The dopamine transporter and neuroimaging in attention deficit hyperactivity disorder

There is evidence that abnormalities within the dopamine system in the brain play a major role in the pathophysiology of attention deficit hyperactivity disorder (ADHD). For instance, dopaminergic psychostimulants, the drugs of first choice in ADHD, interact directly with the dopamine transporter (DAT). Molecular genetic studies suggest involvement of a polymorphism of the DAT gene in ADHD. More recent imaging studies show abnormalities in various brain structures, but particularly in striatal regions. In the current paper we review recent studies in this area. First in vivo measurements of DAT with single photon emission computed tomography (SPECT) in ADHD patients revealed an elevation of striatal DAT density. No differences in DAT density between the left and right side and between putamen and caudate nucleus have been found in [99mTc]TRODAT-1 SPECT of ADHD patients. Patients with ADHD and with a history of nicotine abuse both displayed lower values of DAT density in [99mTc]TRODAT-1 SPECT than non-smokers with ADHD. DAT seem to be elevated in non-smoking ADHD patients suffering from the purely inattentive subtype of ADHD as well as in those with the combined or purely hyperactive/impulsive subtype.     

Unaltered dopamine transporter availability in adult attention deficit hyperactivity disorder

OBJECTIVE: The authors examined whether patients with attention deficit hyperactivity disorder (ADHD) have altered striatal dopamine transporter levels, which may explain psychostimulant effects in this disorder. METHOD: Single photon emission computed tomography and [(123)I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([(123)I]beta-CIT) were used to assess dopamine transporter availability in nine adult patients with ADHD (eight of whom were stimulant naive) and nine age- and gender-matched healthy comparison subjects. RESULTS: Striatal [(123)I]beta-CIT binding did not differ significantly between the ADHD and comparison subjects. CONCLUSIONS: The findings suggest that a hypothesized dysregulation of dopamine function in ADHD does not entail altered dopamine transporter levels.     

The dopamine transporter: relevance to attention deficit hyperactivity disorder (ADHD)

The dopamine transporter is elevated in adults with attention deficit hyperactivity disorder (ADHD) compared with healthy controls [Lancet 354 (1999) 2132]. The findings have been confirmed by others in a different population using a different probe for the dopamine transporter. Notwithstanding the need to confirm these findings in a multi-center trial, several hypotheses are presented to account for these observations. A premise that elevated transporter levels result from medication is not supported by current data. Other possibilities, including hypertrophy of dopamine neuronal terminals in the striatum, dysfunctional regulation of dopamine or dopamine receptors, or anomalies in the dopamine transporter gene are presented as hypotheses. The feasibility of exploring these mechanisms in animal models or in human subjects is explored.     

多巴胺转运体基因与注意缺损多动障碍

目的　探讨注意缺损多动障碍（ＡＤＨＤ） 与多巴胺转运体（ＤＡＴ１） 基因间的关系。方法　分别采用基于单体型和基于基因型的单体型相对风险分析方法,在上海地区汉族人群中对ＡＤＨＤ 与ＤＡＴ１ 基因微卫星多态性进行遗传关联分析。结果　①上海地区汉族人中,ＤＡＴ１ 基因多态以４８０ ｂｐ 重复片段为主,其基因频率为９２％ 。②以父母双亲为对照,经ＧＨＲＲ 和ＨＨＲＲ 分析,ＤＡＴ１ 基因与ＡＤＨＤ 均无关联。结论　上海地区汉族人群中ＤＡＴ１ 基因多态与ＡＤＨＤ 无关。     

The dopamine transporter gene is associated with attention deficit hyperactivity disorder in a Taiwanese sample

Genetic variation of the dopamine transporter gene (DAT1) is of particular interest in the study of attention-deficit hyperactivity disorder (ADHD), since stimulant drugs interact directly with the transporter protein. Association between ADHD and the 10-repeat allele of a 40-bp VNTR polymorphism that lies within the 3'-UTR of DAT1 was first reported in 1995, a finding that has been replicated in at least six independent samples from Caucasian populations. We analysed the DAT1 polymorphism in a sample of 110 Taiwanese probands with a DSM-IV diagnosis of ADHD and found evidence of increased transmission of the 10-repeat allele using TRANSMIT (chi(2)=10.8, 1 d.f., p=0.001, OR=2.9, 95% CI 1.4-6.3). These data give rise to a similar odds ratio to that observed in Caucasian poplulations despite a far higher frequency of the risk allele in this Taiwanese population; 82.3% in the un-transmitted parental alleles and 94.5% in the ADHD probands. These data support the role of DAT1 in ADHD susceptibility among Asian populations.     

