Absence of association with DAT1 polymorphism and response to methylphenidate in a sample of adults with ADHD

Biological Predictors of Treatment Response in Adult Attention Deficit Hyperactivity Disorder (ADHD): A Systematic Review

Background: Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent condition with onset in childhood and in many cases persisting into adulthood. Even though an increasing number of studies have investigated the efficacy of pharmacotherapy in the management of adult ADHD, few authors have tried to identify the biological predictors of treatment response. Objectives: To summarize the available data about the biological markers of treatment response in adults affected by ADHD. Methods: A search on the main biomedical and psychological archives (PubMed, Embase, Scopus, and PsycINFO) was performed. Manuscripts in English, published up to May 2022 and having the biological predictors of treatment response in adults with ADHD as their main topic, were included. Results: A total of 3855 articles was screened. Twenty-two articles were finally included. Most of the manuscripts studied neuroimaging and electrophysiological factors as potential predictors of treatment response in adult ADHD patients. No reliable markers were identified until now. Promising findings on this topic regard genetic polymorphisms in snap receptor (SNARE) proteins and default mode network-striatum connectivity. Conclusions: Even though some biological markers seem promising for the prediction of treatment response in adults affected by ADHD, further studies are needed to confirm the available data in the context of precision medicine.

Genetics in the ADHD Clinic: How Can Genetic Testing Support the Current Clinical Practice?

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder with a childhood prevalence of 5%. In about two-thirds of the cases, ADHD symptoms persist into adulthood and often cause significant functional impairment. Based on the results of family and twin studies, the estimated heritability of ADHD approximates 80%, suggests a significant genetic component in the etiological background of the disorder; however, the potential genetic effects on disease risk, symptom severity, and persistence are unclear. This article provides a brief review of the genome-wide and candidate gene association studies with a focus on the clinical aspects, summarizing findings of ADHD disease risk, ADHD core symptoms as dimensional traits, and other traits frequently associated with ADHD, which may contribute to the susceptibility to other comorbid psychiatric disorders. Furthermore, neuropsychological impairment and measures from neuroimaging and electrophysiological paradigms, emerging as potential biomarkers, also provide a prominent target for molecular genetic studies, since they lie in the pathway from genes to behavior; therefore, they can contribute to the understanding of the underlying neurobiological mechanisms and the interindividual heterogeneity of clinical symptoms. Beyond the aforementioned aspects, throughout the review, we also give a brief summary of the genetic results, including polygenic risk scores that can potentially predict individual response to different treatment options and may offer a possibility for personalized treatment for the therapy of ADHD in the future.

Extended-release methylphenidate for attention deficit hyperactivity disorder (ADHD) in adults

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a psychiatric diagnosis increasingly used in adults. The recommended first-line pharmacological treatment is central nervous system (CNS) stimulants, such as methylphenidate, but uncertainty remains about its benefits and harms.

OBJECTIVES

To assess the beneficial and harmful effects of extended-release formulations of methylphenidate in adults diagnosed with ADHD.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, nine other databases and four clinical trial registries up to February 2021. We searched 12 drug regulatory databases for clinical trial data up to 13 May 2020. In addition, we cross-referenced all available trial identifiers, handsearched reference lists, searched pharmaceutical company databases, and contacted trial authors.

SELECTION CRITERIA

Randomised, double-blind, parallel-group trials comparing extended-release methylphenidate formulations at any dose versus placebo and other ADHD medications in adults diagnosed with ADHD.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data. We assessed dichotomous outcomes as risk ratios (RRs), and rating scales and continuous outcomes as mean differences (MDs) or standardised mean differences (SMDs). We used the Cochrane risk of bias tool to assess risks of bias, and GRADE to assess the certainty of the evidence. We meta-analysed the data using a random-effects model. We assessed three design characteristics that may impair the trial results' 'generalisability'; exclusion of participants with psychiatric comorbidity; responder selection based on previous experience with CNS stimulants; and risk of withdrawal effects. Our prespecified primary outcomes were functional outcomes, self-rated ADHD symptoms, and serious adverse events. Our secondary outcomes included quality of life, ADHD symptoms rated by investigators and by peers such as family members, cardiovascular variables, severe psychiatric adverse events, and other adverse events.

