Differential Genetic Effect of the Norepinephrine Transporter Promoter Polymorphisms on Attention Problems in Clinical and Non-clinical Samples.
ABSTRACT: Among the monoaminergic modulatory neurotransmitters, norepinephrine is involved in task orienting, hence noradrenergic genetic variants have been studied in connection to attentional processes. The role of this catecholamine system is also highlighted by the selective norepinephrine transporter blocking atomoxetine, which has proved to be effective in the pharmacological treatment of Attention Deficit Hyperactivity Disorder (ADHD). In the present genetic association study three single nucleotide polymorphisms (rs28386840, rs2242446, rs3785143 SNPs) were analyzed from the 5' region of the norepinephrine transporter (NET, SLC6A2) gene, which have been linked to ADHD previously. Attention problems scores of the mother-rated Child Behavior Checklist (CBCL) were used in separate analyses of 88 preschoolers (59.1% male, 6 years of age) recruited from the general population and 120 child psychiatry patients with ADHD diagnosis (85.8% male, age: 9.8 ± 2.9). The NET SNPs showed associations with attention problems, but the direction was different in the two groups. Regarding the promoter variant rs28386840, which showed the most consistent association, the T-allele-carrier patients with ADHD had lower CBCL attention problems scores compared to patients with AA genotype (p = 0.023), whereas T-allele-carriers in the community sample had more attention problems (p = 0.042). Based on previous reports of lower NE levels in ADHD children and the inverted-U shape effect of NE on cognitive functions, we propose that rs28386840 (-3081) T-allele, which is associated with lower NET expression (and potentially higher synaptic NE level) would support attention processes among ADHD patients (similarly as atomoxetine increases NE levels), whereas it would hinder cortical functions in healthy children.
Project description:Cocaine abuse and attention deficit/hyperactivity disorder (ADHD) are often comorbid. Preclinical research indicates that medial prefrontal (mPFC) and orbitofrontal (OFC) cortices are important neural substrates for both disorders. Using the spontaneously hypertensive rat (SHR) model of ADHD, we reported that adolescent treatment with the stimulant methylphenidate, a dopamine (DAT) and norepinephrine (NET) transporter inhibitor, enhanced cocaine self-administration during adulthood, and was associated with increased DAT function in mPFC. This study investigates the effects of atomoxetine ((R)-N-methyl-?-(2-methylphenoxy)-benzenepropanamine hydrochloride) treatment, a selective NET inhibitor, during adolescence on cocaine self-administration and on DAT function and cell-surface expression in mPFC and OFC during adulthood. SHR acquired cocaine self-administration faster than Wistar-Kyoto and Wistar. Across cocaine doses, SHR earned more cocaine infusions and had higher progressive-ratio breakpoints than Wistar-Kyoto and Wistar, demonstrating that the SHR phenotype models comorbid ADHD and cocaine abuse. Prior atomoxetine treatment did not augment cocaine self-administration in SHR, but acquisition was enhanced in Wistar-Kyoto. No strain differences were found for DAT kinetic parameters or cellular localization in the vehicle controls. Atomoxetine did not alter DAT kinetic parameters or localization in SHR mPFC. Rather, atomoxetine decreased V(max) and DAT cell surface expression in SHR OFC, indicating that inhibition of NET by atomoxetine treatment during adolescence indirectly reduced DAT function and trafficking to the cell surface in OFC, specifically in the ADHD model. Thus, atomoxetine, unlike methylphenidate, does not enhance vulnerability to cocaine abuse in SHR and may represent an important alternative for teens with ADHD when drug addiction is a concern.
Project description:Attention deficit hyperactivity disorder (ADHD) is a heterogeneous disorder with a strong genetic component. The norepinephrine transporter (NET) is a key target for ADHD treatment and the NET gene has been of high interest as a possible modulator of ADHD pathophysiology. Therefore, we conducted an imaging genetics study to examine possible effects of single nucleotide polymorphisms (SNPs) within the NET gene on NET nondisplaceable binding potential (BPND ) in patients with ADHD and healthy controls (HCs). Twenty adult patients with ADHD and 20 HCs underwent (S,S)-[18F]FMeNER-D2 positron emission tomography (PET) and were genotyped on a MassARRAY MALDI-TOF platform using the Sequenom iPLEX assay. Linear mixed models analyses revealed a genotype-dependent difference in NET BPND between groups in the thalamus and cerebellum. In the thalamus, a functional promoter SNP (-3081 A/T) and a 5'-untranslated region (5'UTR) SNP (-182 T/C), showed higher binding in ADHD patients compared to HCs depending on the major allele. Furthermore, we detected an effect of genotype in HCs, with major allele carriers having lower binding. In contrast, for two 3'UTR SNPs (*269 T/C, *417 A/T), ADHD subjects had lower binding in the cerebellum compared to HCs depending on the major allele. Additionally, symptoms of hyperactivity and impulsivity correlated with NET BPND in the cerebellum depending on genotype. Symptoms correlated positively with cerebellar NET BPND for the major allele, while symptoms correlated negatively to NET BPND in minor allele carriers. Our findings support the role of genetic influence of the NE system on NET binding to be pertubated in ADHD.