5-羟色胺转运体基因多态与共患学习困难的儿童注意缺陷多动障碍的相关性

目的探讨共患学习困难(LD)的注意缺陷多动障碍(ADHD)患儿与5-羟色胺转运体(5-HTT)基因连锁多态区(5-HTTLPR)和第2内含子17 bp数目可变的顺向重复(stin2.VNTR)的关联关系。方法对126例共患LD的ADHD患儿和198例不共患LD的ADHD患儿的5-HTTLPR和stin2.VNTR两种多态进行检测,并采用传递不平衡检测(TDT)和单体型分析方法进行关联分析。结果(1)TDT检测:5-HTTLPR多态的S等位基因在共患LD的ADHD和ADHD混合型(ADHD-C)核心家系中优先传递(X2=5.831和5.281,P=0.015和0.020);所有家系均未观察到stin2.VNTR多态中的任何等位基因有传递不平衡现象(均P>0.05);(2)单体型分析:5-HTT基因与共患LD的ADHD和ADHD-C相关联(X2=11.391和13.343,v=3,P=0.010和P=0.004);单体型L／12在共患LD的ADHD和ADHD-C核心家系中传递较少(X2=10.317和8.948,v=1,P=0.001和0.003),而单体型L／10在共患LD的ADHD核心家系中传递较多(X2=4.065,v=1,P=0.044)。结论5-HTT基因可能与共患LD的ADHD相关联,其中主要为共患LD的ADHD-C亚型。     

A family-based and case-control association study of the dopamine D4 receptor gene and dopamine transporter gene in attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a highly heritable psychiatric condition of early childhood onset characterised by marked inattention, hyperactivity and impulsiveness. Molecular genetic investigations of ADHD have found positive associations with the 480-bp allele of a VNTR situated in the 3' untranslated region of DAT1 and allele 7 of a VNTR in exon 3 of DRD4. A number of independent studies have attempted to replicate these findings but the results have been inconsistent. We used both family-based and case control approaches to examine these polymorphisms in a sample of 137 children diagnosed with ICD-10, DSM-IV or DSM-III-R ADHD. We found no evidence of association with the DAT1 polymorphism, despite a sample size that has up to 80% power to detect a previously reported effect size. We observed a significant increase in the DRD4 7 repeat allele amongst ADHD probands (21.7%) and their parents (18.9% in mothers, 22.3% in fathers), compared to ethnically matched controls (12.8%). However TDT analysis showed no preferential transmission of allele 7 to ADHD probands.     

A preliminary report of the dopamine receptor D4 and the dopamine transporter 1 gene polymorphism and its association with attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent childhood-onset psychiatric syndromes affecting 5%–10% of school-age children worldwide. Distortions in the catecholaminergic system seem to be responsible for this condition. Within this system there are several candidate genes, the dopamine receptor D₄ (DRD4) and the dopamine transporter 1 (DAT1), with common polymorphism which might be associated with ADHD. We performed a family based association study with 36 trios and 19 parent proband pairs. All diagnoses were confirmed by the “Hypescheme” diagnostic computer program. In this study we did not observe an association of ADHD with DRD4 and DAT1 polymorphism neither by the haplotype relative risk (HRR) method nor by the transmission disequilibrium test (TdT) method. The odds ratio for the DRD4 7-allele was 1.01 and 0.94 for both statistical tests, respectively, and the respective odds ratio for the DAT1 6-allele were 0.91 and 0.88.     

