Andrea Boreatti-Hümmer

Multicenter Analysis of the SLC6A3/DAT1 VNTR Haplotype in Persistent ADHD Suggests Differential Involvement of the Gene in Childhood and Persistent ADHD

Attention deficit/hyperactivity disorder (ADHD) is one of the most common neuropsychiatric disorders with a worldwide prevalence around 4–5% in children and 1–4% in adults. Although ADHD is highly heritable and familial risk may contribute most strongly to the persistent form of the disorder, there are few studies on the genetics of ADHD in adults. In this paper, we present the first results of the International Multicentre Persistent ADHD Genetics CollaboraTion (IMpACT) that has been set up with the goal of performing research into the genetics of persistent ADHD. In this study, we carried out a combined analysis as well as a meta-analysis of the association of the SLC6A3/DAT1 gene with persistent ADHD in 1440 patients and 1769 controls from IMpACT and an earlier report. DAT1, encoding the dopamine transporter, is one of the most frequently studied genes in ADHD, though results have been inconsistent. A variable number tandem repeat polymorphism (VNTR) in the 3′-untranslated region (UTR) of the gene and, more recently, a haplotype of this VNTR with another VNTR in intron 8 have been the target of most studies. Although the 10/10 genotype of the 3′-UTR VNTR and the 10-6 haplotype of the two VNTRs are thought to be risk factors for ADHD in children, we found the 9/9 genotype and the 9-6 haplotype associated with persistent ADHD. In conclusion, a differential association of DAT1 with ADHD in children and in adults might help explain the inconsistencies observed in earlier association studies. However, the data might also imply that DAT1 has a modulatory rather than causative role in ADHD.

Genome-wide copy number variation analysis in attention-deficit/hyperactivity disorder: association with neuropeptide Y gene dosage in an extended pedigree

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurodevelopmental syndrome characterized by hyperactivity, inattention and increased impulsivity. To detect micro-deletions and micro-duplications that may have a role in the pathogenesis of ADHD, we carried out a genome-wide screen for copy number variations (CNVs) in a cohort of 99 children and adolescents with severe ADHD. Using high-resolution array comparative genomic hybridization (aCGH), a total of 17 potentially syndrome-associated CNVs were identified. The aberrations comprise 4 deletions and 13 duplications with approximate sizes ranging from 110 kb to 3 Mb. Two CNVs occurred de novo and nine were inherited from a parent with ADHD, whereas five are transmitted by an unaffected parent. Candidates include genes expressing acetylcholine-metabolizing butyrylcholinesterase (BCHE), contained in a de novo chromosome 3q26.1 deletion, and a brain-specific pleckstrin homology domain-containing protein (PLEKHB1), with an established function in primary sensory neurons, in two siblings carrying a 11q13.4 duplication inherited from their affected mother. Other genes potentially influencing ADHD-related psychopathology and involved in aberrations inherited from affected parents are the genes for the mitochondrial NADH dehydrogenase 1 α subcomplex assembly factor 2 (NDUFAF2), the brain-specific phosphodiesterase 4D isoform 6 (PDE4D6) and the neuronal glucose transporter 3 (SLC2A3). The gene encoding neuropeptide Y (NPY) was included in a ∼3 Mb duplication on chromosome 7p15.2-15.3, and investigation of additional family members showed a nominally significant association of this 7p15 duplication with increased NPY plasma concentrations (empirical family-based association test, P=0.023). Lower activation of the left ventral striatum and left posterior insula during anticipation of large rewards or losses elicited by functional magnetic resonance imaging links gene dose-dependent increases in NPY to reward and emotion processing in duplication carriers. These findings implicate CNVs of behaviour-related genes in the pathogenesis of ADHD and are consistent with the notion that both frequent and rare variants influence the development of this common multifactorial syndrome.

Cross-disorder analysis of bipolar risk genes: further evidence of DGKH as a risk gene for bipolar disorder, but also unipolar depression and adult ADHD.

Recently, several genome-wide association studies (GWAS) on bipolar disorder (BPD) suggested novel risk genes. However, only few of them were followed up and further, the specificity of these genes is even more elusive. To address these issues, we genotyped SNPs in ANK3, CACNA1C, CMTM8, DGKH, EGFR, and NPAS3, which were significantly associated with BPD in previous GWAS, in a sample of 380 BPD patients. Replicated SNPs were then followed up in patients suffering from unipolar depression (UPD; n=387) or adult attention-deficit/hyperactivity disorder (aADHD; n=535). While we could not confirm an association of ANK3, CACNA1C, and EGFR with BPD, 10 SNPs in DGKH, CMTM8, and NPAS3 were nominally associated with disease, with two DGKH markers surviving correction for multiple testing. When these were followed up in UPD and aADHD, seven DGKH SNPs were also associated with UPD, while one SNP each in NPAS3 and CMTM8 and four in DGKH were linked to aADHD. Furthermore, a DGKH haplotype consisting of rs994856/rs9525580/rs9525584 GAT was associated with all disorders tested, while the complementary AGC haplotype was protective. The corresponding haploblock spans a 27-kb region covering exons coding for amino acids 65–243, and thus might include functional variants yet to be identified. We demonstrate an association of DGKH with BPD, UPD, and aADHD by applying a two-stage design. These disorders share the feature of mood instability, so that this phenotype might be associated with genetic variation in DGKH.