Project description:Attention deficit hyperactivity disorder (ADHD) is associated with hypofunctional medial prefrontal cortex (mPFC) and orbitofrontal cortex (OFC). Methylphenidate (MPH) remediates ADHD, in part, by inhibiting the norepinephrine transporter (NET). MPH also reduces ADHD-like symptoms in spontaneously hypertensive rats (SHRs), a model of ADHD. However, effects of chronic MPH treatment on NET function in mPFC and OFC in SHR have not been reported. In the current study, long-term effects of repeated treatment with a therapeutically relevant oral dose of MPH during adolescence on NET function in subregions of mPFC (cingulate gyrus, prelimbic cortex and infralimbic cortex) and in the OFC of adult SHR, Wistar-Kyoto (WKY, inbred control) and Wistar (WIS, outbred control) rats were determined using in vivo voltammetry. Following local ejection of norepinephrine (NE), uptake rate was determined as peak amplitude (Amax)× first-order rate constant (k-1). In mPFC subregions, no strain or treatment effects were found in NE uptake rate. In OFC, NE uptake rate in vehicle-treated adult SHR was greater than in adult WKY and WIS administered vehicle. MPH treatment during adolescence normalized NE uptake rate in OFC in SHR. Thus, the current study implicates increased NET function in OFC as an underlying mechanism for reduced noradrenergic transmission in OFC, and consequently, the behavioral deficits associated with ADHD. MPH treatment during adolescence normalized NET function in OFC in adulthood, suggesting that the therapeutic action of MPH persists long after treatment cessation and may contribute to lasting reductions in deficits associated with ADHD.
Project description:Atomoxetine is the most widely used nonstimulant for the treatment of attention-deficit/hyperactivity disorder (ADHD). It selectively acts on the norepinephrine (NE) system. Dopamine beta hydroxylase (DBH) regulates the synthesis of NE. This study aimed to investigate whether variants in the DBH gene have an effect on the differential response to atomoxetine.Children and adolescents with ADHD were enrolled in a prospective, open-label study of atomoxetine for 8-12 weeks. The dose was titrated to 1.2-1.4?mg/kg per day and maintained for at least 4 weeks. The primary efficacy measure was the investigator-rated ADHD Rating Scale-IV (ADHD-RS-IV). Three categorical evaluations of treatment effects (defined as response, robust response, and remission) were used. We used a candidate gene approach. Eight single nucleotide polymorphisms (SNPs) in DBH were selected and genotyped based on the functional annotation in literature. Their association with response or remission status was analyzed.Four SNPs were found nominally associated with response status (rs1076150, p?=?0.0484; rs2873804, p?=?0.0348; rs1548364, p?=?0.0383; and rs2519154, p?=?0.0097), two were associated with robust response (rs1076150, p?=?0.0349; and rs2519154, p?=?0.0047), and one was associated with remission (rs2519154, p?=?0.0479). The association between rs2519154 and robust response was significant after correction of multiple comparison (p?=?0.0384). Two haplotypes of linkage disequilibrium (LD) block1 (constituted by rs1108580, rs2873804, rs1548364, and rs2519154) were nominally associated with response and robust response status (CTAC: p?=?0.0301 for response, p?=?0.0374 for robust response; TCGT: p?=?0.0317 for response, p?=?0.021 for robust response), whereas one haplotype (GC) of LD block2 (constituted by rs2073837 and rs129882) was associated with robust response and remission status (p?=?0.0377 for robust response; p?=?0.0321 for remission), although none achieved significant threshold after multiple comparison.Variants in DBH genes were associated with atomoxetine response in the treatment of ADHD. Further replication in larger samples would be warranted.