多巴胺D4受体基因和5-羟色胺转运体基因与注意缺陷多动障碍及其相关症状的关联分析

目的 探讨多巴胺D4受体(DRD4)基因和5-羟色胺转运体(5-HTT)基因与注意缺陷多动障碍(ADHD)及其相关症状的关系.方法利用Achenbach父母用儿童行为调查表评定139例ADHD患儿(患者组)的临床症状;采用聚合酶链反应、聚丙烯酰胺凝胶电泳结合银染技术,检测患者组和115名正常儿童(对照组)的基因型和等位基因频率.结果 (1)患者组与对照组间DRD4和5-HTT基因的基因型及等位基因频率分布的差异无统计学意义(P>0.05).(2)5-HTT基因的S/S基因型个体的社会退缩[(4.4±3.0)分]、躯体主诉[(3.6±2.7)分]得分高于S/L+L/L基因型个体[(3.3±2.6)分和(2.6±2.6)分],差异有统计学意义(P<0.05).(3)在非携带DRD4基因3等位基因个体中,S/L+L/L基因型的注意问题[(10.4±3.1)分]和社交问题[(7.2±3.7)分]得分高于S/S基因型个体[分别为(8.7±3.1)分和(5.3±2.3)分],差异有统计学意义(P<0.05).结论 DRD4基因和5-HTT基因与ADHD可能无关联;但5-HTT基因与ADHD的某些内化性症状可能存在关联;对ADHD的某些症状(注意问题和社交问题),DRD4基因与5-HTT可能存在相互协同作用.     

The dopamine transporter gene and the impulsivity phenotype in attention deficit hyperactivity disorder: a case-control association study in a Korean sample

The dopamine transporter gene (DAT1) has been extensively studied as one of the candidate genes in attention-deficit/hyperactivity disorder (ADHD). Several studies have reported on the association between the DAT1 10-repeat allele and cognitive variables in ADHD. However, few studies have been designed to ascertain the association between DAT1 genotypes other than the 10-repeat allele and cognitive endophenotypes in ADHD. The aim of this study was to examine the relationship between the DAT1 genotypes and the candidate endophenotypes, inattention and impulsivity symptoms, as measured by the continuous performance test (CPT), in a Korean sample of 85 children diagnosed with DSM-IV ADHD. Compared to the normal control group, the frequencies of the 9/10 genotype were significantly higher in the ADHD probands (χ² = 13.45, p = 0.02, OR = 4.12, 95% CI: 2.21–12.34) and parents of probands (χ² = 11.60, p = 0.03). The 9-repeat allele frequencies were significantly higher in the ADHD probands (χ² = 11.55, p = 0.03, OR = 4.43, 95% CI: 1.55–11.78) and parents of probands (χ² = 12.70, p = 0.03) than the normal control group. Compared to the ADHD probands without the 9-repeat allele (n = 74), the mean T-score, with regard to the commission errors of the CPT, was significantly higher (p < 0.05) in the ADHD probands with the 9-repeat allele (n = 11). Compared to the ADHD probands with other DAT1 genotypes, the mean T-score, with respect to the commission errors of the CPT, was significantly higher in the ADHD probands with the 9/10 genotype (p < 0.05). The results of this study suggest the possibility of an association between the DAT1 9-repeat allele and the impulsivity phenotype of ADHD.     

Schizotypy, attention deficit hyperactivity disorder, and dopamine genes

Previous research has suggested that there may be overlap between schizophrenia and attention-deficit hyperactivity disorder (ADHD). The relationship between schizotypal personality traits, ADHD features and polymorphisms was evaluated in dopamine-related genes. Thirty-one healthy, Caucasian men completed the Rust Inventory of Schizotypal Cognitions (RISC) and the ADHD Self-Report Scale (ASRS). Catechol-O-methyltransferase (COMT) Val158Met, dopamine receptors of the D3 type (DRD3) Ser9Gly, DRD4 variable number of tandem repeats (VNTR), and SLC6A3 VNTR polymorphisms were analyzed. RISC score was correlated with ASRS score (r = 0.54, P = 0.003). COMT Met homozygotes had higher ASRS scores than Val homozygotes (P = 0.005). These findings are consistent with evidence of overlap between schizophrenia and ADHD and support an involvement of COMT genotype in ADHD features.     