MAIN RESULTS

We included 24 trials (5066 participants), of which 21 reported outcome data for this review. We also identified one ongoing study. We included documents from six drug regulatory agencies covering eight trials. Twenty-one trials had an outpatient setting and three were conducted in prisons. They were primarily conducted in North America and Europe. The median participant age was 36 years. Twelve trials (76% of participants) were industry-sponsored, four (14% of participants) were publicly funded with industry involvement, seven (10% of participants) were publicly funded, and one had unclear funding. The median trial duration was eight weeks. One trial was rated at overall unclear risk of bias and 20 trials were rated at overall high risk of bias, primarily due to unclear blinding of participants and investigators, attrition bias, and selective outcome reporting. All trials were impaired in at least one of the three design characteristics related to 'generalisability'; for example, they excluded participants with psychiatric comorbidity such as depression or anxiety, or included participants only with a previous positive response to methylphenidate, or similar drugs. This may limit the trials' usefulness for clinical practice, as they may overestimate the benefits and underestimate the harms. Extended-release methylphenidate versus placebo (up to 26 weeks) For the primary outcomes, we found very low-certainty evidence that methylphenidate had no effect on 'days missed at work' at 13-week follow-up (mean difference (MD) -0.15 days, 95% confidence interval (CI) -2.11 to 1.81; 1 trial, 409 participants) or serious adverse events (risk ratio (RR) 1.43, CI 95% CI 0.85 to 2.43; 14 trials, 4078 participants), whereas methylphenidate improved self-rated ADHD symptoms (small-to-moderate effect; SMD -0.37, 95% CI -0.43 to -0.30; 16 trials, 3799 participants). For secondary outcomes, we found very low-certainty evidence that methylphenidate improved self-rated quality of life (small effect; SMD -0.15, 95% CI -0.25 to -0.05; 6 trials, 1888 participants), investigator-rated ADHD symptoms (small-to-moderate effect; SMD -0.42, 95% CI -0.49 to -0.36; 18 trials, 4183 participants), ADHD symptoms rated by peers such as family members (small-to-moderate effect; SMD -0.31, 95% CI -0.48 to -0.14; 3 trials, 1005 participants), and increased the risk of experiencing any adverse event (RR 1.27, 95% CI 1.19 to 1.37; 14 trials, 4214 participants). We rated the certainty of the evidence as 'very low' for all outcomes, primarily due to high risk of bias and 'indirectness of the evidence'. One trial (419 participants) had follow-up at 52 weeks and two trials (314 participants) included active comparators, hence long-term and comparative evidence is limited.

AUTHORS' CONCLUSIONS

We found very low-certainty evidence that extended-release methylphenidate compared to placebo improved ADHD symptoms (small-to-moderate effects) measured on rating scales reported by participants, investigators, and peers such as family members. Methylphenidate had no effect on 'days missed at work' or serious adverse events, the effect on quality of life was small, and it increased the risk of several adverse effects. We rated the certainty of the evidence as 'very low' for all outcomes, due to high risk of bias, short trial durations, and limitations to the generalisability of the results. The benefits and harms of extended-release methylphenidate therefore remain uncertain.

Immediate-release methylphenidate for attention deficit hyperactivity disorder (ADHD) in adults

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is characterized by symptoms of inattention or impulsivity or both, and hyperactivity, which affect children, adolescents, and adults. In some countries, methylphenidate is the first option to treat adults with moderate or severe ADHD. However, evidence on the efficacy and adverse events of immediate-release (IR) methylphenidate in the treatment of ADHD in adults is limited and controversial.

OBJECTIVES

To evaluate the efficacy and harms (adverse events) of IR methylphenidate for treating ADHD in adults.

SEARCH METHODS

In January 2020, we searched CENTRAL, MEDLINE, Embase, eight additional databases and three trial registers. We also searched internal reports on the European Medicines Agency and the US Food and Drug Administration websites. We checked citations of included trials to identify additional trials not captured by the electronic searches.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing IR methylphenidate, at any dose, with placebo or other pharmacological interventions (including extended-release formulations of methylphenidate) for ADHD in adults. Primary outcomes comprised changes in the symptoms of ADHD (efficacy) and harms. Secondary outcomes included changes in the clinical impression of severity and improvement, level of functioning, depression, anxiety and quality of life. Outcomes could have been rated by investigators or participants.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data independently on the characteristics of the trials, participants, interventions; outcomes and financial conflict of interests. We resolved disagreements by discussion or consulting a third review author. We obtained additional, unpublished information from the authors of one included trial that had reported efficacy data in a graph. We calculated mean differences (MDs) or standardized MDs (SMDs) with 95% confidence intervals (CIs) for continuous data reported on the same or different scales, respectively. We summarized dichotomous variables as risk ratios (RRs) with 95% CI.