Project description:Attention-deficit/hyperactivity disorder (ADHD) is the most frequently diagnosed neurodevelopmental disorder. The norepinephrine transporter (NET) inhibitor atomoxetine, the first nonstimulant drug licensed for ADHD treatment, also acts as an N-methyl-D-aspartate receptor (NMDAR) antagonist. The compound's effects on gene expression and protein levels of NET and NMDAR subunits (1, 2A, and 2B) are unknown. Therefore, adolescent Sprague Dawley rats were treated with atomoxetine (3 mg/kg, intraperitoneal injection [i.p.]) or saline (0.9%, i.p.) for 21 consecutive days on postnatal days (PND) 21-41. In humans, atomoxetine's earliest clinical therapeutic effects emerge after 2-3 weeks. Material from prefrontal cortex, striatum (STR), mesencephalon (MES), and hippocampus (HC) was analyzed either directly after treatment (PND 42) or 2 months after termination of treatment (PND 101) to assess the compound's long-term effects. In rat brains analyzed immediately after treatment, protein analysis exhibited decreased levels of the NET in HC, and NMDAR subunit 2B in both STR and HC; the transcript levels were unaltered. In rat brains probed 2 months after final atomoxetine exposure, messenger RNA analysis also revealed significantly reduced levels of genes coding for NMDAR subunits in MES and STR. NMDAR protein levels were reduced in STR and HC. Furthermore, the levels of two SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, synaptophysin and synaptosomal-associated protein 25, were also significantly altered in both treatment groups. This in vivo study detected atomoxetine's effects beyond NET inhibition. Taken together, these data reveal that atomoxetine seems to decrease glutamatergic transmission in a brain region-specific manner. Long-term data show that the compound's impact is not due to an acute pharmacological effect but lasts or even amplifies after a drug-free period of 2 months, leading to altered development of synaptic composition. These alterations might contribute to atomoxetine's clinical effects in the treatment of ADHD, a neurodevelopmental disorder in which synaptic processes and especially a dysregulated glutamatergic metabolism seem to be involved.
Project description:Attention-deficit hyperactivity disorder (ADHD) is a highly heritable disorder of impaired behavioral inhibition, increased motor activity, and inattention. The norepinephrine transporter (NET, SLC6A2) represents an important candidate gene for contribution to ADHD because it regulates catecholamine extracellular and tissue concentrations and contributes to executive functions disrupted in ADHD, and NET is a target for most effective ADHD therapeutics. We identified four NET coding single nucleotide polymorphisms (SNPs) in two ADHD sample sets; two SNPs produce protein variants (T283M, V245I), one of which, T283M, is a novel variant. Examination of the maternal family members through whom the T283M mutation was transmitted, provided no additional ADHD diagnoses. Given the previous identification of a NET mutation that contributes to a familial tachycardia syndrome, we examined autonomic function to reveal in the proband the highest standing-induced increase in heart rate among the ADHD subjects examined. We measured [3H]NE and [3H]dopamine transport for T283M, V245I, and a previously identified NET variant, T283R. T283M and V245I demonstrated decreased substrate transport, as did T283R, suggesting that the T283 residue is sensitive to mutation. Identification of polymorphic sites within NET, specifically those that produce functional consequences, is one critical step in elucidating the genetic variation contributing to the heritable component of diseases such as ADHD.
Project description:This study examined prevalence of psychiatric disorders and behavioral problems in children with and without prenatal alcohol exposure (AE) and attention-deficit/hyperactivity disorder (ADHD).Primary caregivers of 344 children (8 to 16 years, M = 12.28) completed the Computerized Diagnostic Interview Schedule for Children-IV (C-DISC-4.0) and the Child Behavior Checklist (CBCL). Subjects comprised 4 groups: AE with ADHD (AE+, n = 85) and without ADHD (AE-, n = 52), and nonexposed with ADHD (ADHD, n = 74) and without ADHD (CON, n = 133). The frequency of specific psychiatric disorders, number of psychiatric disorders (comorbidity), and CBCL behavioral scores were examined using chi-square and analysis of covariance techniques.Clinical groups had greater frequency of all psychiatric disorders, except for anxiety, where the AE- and CON groups did not differ. There was a combined effect of AE and ADHD on conduct disorder. For comorbidity, children with ADHD had increased psychiatric disorders regardless of AE, which did not have an independent effect on comorbidity. For CBCL scores, there were significant main effects of AE and ADHD on all scores and significant AE × ADHD interactions for Withdrawn/Depressed, Somatic Complaints, Attention, and all Summary scores. There was a combined effect of AE and ADHD on Externalizing, Total Problems, and Attention Problems.Findings indicate that ADHD diagnosis elevates children's risk of psychiatric diagnoses, regardless of AE, but suggest an exacerbated relation between AE and ADHD on conduct disorder and externalizing behavioral problems in children. Findings affirm a poorer behavioral prognosis for alcohol-exposed children with ADHD and suggest that more than 1 neurobehavioral profile may exist for individuals with AE.
