2 availability are driven by alterations in receptor affinity and putatively in striatal dopamine levels. This mechanism seems to differ from that observed previously for the ANKK1 gene TaqIA polymorphism, where the minor allele (A1) affects DRD2 availability predominantly by changing B_max. The hypothesis that the two SNPs may have independent effects on dopamine neurotransmission needs to be further tested. Synapse 63:907–912, 2009. © 2009 Wiley‐Liss, Inc.     

COMT genotype affects brain white matter pathways in attention‐deficit/hyperactivity disorder

Increased dopamine availability may be associated with impaired structural maturation of brain white matter connectivity. This study aimed to derive a comprehensive, whole‐brain characterization of large‐scale axonal connectivity differences in attention‐deficit/hyperactivity disorder (ADHD) associated with catechol‐O‐methyltransferase gene (COMT) Val158Met polymorphism. Using diffusion tensor imaging, whole‐brain tractography, and an imaging connectomics approach, we characterized altered white matter connectivity in youth with ADHD who were COMT Val‐homozygous (N = 29) compared with those who were Met‐carriers (N = 29). Additionally, we examined whether dopamine transporter gene (DAT1) and dopamine D4 receptor gene (DRD4) polymorphisms were associated with white matter differences. Level of attention was assessed using the continuous performance test before and after an 8‐week open‐label trial of methylphenidate (MPH). A network of white matter connections linking 18 different brain regions was significantly weakened in youth with ADHD who were COMT Met‐carriers compared to those who were Val‐homozygous (P < 0.05, family‐wise error‐corrected). A measure of white matter integrity, fractional anisotropy, was correlated with impaired pretreatment performance in continuous performance test omission errors and response time variability, as well as with improvement in continuous performance test response time variability after MPH treatment. Altered white matter connectivity was exclusively based on COMT genotypes, and was not evident in DAT1 or DRD4. We demonstrated that white matter connectivity in youth with ADHD is associated with COMT Val158Met genotypes. The present findings suggest that different layers of dopamine‐related genes and interindividual variability in the genetic polymorphisms should be taken into account when investigating the human connectome. Hum Brain Mapp, 36:367–377, 2015. © 2014 Wiley Periodicals, Inc.