MAIN RESULTS

We included 10 trials published between 2001 and 2016 involving 497 adults with ADHD. Three trials were conducted in Europe and one in Argentina; the remaining trials did not report their location. The RCTs compared IR methylphenidate with placebo, an osmotic-release oral system (OROS) of methylphenidate (an extended-release formulation), an extended-release formulation of bupropion, lithium, and Pycnogenol® (maritime pine bark extract). Participants comprised outpatients, inpatients in addiction treatment, and adults willing to attend an intensive outpatient program for cocaine dependence. The duration of the follow-up ranged from 6 to 18 weeks. IR methylphenidate versus placebo We found very low-certainty evidence that, compared with placebo, IR methylphenidate may reduce symptoms of ADHD when measured with investigator-rated scales (MD -20.70, 95% CI -23.97 to -17.43; 1 trial, 146 participants; end scores; Adult ADHD Investigator Symptom Report Scale (AISRS), scored from 0 to 54), but the evidence is uncertain. The effect of IR methylphenidate on ADHD symptoms when measured with participant-rated scales was moderate, but the certainty of the evidence is very low (SMD -0.59, 95% CI -1.25 to 0.06; I² = 69%; 2 trials, 138 participants; end scores). There is very low-certainty evidence that, compared with placebo, IR methylphenidate may reduce the clinical impression of the severity of ADHD symptoms (MD -0.57, 95% CI -0.85 to -0.28; 2 trials, 139 participants; I² = 0%; change and end scores; Clinical Global Impression (CGI)-Severity scale (scored from 1 (very much improved) to 7 (very much worse))). There is low-certainty evidence that, compared with placebo, IR methylphenidate may slightly impact the clinical impression of an improvement in symptoms of ADHD (MD -0.94, 95% CI -1.37 to -0.51; 1 trial, 49 participants; end scores; CGI-Improvement scale (scored from 1 (very much improved) to 7 (very much worse))). There is no clear evidence of an effect on anxiety (MD -0.20, 95% CI -4.84 to 4.44; 1 trial, 19 participants; change scores; Hamilton Anxiety Scale (HAM-A; scored from 0 to 56); very low-certainty evidence) or depression (MD 2.80, 95% CI -0.09 to 5.69; 1 trial, 19 participants; change scores; Hamilton Depression Scale (HAM-D; scored from 0 to 52); very low-certainty evidence) in analyses comparing IR methylphenidate with placebo. IR methylphenidate versus lithium Compared with lithium, it is uncertain whether IR methylphenidate increases or decreases symptoms of ADHD (MD 0.60, 95% CI -3.11 to 4.31; 1 trial, 46 participants; end scores; Conners' Adult ADHD Rating Scale (scored from 0 to 198); very low-certainty evidence); anxiety (MD -0.80, 95% CI -4.49 to 2.89; 1 trial, 46 participants; end scores; HAM-A; very low-certainty evidence); or depression (MD -1.20, 95% CI -3.81 to 1.41, 1 trial, 46 participants; end scores; HAM-D scale; very low-certainty evidence). None of the included trials assessed participant-rated changes in symptoms of ADHD, or clinical impression of severity or improvement in participants treated with IR methylphenidate compared with lithium. Adverse events were poorly assessed and reported. We rated all trials at high risk of bias due to selective outcome reporting of harms and masking of outcome assessors (failure to blind outcome assessor to measure adverse events). Overall, four trials with 203 participants who received IR methylphenidate and 141 participants who received placebo described the occurrence of harms. The use of IR methylphenidate in these trials increased the risk of gastrointestinal complications (RR 1.96, 95% CI 1.13 to 2.95) and loss of appetite (RR 1.77, 95% CI 1.06 to 2.96). Cardiovascular adverse events were reported inconsistently, preventing a comprehensive analysis. One trial comparing IR methylphenidate to lithium reported five and nine adverse events, respectively. We considered four trials to have notable concerns of vested interests influencing the evidence, and authors from two trials omitted information related to the sources of funding and conflicts of interest.

AUTHORS' CONCLUSIONS

We found no certain evidence that IR methylphenidate compared with placebo or lithium can reduce symptoms of ADHD in adults (low- and very low-certainty evidence). Adults treated with IR methylphenidate are at increased risk of gastrointestinal and metabolic-related harms compared with placebo. Clinicians should consider whether it is appropriate to prescribe IR methylphenidate, given its limited efficacy and increased risk of harms. Future RCTs should explore the long-term efficacy and risks of IR methylphenidate, and the influence of conflicts of interest on reported effects.