Sleep and sleep disorders in adults with attention deficit/hyperactivity disorder

Attention deficit/hyperactivity disorder (ADHD) is a frequent disorder that often persists in adulthood. Persistent ADHD is known to be a serious risk factor for other disorders in adulthood, and adults with ADHD often report on sleep disorders. Despite this, only few studies have investigated the subjective and objective quality of sleep in adults suffering from ADHD. Previous studies have revealed seriously impaired subjective sleep quality and increased nocturnal motor activity in spite of essentially normal standard polysomnographic parameters in this patient group. However, primary sleep disorders such as sleep apnea syndrome or restless legs syndrome (RLS) may be misdiagnosed as ADHD. Moreover, ADHD and primary sleep disorders may occur as comorbidities. In particular, RLS was suggested to be highly associated with ADHD, indicating a probable common central nervous dopaminergic dysfunction. To date, larger studies with adequate sample sizes that compare sleep in adult patients with ADHD, healthy control groups and patients with other primary sleep disorders are still lacking.     

Comorbidity of attention deficit hyperactivity disorder with conduct, depressive, anxiety, and other disorders

OBJECTIVE: Attention deficit hyperactivity disorder is a heterogeneous disorder of unknown etiology. Little is known about the comorbidity of this disorder with disorders other than conduct. Therefore, the authors made a systematic search of the psychiatric and psychological literature for empirical studies dealing with the comorbidity of attention deficit hyperactivity disorder with other disorders. DATA COLLECTION: The search terms included hyperactivity, hyperkinesis, attention deficit disorder, and attention deficit hyperactivity disorder, cross-referenced with antisocial disorder (aggression, conduct disorder, antisocial disorder), depression (depression, mania, depressive disorder, bipolar), anxiety (anxiety disorder, anxiety), learning problems (learning, learning disability, academic achievement), substance abuse (alcoholism, drug abuse), mental retardation, and Tourette's disorder. FINDINGS: The literature supports considerable comorbidity of attention deficit hyperactivity disorder with conduct disorder, oppositional defiant disorder, mood disorders, anxiety disorders, learning disabilities, and other disorders, such as mental retardation, Tourette's syndrome, and borderline personality disorder. CONCLUSIONS: Subgroups of children with attention deficit hyperactivity disorder might be delineated on the basis of the disorder's comorbidity with other disorders. These subgroups may have differing risk factors, clinical courses, and pharmacological responses. Thus, their proper identification may lead to refinements in preventive and treatment strategies. Investigation of these issues should help to clarify the etiology, course, and outcome of attention deficit hyperactivity disorder.     

Association between the dopamine transporter gene and the inattentive subtype of attention deficit hyperactivity disorder in Taiwan

Attention deficit hyperactivity disorder (ADHD) is a common heritable childhood psychiatric disorder. Since methylphenidate, one of the main drugs used to treat ADHD, targets the dopamine transporter, this study examined the linkage disequilibrium (LD) structure of the dopamine transporter gene (DAT1) and investigated whether the DAT1 gene was associated with ADHD. This Chinese family-based association sample consisted of 273 DSM-IV diagnosed ADHD probands and their family members (n = 906). We screened 15 polymorphisms across the DAT1 gene, including 14 single nucleotide polymorphism (SNP) markers and the variable number of tandem repeat (VNTR) polymorphism in 3′-untranslated region (3′UTR). Calculations of pairwise LD revealed three main haplotype blocks (HBs): HB1 (intron 2 through intron 6), HB2 (intron 8 through intron 11), and HB3 (3′UTR). Family-Based Association Tests showed that no allele was significantly more transmitted than expected to the ADHD children for these 15 markers. Haplotype-Based Association Tests showed that a haplotype rs27048 (C)/rs429699 (T) was significantly associated with the inattentive subtype (P = 0.008). In quantitative analyses, this haplotype also demonstrated significant association with the inattention severity (P = 0.012). Our finding of the haplotype rs27048 (C)/rs429699 (T) as a novel genetic marker in the inattentive ADHD subtype suggests that variation in the DAT1 gene may primarily affect the inattentive subtype of ADHD.     