Meta‐analysis of brain‐derived neurotrophic factor p.Val66Met in adult ADHD in four European populations

Attention‐deficit hyperactivity disorder (ADHD) is a multifactorial, neurodevelopmental disorder that often persists into adolescence and adulthood and is characterized by inattention, hyperactivity and impulsiveness. Before the advent of the first genome‐wide association studies in ADHD, genetic research had mainly focused on candidate genes related to the dopaminergic and serotoninergic systems, although several other genes had also been assessed. Pharmacological data, analysis of animal models and association studies suggest that Brain‐Derived Neurotrophic Factor (BDNF) is also a strong candidate gene for ADHD. Several polymorphisms in BDNF have been reported and studied in psychiatric disorders but the most frequent is the p.Val66Met (rs6265G > A) single nucleotide polymorphism (SNP), with functional effects on the intracellular trafficking and secretion of the protein. To deal with the inconsistency raised among different case–control and family‐based association studies regarding the p.Val66Met contribution to ADHD, we performed a meta‐analysis of published as well as unpublished data from four different centers that are part of the International Multicentre Persistent ADHD CollaboraTion (IMpACT). A total of 1,445 adulthood ADHD patients and 2,247 sex‐matched controls were available for the study. No association between the p.Val66Met polymorphism and ADHD was found in any of the four populations or in the pooled sample. The meta‐analysis also showed that the overall gene effect for ADHD was not statistically significant when gender or comorbidity with mood disorders were considered. Despite the potential role of BDNF in ADHD, our data do not support the involvement of p.Val66Met in the pathogenesis of this neuropsychiatric disorder.

Diminished prefrontal oxygenation with normal and above-average verbal fluency performance in adult ADHD

Attention-Deficit/Hyperactivity Disorder (ADHD) in adults is associated with deficits in executive functions such as verbal fluency. Functional near-infrared spectroscopy offers the possibility to measure brain activity during verbal fluency in psychiatric patients due to low susceptibility to movements artefacts. Fourteen patients with mainly combined ADHD subtype and 14 healthy controls matched for age, gender, handedness, education level, and intelligence showed equal performance in phonological verbal fluency and higher performance in semantical verbal fluency in comparison to the controls. On the level of brain function indicated by concentration changes of oxygenated and deoxygenated haemoglobin, both groups showed inferior frontal brain activity during both tasks. ADHD patients had a lower magnitude of oxygenation and a significant negative correlation of brain activity with performance, i.e. higher brain activity was associated with lower performance. These results might be interpreted as a lack of disease related deficits, as an economical recruitment of cognitive resources, or - more likely - as an expression of a benefit in the patient group. High verbal competence in our samples could contribute to these findings. One speculative and post hoc explanation aims at the clinically well-known phenomenon of hyperfocusing in patients with ADHD.

An international multicenter association study of the serotonin transporter gene in persistent ADHD.

Attention deficit hyperactivity disorder (ADHD) is a common behavioral disorder affecting children and adults. It has been suggested that gene variants related to serotonin neurotransmission are associated with ADHD. We tested the functional promoter polymorphism 5‐HTTLPR and seven single nucleotide polymorphisms in SLC6A4 for association with ADHD in 448 adult ADHD patients and 580 controls from Norway. Replication attempts were performed in a sample of 1454 Caucasian adult ADHD patients and 1302 controls from Germany, Spain, the Netherlands and USA, and a meta‐analysis was performed also including a previously published adult ADHD study. We found an association between ADHD and rs140700 [odds ratio (OR ) = 0.67; P = 0.01] and the short (S) allele of the 5‐HTTLPR (OR = 1.19; P = 0.06) in the Norwegian sample. Analysis of a possible gender effect suggested that the association might be restricted to females (rs140700: OR = 0.45; P = 0.00084). However, the meta‐analysis of 1894 cases and 1878 controls could not confirm the association for rs140700 [OR = 0.85, 95% confidence interval (CI) = 0.67–1.09; P = 0.20]. For 5‐HTTLPR, five of six samples showed a slight overrepresentation of the S allele in patients, but meta‐analysis refuted a strong effect (OR = 1.10, 95% CI = 1.00–1.21; P = 0.06). Neither marker showed any evidence of differential effects for ADHD subtype, gender or symptoms of depression/anxiety. In conclusion, our results do not support a major role for SLC6A4 common variants in persistent ADHD, although a modest effect of the 5‐HTTLPR and a role for rare variants cannot be excluded.

Abnormal affective responsiveness in attention-deficit/hyperactivity disorder: subtype differences.