Exocytosis-related genes and response to methylphenidate treatment in adults with ADHD

Experimental studies have demonstrated that methylphenidate (MPH) modulates the synaptic vesicle trafficking and synaptotagmin-1 (SytI) mRNA levels. SytI is a regulatory protein of the SNARE complex, a neurotransmitter exocytosis mediator. Despite this evidence, most SNARE complex-related genes have never been evaluated in attention-deficit/hyperactivity disorder (ADHD) pharmacogenetics. This study evaluates, for we believe the first time, polymorphisms on the SNARE complex-related genes STX1A (rs2228607), VAMP2 (26bp Ins/Del) and SYT1 (rs1880867 and rs2251214) on the response to immediate-release methylphenidate (IR-MPH) in a naturalistic sample of adults with ADHD. The sample comprised 433 subjects, of which 272 (62.8%) have completed the short-term IR-MPH treatment (at least 30 days). The main outcome measure was the categorical variable of short-term response to IR-MPH based on the Swanson, Nolan and Pelham Rating Scale version 4 (SNAP-IV), and on the clinical global impression-improvement scale. Additional analyses evaluated the percentage of SNAP-IV symptom reduction for each dimension as well as short- and long- (7 years) term treatment persistence. SYT1-rs2251214 was associated with the categorical short-term response to IR-MPH (P=0.006, P_FDR=0.028), and with the percentage of inattention and oppositional defiant disorder symptoms reduction (P=0.007, P_FDR=0.028 and P=0.017, P_FDR=0.048, respectively). SYT1-rs2251214 was also associated with short-term treatment persistence (P=0.018, P_FDR=0.048), and with months of treatment (P=0.002, P_FDR=0.016) in the long-term protocol. Our findings suggest that SYT1-rs2251214 presents a broad influence in IR-MPH response variability in adults with ADHD, being involved with both symptom response and treatment persistence. If such findings are replicated, SytI could represent a key element in MPH pharmacodynamics in adults with ADHD.

Clinical and neurobiological factors in the management of treatment refractory attention-deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent mental disorder of childhood, which often continues into adolescence and adulthood. Stimulants such as methylphenidate (MPH) and non-stimulants such as atomoxetine are effective medications for the treatment of ADHD. However, about 30% of patients do not respond to these medications. Pharmacological treatment for ADHD, although highly effective, is associated with marked variabilities in clinical response, optimal dosage needed and tolerability. This article provides an overview of up-to-date knowledge regarding the clinical and neurobiological factors which contribute to and help predict treatment-refractory ADHD. Pharmacogenetic, pharmacogenomics and neuroimaging studies are still controversial with respect to determining the associations between response to medication and genetic factors, thereby resulting in hypotheses that differences in the genetic factors and neuroimaging findings contribute to treatment outcome. Much research on the potential role of genotype in pharmacological effects has focused on the catecholaminergic gene related to executive functions. Many neuroimaging studies have also reported a relationship between treatment response and common patterns of brain structure or activity according to various genetic polymorphisms. When children, adolescents and adults with ADHD do not respond to MPH, we should consider additional pharmacological options, including other classes of psychostimulants, the nonstimulant atomoxetine, bupropion, tricyclic antidepressant, clonidine, guanfacine and lisdexamphetamine. Prudent choice of an appropriate medication and active engagement of children, parents, and teachers in daily management may help to ensure long-term adherence. Therefore, additional research might help to optimize the treatment of children, adolescents and adults with ADHD and to find new options for the treatment of patients who do not respond to stimulants and the other medications. Because these findings should be interpreted cautiously, further studies are needed to elucidate these issues more clearly.

Attention-deficit hyperactivity disorder in adults: A systematic review and meta-analysis of genetic, pharmacogenetic and biochemical studies