Project description:BACKGROUND:Ketamine is receiving increasing attention as a rapid-onset antidepressant in patients suffering from major depressive disorder (MDD) with treatment resistance or severe suicidal ideation. Ketamine modulates several neurotransmitter systems, including norepinephrine via the norepinephrine transporter (NET), both peripherally and centrally. The locus coeruleus (LC), which has high NET concentration, has been attributed to brain networks involved in depression. Thus we investigated the effects of single-dose of racemic ketamine on the LC using resting state functional MRI. METHODS:Fifty-nine healthy participants (mean age 25.57?±?4.72) were examined in a double-blind, randomized, placebo-controlled study with 7 Tesla MRI. We investigated the resting state functional connectivity (rs-fc) of the LC before and one hour after subanesthetic ketamine injection (0.5?mg/kg), as well as associations between its rs-fc and a common polymorphism in the NET gene (rs28386840). RESULTS:A significant interaction of drug and time was revealed, and post hoc testing showed decreased rs-fc between LC and the thalamus after ketamine administration compared with baseline levels, including the mediodorsal, ventral anterior, ventral lateral, ventral posterolateral and centromedian nuclei. The rs-fc reduction was more pronounced in NET rs28386840 [AA] homozygous subjects than in [T] carriers. CONCLUSIONS:We demonstrated acute rs-fc changes after ketamine administration in the central node of the norepinephrine pathway. These findings may contribute to understanding the antidepressant effect of ketamine at the system level, supporting modes of action on networks subserving aberrant arousal regulation in depression.
Project description:A potentially useful tool for understanding the distribution and determinants of emotional dysregulation in children is a Child Behavior Checklist profile, comprising the Attention Problems, Anxious/Depressed, and Aggressive Behavior clinical subscales (CBCL-DP). The CBCL-DP indexes a heritable trait that increases susceptibility for later psychopathology, including severe mood problems and aggressive behavior. We have conducted a genome-wide association study of the CBCL-DP in children with attention-deficit/hyperactivity disorder (ADHD).Families were ascertained at Massachusetts General Hospital and University of California, Los Angeles. Genotyping was conducted with the Illumina Human1M or Human1M-Duo BeadChip platforms. Genome-wide association analyses were conducted with the MQFAM multivariate extension of PLINK.CBCL data were available for 341 ADHD offspring from 339 ADHD affected trio families from the UCLA (N = 128) and the MGH (N = 213) sites. We found no genome-wide statistically significant associations but identified several plausible candidate genes among findings at p < 5E-05: TMEM132D, LRRC7, SEMA3A, ALK, and STIP1.We found suggestive evidence for developmentally expressed genes operant in hippocampal dependent memory and learning with the CBCL-DP.
Project description:Pharmacologic and animal studies have strongly implicated the norepinephrine transporter (NET) in the pathophysiology of attention-deficit/hyperactivity disorder (ADHD). We conducted a family-based study, with stratification based on sex and subtype, to test the association between 30 tag single-nucleotide polymorphisms (SNPs) within the gene encoding NET (SLC6A2) and ADHD.Family-based association tests were conducted with the categorical diagnosis of ADHD, as well as quantitative phenotypes of clinical relevance (Conners Global Index for Teachers and Parents, and Child Behavior Checklist measures). Sliding window haplotype analysis was conducted with screening based on conditional power using PBAT.A previously reported association with rs3785143 was confirmed in this study. Further, extensive association was observed with haplotype blocks, with a differential pattern observed based on sex and subtype. The 5' region of the gene (encompassing haplotype block 1 and including a functional promoter SNP, rs28386840) showed an association with ADHD in girls (irrespective of subtype). A different region of the gene (distributed around haplo-type block 2) was associated with distinct behavioural phenotypes in boys. These findings are correlated with previously reported functional studies of gene variants in SLC6A2.The most important limitation of the study is the small size of the groups resulting from the stratification based on sex followed by subtype.The results obtained in this family-based study suggest that haplotype blocks within different regions of SLC6A2 show differential association with the disorder based on sex and subtype. These associations may have been masked in previous studies when tests were conducted with pooled samples.