No evidence of an association between norepinephrine transporter gene polymorphisms and attention deficit hyperactivity disorder: a family-based and case-control association study in a Korean sample

Neurobiological and pharmacological research has suggested that dysregulation of the central noradrenergic systems might be involved in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Previous studies have demonstrated that the norepinephrine transporter gene (SLC6A2) is associated with ADHD. The aims of this study were to examine the association of the SLC6A2 G1287A and -3081(A/T) polymorphisms with ADHD in Korean children and adolescents, and to determine the relationships of the genotypes of these two polymorphisms with continuous performance test results and the Junior Temperament and Character Inventory profiles of ADHD. In a case-control study, we assessed 186 ADHD probands and 150 normal controls; 109 trios were studied in a family-based association analysis. There were no significant differences in the genotype or allele frequencies of the SLC6A2 G1287A and -3081(A/T) polymorphisms between the ADHD and control groups (p > 0.05). In the transmission disequilibrium test analyses, there was no evidence for biased transmission of any of the alleles of the SLC6A2 G1287A and -3081(A/T) polymorphisms. In the haplotype analyses of these two polymorphisms, the global and individual chi(2) tests showed no significant associations between any of the haplotypes and ADHD. There were no significant differences with respect to the continuous performance test results and the Junior Temperament and Character Inventory profiles in the ADHD probands according to the genotypes of the SLC6A2 G1287A and -3081(A/T) polymorphisms. Our findings do not support SLC6A2 as a major genetic susceptibility factor in ADHD.     

Childhood attention deficit hyperactivity disorder features in adult mood disorders

A significant overlap between childhood mood disorders and many aspects of attention deficit hyperactivity disorder (ADHD) has been established. High rates of co-occurrence, familial aggregation, and more severe clinical manifestations of the illnesses when they are comorbid suggest that common genetic and environmental factors may contribute to the development of both disorders. Research on the co-occurrence of childhood ADHD and mood disorders in childhood has been conducted. We retrospectively investigated childhood ADHD features in adults with mood disorders. Childhood ADHD features were measured with the Korean version of the Wender Utah Rating Scale (WURS). The sample consisted of 1305 subjects: 108 subjects were diagnosed with bipolar disorder type I, 41 with bipolar disorder type II, 101 with major depressive disorder, and 1055 served as normal controls. We compared total WURS scores as well as scores on 3 factors (impulsivity, inattention, and mood instability and anxiety) among the 4 different diagnostic groups. The 4 groups differed significantly from one another on all scores. The group with bipolar disorder type II obtained the highest total scores on the WURS. The impulsivity and inattention associated with childhood ADHD were more significantly related to bipolar disorder type II than with bipolar disorder type I. The mood instability and anxiety associated with childhood ADHD seem to be significantly related to major depressive disorder in adulthood. In conclusion, multifactorial childhood ADHD features were associated with mood disorders of adulthood.     

How to differentiate bipolar disorder from attention deficit hyperactivity disorder and other common psychiatric disorders: A guide for clinicians

Bipolar disorder in children often is confused with attention deficit disorder, substance-induced mood disorder, oppositional defiant disorder, and conduct disorder. It is not uncommon for some of these disorders to be comorbid with pediatric bipolar disorder. This article provides the reader with a review of the existing literature on differentiating these illnesses and recognizing the phenomenology of each disorder as it pertains to a psychiatric diagnostic work-up of a child. Clinically helpful overlapping and unique characteristics of each disorder are discussed and a practical approach to differentiate these disorders is provided.     

How to differentiate bipolar disorder from attention deficit hyperactivity disorder and other common psychiatric disorders: A guide for clinicians

Bipolar disorder in children often is confused with attention deficit disorder, substance-induced mood disorder, oppositional defiant disorder, and conduct disorder. It is not uncommon for some of these disorders to be comorbid with pediatric bipolar disorder. This article provides the reader with a review of the existing literature on differentiating these illnesses and recognizing the phenomenology of each disorder as it pertains to a psychiatric diagnostic work-up of a child. Clinically helpful overlapping and unique characteristics of each disorder are discussed and a practical approach to differentiate these disorders is provided.