The adult form of attention-deficit/hyperactivity disorder has a prevalence of up to 5% and is the most severe long-term outcome of this common disorder. Family studies in clinical samples as well as twin studies suggest a familial liability and consequently different genes were investigated in association studies. Pharmacotherapy with methylphenidate (MPH) seems to be the first-line treatment of choice in adults with attention-deficit hyperactive disorder (ADHD) and some studies were conducted on the genes influencing the response to this drug. Finally some peripheral biomarkers were identified in ADHD adult patients. We believe this work is the first systematic review and meta-analysis of candidate gene association studies, pharmacogenetic and biochemical (metabolomics) studies performed in adults with ADHD to identify potential genetic, predictive and peripheral markers linked specifically to ADHD in adults. After screening 5129 records, we selected 87 studies of which 61 were available for candidate gene association studies, 5 for pharmacogenetics and 21 for biochemical studies. Of these, 15 genetic, 2 pharmacogenetic and 6 biochemical studies were included in the meta-analyses. We obtained an association between adult ADHD and the gene BAIAP2 (brain-specific angiogenesis inhibitor 1-associated protein 2), even after Bonferroni correction, with any heterogeneity in effect size and no publication bias. If we did not apply the Bonferroni correction, a trend was found for the carriers allele 9R of dopamine transporter SLC6A3 40 bp variable tandem repeat polymorphism (VNTR) and for 6/6 homozygotes of SLC6A3 30 bp VNTR. Negative results were obtained for the 9-6 haplotype, the dopamine receptor DRD4 48 bp VNTR, and the enzyme COMT SNP rs4680. Concerning pharmacogenetic studies, no association was found for the SLC6A3 40 bp and response to MPH with only two studies selected. For the metabolomics studies, no differences between ADHD adults and controls were found for salivary cortisol, whereas lower serum docosahexaenoic acid (DHA) levels were found in ADHD adults. This last association was significant even after Bonferroni correction and in absence of heterogeneity. Other polyunsaturated fatty acids (PUFAs) such as AA (arachidonic acid), EPA (eicosapentaenoic acid) and DyLA (dihomogammalinolenic acid) levels were not different between patients and controls. No publication biases were observed for these markers. Genes linked to dopaminergic, serotoninergic and noradrenergic signaling, metabolism (DBH, TPH1, TPH2, DDC, MAOA, MAOB, BCHE and TH), neurodevelopment (BDNF and others), the SNARE system and other forty genes/proteins related to different pathways were not meta-analyzed due to insufficient data. In conclusion, we found that there were not enough genetic, pharmacogenetic and biochemical studies of ADHD in adults and that more investigations are needed. Moreover we confirmed a significant role of BAIAP2 and DHA in the etiology of ADHD exclusively in adults. Future research should be focused on the replication of these findings and to assess their specificity for ADHD.

Should we keep on? Looking into pharmacogenomics of ADHD in adulthood from a different perspective

A considerable proportion of adults with attention-deficit/hyperactivity disorder (ADHD) do not respond to the treatment with methylphenidate. This scenario could be due to inherited interindividual differences that may alter pharmacologic treatment response. In this sense, in 2012 we conducted a systematic search on PUBMED-indexed literature for articles containing information about pharmacogenomics of ADHD in adults. Five studies were found on methylphenidate pharmacogenomics and the only significant association was reported by one particular study. However, this single association with the SLC6A3 gene was not replicated in two subsequent reports. In the present review, although we could not find additional pharmacogenomics studies, we discuss these up-to-date findings and suggest new approaches for this field. Additionally, using systeomic-oriented databases, we provide a broad picture of new possible candidate genes as well as potential gene-gene interactions to be investigated in pharmacogenomics of persistent ADHD.

Toward quality care in ADHD: defining the goals of treatment

OBJECTIVE

Therapeutic goals for chronic mental disorders like major depressive disorder (MDD) and schizophrenia have evolved in parallel with the growing medical knowledge about the course and treatment of these disorders. Although the knowledge base regarding the clinical course of ADHD, a chronic psychiatric disorder, has evolved beyond symptomatic improvement and short-term treatment response, long-term goals, such as functional remission, have not yet been clearly defined.

METHOD

A PubMed literature search was conducted to investigate the therapeutic goals of pharmacologic treatment referenced in the published literature from January 1998 through February 2010 using the following commonly used ADHD treatments as keywords: amphetamine, methylphenidate, atomoxetine, lisdexamfetamine, guanfacine, and clonidine. This search was then combined with an additional search that included the following outcome keywords: remission, relapse, remit, response, normal, normalization, recovery, and effectiveness.

RESULTS

Our search identified 102 publications. The majority (88.2% [90/102]) of these contained predefined criteria for treatment response. Predefined criteria for normalization and remission and/or relapse were presented in 4.9% (5/102), 12.7% (13/102), and 3.9% (4/102) of publications, respectively. There was a lack of consistency between the instruments used to measure outcomes as well as the criteria used to define treatment response, normalization, and remission as well as relapse.

CONCLUSION

The therapeutic goals in treating ADHD should address optimal treatment outcomes that go beyond modest reductions of ADHD symptoms to include syndromatic, symptomatic, and functional remission. Future work should focus on reliable and valid tools to measure these outcomes in the clinical trial setting.

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.

ADHD pharmacogenetics across the life cycle: New findings and perspectives

Attention-deficit/hyperactivity disorder (ADHD) is a complex and heterogeneous disorder, affecting individuals across the life cycle. Although its etiology is not yet completely understood, genetics plays a substantial role. Pharmacological treatment is considered effective and safe for children and adults, but there is considerable inter-individual variability among patients regarding response to medication, required doses, and adverse events. We present here a systematic review of the literature on ADHD pharmacogenetics to provide a critical discussion of the existent findings, new approaches, limitations, and recommendations for future research. Our main findings are: first, the number of studies continues to grow, making ADHD one of the mental health areas with more pharmacogenetic studies. Second, there has been a focus shift on ADHD pharmacogenetic studies in the last years. There is an increasing number of studies assessing gene-gene and gene-environment interactions, using genome-wide association approaches, neuroimaging, and assessing pharmacokinetic properties. Third and most importantly, the heterogeneity in methodological strategies employed by different studies remains impressive. The question whether pharmacogenetics studies of ADHD will improve clinical management by shifting from trial-and-error approach to a pharmacological regimen that takes into account the individual variability remains unanswered. © 2014 Wiley Periodicals, Inc.