BACKGROUND Emotional-motivational dysfunctions likely contribute to attention-deficit/hyperactivity disorder (ADHD), especially to hyperactive and impulsive symptoms. This study examined the affective modulation of the startle reflex in a large sample of ADHD patients. The aim was to compare subtypes of ADHD. METHODS One hundred ninety-seven unmedicated adult ADHD patients (127 combined type [ADHD-C]; 50 inattentive type [ADHD-I]; 20 hyperactive-impulsive type [ADHD-HI]) and 128 healthy control subjects were examined. The affect-modulated startle response as well as valence and arousal ratings were assessed for pleasant, neutral, and unpleasant picture stimuli. RESULTS Control subjects exhibited startle response attenuation and potentiation by pleasant and unpleasant pictures, respectively. In ADHD-HI, startle response was not attenuated by pleasant and not potentiated by unpleasant stimuli. In ADHD-C, startle response was not attenuated by pleasant pictures, and ADHD-I responded similar to control subjects but startle response was attenuated to a lesser degree by pleasant stimuli. The ADHD-HI group rated all pictures as more positive, and male ADHD-HI rated unpleasant stimuli as less arousing. CONCLUSIONS This is the first study to assess the affect-modulated startle response in ADHD. It confirms emotional dysfunctions in these patients; all subtypes showed more or less diminished emotional reactions to pleasant stimuli. The hyperactive-impulsive type was also marked by blunted reactions to unpleasant stimuli. Results suggest that response patterns to emotional cues or reward may help to differentiate ADHD subtypes. Blunted emotional reactivity is especially pronounced in ADHD patients with symptoms of hyperactivity and impulsivity (ADHD-C, ADHD-HI).

Neural correlates of performance monitoring in adult patients with attention deficit hyperactivity disorder (ADHD).

INTRODUCTION In this study, the neural correlates of error processing in adult patients with attention deficit hyperactivity disorder (ADHD) are to be investigated for the first time. Recent studies in children with ADHD suggested, with some inconsistencies, deficits in error processing. Based on an analogue study with students, we hypothesized that ADHD patients show reduced amplitudes in the event-related potential (ERP) of the Pe (error positivity) but normal amplitudes of the ERN (error-related negativity) after incorrect responses. METHOD In this study we investigated 34 adult ADHD patients and 34 healthy controls with a modified version of the Eriksen flanker task while recording the neural activity with 26 scalp EEG electrodes. Patients discontinued all medication at least 3 days prior to investigation. Age was included as a control variable for the statistical analyses. RESULTS AND CONCLUSION As hypothesized, we found reduced Pe amplitudes, but also reduced ERN values, in ADHD patients. Importantly, theses differences as well as the deficits in behavioural performance were mainly detectable in the younger subsample, but not in the elderly subsample. Our results indicate that adult ADHD patients are characterized by deficits in error processing, which vanish with age.

Dopamine transporter (SLC6A3) genotype impacts neurophysiological correlates of cognitive response control in an adult sample of patients with ADHD.

Studies provide ample evidence for a dysfunction in dopaminergic neurotransmission in Attention-Deficit/Hyperactivity Disorder (ADHD). In that respect, a common variable number of tandem repeats (VNTR) polymorphism in the 3′ untranslated region (UTR) of the dopamine transporter gene (SLC6A3) has been repeatedly associated with the disorder. Here, we examined the influence of the common 9- and 10-repeat alleles of SLC6A3 on prefrontal brain functioning and cognitive response control in a large sample of adult ADHD patients (n=161) and healthy controls (n=109). To this end, we inspected a neurophysiological marker of cognitive response control (NoGo anteriorization, NGA) elicited by means of a Go-NoGo task (continuous performance test, CPT). Within the group of ADHD patients, nine-repeat allele carriers showed significantly reduced NGA, whereas no influence of SLC6A3 genotype was observed in the control group. In contrast to previous association studies of children, the nine-repeat—not the 10-repeat—allele was associated with functional impairments in our sample of adult ADHD patients. Our findings confirm a significant effect of the SLC6A3 genotype on the neurophysiological correlates of cognitive response control in ADHD, and indicate that still to-be-identified age-related factors are important variables modulating the effect of genetic factors on endophenotypes.

Working memory and response inhibition as one integral phenotype of adult ADHD? A behavioral and imaging correlational investigation.

Objective: It is an open question whether working memory (WM) and response inhibition (RI) constitute one integral phenotype in attention deficit hyperactivity disorder (ADHD). Method: The authors investigated 45 adult ADHD patients and 41 controls comparable for age, gender, intelligence, and education during a letter n-back and a stop-signal task, and measured prefrontal oxygenation by means of functional near-infrared spectroscopy. Results: The authors replicated behavioral and cortical activation deficits in patients compared with controls for both tasks and also for performance in both control conditions. In the patient group, 2-back performance was correlated with stop-signal reaction time. This correlation did not seem to be specific for WM and RI as 1-back performance was correlated with go reaction time. No significant correlations of prefrontal oxygenation between WM and RI were found. Conclusion: The authors’ findings do not support the hypothesis of WM and RI representing one integral phenotype of ADHD mediated by the prefrontal cortex.