Pharmacogenetics of response to methylphenidate in adult patients with Attention-Deficit/Hyperactivity Disorder (ADHD): a systematic review

Methylphenidate (MPH) is a first line option in the psychopharmacologic treatment of adults with Attention-Deficit/Hyperactivity Disorder (ADHD). However, there is a considerable proportion of adult patients who do not respond to treatment with MPH or discontinue drug therapy. Since effects of genetic variants in the response to MPH treatment might explain these negative outcomes, we conducted an electronic systematic search of MEDLINE-indexed literature looking for articles containing information about pharmacogenetics of ADHD in adults published until January, 2012. The keywords used were 'ADHD', 'Attention-Deficit/Hyperactivity Disorder' and 'gene' in combination with methylphenidate, amphetamine or atomoxetine. Only 5 pharmacogenetic studies on adult ADHD met inclusion criteria. The results evidenced that most findings obtained so far are negative, and all studies focused on MPH response. There is only one positive result, for a polymorphism at the dopamine transporter gene (DAT1) gene. The current state of the art in adult ADHD implies that pharmacogenetic tests are far from routine clinical practice. However, the integration of these studies with neuroimaging and neuropsychological tests may help to understand mechanisms of drug action and the pathophysiology of ADHD.

Meta-analysis of the association between dopamine transporter genotype and response to methylphenidate treatment in ADHD

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent childhood-onset neuropsychiatric disorder. Treatment with methylphenidate, which blocks dopamine and noradrenaline transporters, is clinically efficacious in reducing the symptoms of ADHD. However, a considerable proportion of patients show no or only insufficient response to methylphenidate. Following a pharmacogenetic approach, a number of studies have suggested that heterogeneity in treatment response across subjects might to some extent be due to genetic factors. In particular, a variable number tandem repeat (VNTR) polymorphism in the 3' untranslated region of the SLC6A3 gene, which codes for the dopamine transporter, has been considered as a predictor of treatment success. However, the literature has so far been inconsistent. Here we present results of a meta-analysis of studies investigating the moderating effect of the SLC6A3 VNTR on response to methylphenidate treatment in subjects with ADHD. Outcome measures from 16 studies including data from 1572 subjects were entered into a random-effects model. There was no significant summary effect for the SLC6A3 VNTR on the response to methylphenidate treatment (P>0.5) and no effect on specific symptom dimensions of hyperactivity/impulsivity and inattention (all P>0.2). However, in a subanalysis of naturalistic trials, we observed a significant effect of d=-0.36 (P=0.03), indicating that 10R homozygotes show less improvement in symptoms following treatment than the non-10/10 carriers. This meta-analysis indicates that SLC6A3 VNTR is not a reliable predictor of methylphenidate treatment success in ADHD. Our study leaves unanswered the question of whether other genetic polymorphisms or nongenetic factors may contribute to the observed heterogeneity in treatment response across ADHD subjects.

No significant association between genetic variants in 7 candidate genes and response to methylphenidate treatment in adult patients with ADHD

Results from pharmacogenetic investigations of methylphenidate (MPH) response in patients with ADHD are still inconsistent, especially among adults. This study investigates the role of genetic variants (SLC6A4, HTR1B, TPH2, DBH, DRD4, COMT, and SNAP25) in the response to MPH in a sample of 164 adults. Genes were chosen owing to previous evidence for an influence in ADHD susceptibility. No significant differences in allele or genotype frequencies between MPH responders and nonresponders were detected. In conclusion, our findings do not support an effect of these genes in the pharmacogenetics of MPH among adults with ADHD.

Psychiatric pharmacogenomics in pediatric psychopharmacology

This article provides an overview of where psychiatric pharmacogenomic testing stands as an emerging clinical tool in modern psychotropic prescribing practice, specifically in the pediatric population. This practical discussion is organized around the state of psychiatric pharmacogenomics research when choosing psychopharmacologic interventions in the most commonly encountered mental illnesses in youth. As with the rest of the topics on psychopharmacology for children and adolescents in this publication, a clinical vignette is presented, this one highlighting a clinical case of a 16 year old genotyped during hospitalization for recalcitrant depression.

Dopaminergic and noradrenergic gene polymorphisms and response to methylphenidate in korean children with attention-deficit/hyperactivity disorder: is there an interaction?

OBJECTIVE

We aimed to investigate the independent and interaction effects of dopamine transporter gene (DAT1), dopamine D4 receptor gene (DRD4), alpha-2A adrenergic receptor gene (ADRA2A), and norepinephrine transporter gene (NET1), with regard to treatment response to methylphenidate (MPH) in attention-deficit/hyperactivity disorder (ADHD).

METHODS

The participants of the study were 103 children and adolescents (ages 9.1±2.1 years) diagnosed as having ADHD according to American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV) criteria. They were enrolled in an 8-week, open-label trial of MPH. The good responder group was defined as subjects having an ≥50% decrease in the ADHD Rating Scale-IV (ADHD-RS) total score from the baseline, and at the same time a Clinical Global Impressions-Improvement Scale (CGI-I) score of 1 or 2, both at the 8th week of MPH treatment. Multivariate stepwise logistic regression was performed to examine the independent and interaction effects of genotypes on the dichotomized MPH treatment response.

RESULTS

Significant interaction effects on MPH response were detected between the genotypes of the DRD4 variable number of tandem repeat (VNTR) polymorphisms and those of either the ADRA2A DraI or the NET1 -3081(A/T) polymorphisms; significant interaction effects were also detected between the genotypes of the ADRA2A DraI polymorphisms and those of either the NET1 G1287A or the NET1 -3081(A/T) polymorphisms (Nagelkerke R(2)=0.40). No significant independent effect of a genotype was detected according to the stepwise logistic regression results.

CONCLUSION

The results suggest that genes involved in the dopaminergic and noradrenergic systems might interact to form important predictors of short-term response to MPH.

The genetics of attention deficit/hyperactivity disorder in adults, a review

The adult form of attention deficit/hyperactivity disorder (aADHD) has a prevalence of up to 5% and is the most severe long-term outcome of this common neurodevelopmental disorder. Family studies in clinical samples suggest an increased familial liability for aADHD compared with childhood ADHD (cADHD), whereas twin studies based on self-rated symptoms in adult population samples show moderate heritability estimates of 30-40%. However, using multiple sources of information, the heritability of clinically diagnosed aADHD and cADHD is very similar. Results of candidate gene as well as genome-wide molecular genetic studies in aADHD samples implicate some of the same genes involved in ADHD in children, although in some cases different alleles and different genes may be responsible for adult versus childhood ADHD. Linkage studies have been successful in identifying loci for aADHD and led to the identification of LPHN3 and CDH13 as novel genes associated with ADHD across the lifespan. In addition, studies of rare genetic variants have identified probable causative mutations for aADHD. Use of endophenotypes based on neuropsychology and neuroimaging, as well as next-generation genome analysis and improved statistical and bioinformatic analysis methods hold the promise of identifying additional genetic variants involved in disease etiology. Large, international collaborations have paved the way for well-powered studies. Progress in identifying aADHD risk genes may provide us with tools for the prediction of disease progression in the clinic and better treatment, and ultimately may help to prevent persistence of ADHD into adulthood.

Relationship of DAT1 and adult ADHD to task-positive and task-negative working memory networks

Alterations in working memory, default-mode network (DMN), and dopamine transporter have all been proposed as endophenotypes for attention-deficit/hyperactivity disorder (ADHD). Despite evidence that these systems are interrelated, their relationship to each other has never been studied in the context of ADHD. In order to understand the potential mediating effects of task-positive and task-negative networks between DAT1 and diagnosis, we tested effects of genotype and diagnosis on regions of positive and negative BOLD signal change (as measured with fMRI) in 53 adults with ADHD and 38 control subjects during a working memory task. We also examined the relationship of these responses to ADHD symptoms. Our results yielded four principal findings: 1) association of the DAT1 9R allele with adult ADHD, 2) marginal DAT1 association with task-related suppression in left medial PFC, 3) marginal genotype×diagnosis interaction in the dorsal anterior cingulate cortex, and 4) correlation of DMN suppression to ADHD symptoms. These findings replicate the association of the 9R allele with adult ADHD. Further, we show that DMN suppression is likely linked to DAT1 and to severity of inattention in ADHD. DMN may therefore be a target of DAT1 effects, and lie on the path between the gene and inattention in ADHD.

Genome-wide association study of blood pressure response to methylphenidate treatment of attention-deficit/hyperactivity disorder

OBJECTIVE

We conducted a genome-wide association study of blood pressure in an open-label study of the methylphenidate transdermal system (MTS) for the treatment of attention-deficit/hyperactivity disorder (ADHD).

METHOD

Genotyping was conducted with the Affymetrix Genome-Wide Human SNP Array 6.0. Multivariate association analyses were conducted using the software package PLINK. After data cleaning and quality control we tested 316,934 SNPs in 140 children with ADHD.

RESULTS

We observed no genome-wide statistically significant findings, but a SNP in a K(+)-dependent Na(+)/Ca(2+) exchanger expressed in vascular smooth muscle (SLC24A3) was included in our top associations at p<1E-04. Genetic enrichment analyses of genes with ≥1 SNP significant at p<0.01, implicated several functional categories (FERM domain, p=5.0E-07; immunoglobulin domain, p=8.1E-06; the transmembrane region, p=4.4E-05; channel activity, p=2.0E-04; and type-III fibronectins, p=2.7E-05) harboring genes previously associated with related cardiovascular phenotypes.

CONCLUSIONS

The hypothesis generating results from this study suggests that polymorphisms in several genes consistently associated with cardiovascular diseases may impact changes in blood pressure observed with methylphenidate pharmacotherapy in children with ADHD.

Cognitive enhancement by drugs in health and disease

Attempts to improve cognitive function in patients with brain disorders have become the focus of intensive research efforts. A recent emerging trend is the use of so-called cognitive enhancers by healthy individuals. Here, we consider some of the effects - positive and negative - that current drugs have in neurological conditions and healthy people. We conclude that, to date, experimental and clinical studies have demonstrated relatively modest overall effects, most probably because of substantial variability in response both across and within individuals. We discuss biological factors that might account for such variability and highlight the need to improve testing methods and to extend our understanding of how drugs modulate specific cognitive processes at the systems or network level.

A current update on ADHD pharmacogenomics

Pharmacological treatment for attention deficit hyperactivity disorder, although highly effective, presents a marked variability in clinical response, optimal dosage needed and tolerability. Clinical and neurobiological investigations have juxtaposed findings on both response to medication and etiologic factors, generating the hypothesis that genetic factors may underlie differences in treatment outcome. Over the last decade, research has focused on the catecholaminergic system to investigate a potential role of genotype on pharmacological effect. Despite an increasing number of associations reported (for methylphenidate, nine in 2005, 24 in 2008 and 52 reported in the current article), the identification of clinically relevant genetic predictors of treatment response remains a challenge. At present, additional studies are required to allow for a shift from a trial-and-error approach to a more rational pharmacologic regimen that takes into account the likelihood of treatment effectiveness at the individual level.

Progress and promise of attention-deficit hyperactivity disorder pharmacogenetics

One strategy for understanding variability in attention-deficit hyperactivity disorder (ADHD) medication response, and therefore redressing the current trial-and-error approach to ADHD medication management, is to identify genetic moderators of treatment. This article summarizes ADHD pharmacogenetic investigative efforts to date, which have primarily focused on short-term response to methylphenidate and largely been limited by modest sample sizes. The most well studied genes include the dopamine transporter and dopamine D(4) receptor, with additional genes that have been significantly associated with stimulant medication response including the adrenergic alpha(2A)-receptor, catechol-O-methyltransferase, D(5) receptor, noradrenaline (norepinephrine) transporter protein 1 and synaptosomal-associated protein 25 kDa. Unfortunately, results of current ADHD pharmacogenetic studies have not been entirely consistent, possibly due to differences in study design, medication dosing regimens and outcome measures. Future directions for ADHD pharmacogenetics investigations may include examination of drug-metabolizing enzymes and a wider range of stimulant and non-stimulant medications. In addition, researchers are increasingly interested in going beyond the individual candidate gene approach to investigate gene-gene interactions or pathways, effect modification by additional environmental exposures and whole genome approaches. Advancements in ADHD pharmacogenetics will be facilitated by multi-site collaborations to obtain larger sample sizes using standardized protocols. Although ADHD pharmacogenetic efforts are still in a relatively early stage, their potential clinical applications may include the development of treatment efficacy and adverse effect prediction algorithms that incorporate the interplay of genetic and environmental factors, as well as the development of novel ADHD treatments.

Response to methylphenidate is not influenced by DAT1 polymorphisms in a sample of Brazilian adult patients with ADHD

Several lines of evidence suggest a relevant role for the dopamine transporter (DAT1) gene not only as a susceptibility factor for attention-deficit hyperactivity disorder (ADHD), but also as a predictor of individual methylphenidate (MPH) response. Pharmacogenetic studies of MPH response in ADHD have mainly focused on the 40-bp variable number of tandem repeats (VNTR) in the 3' untranslated region (3'-UTR) of DAT1. Most studies were performed in samples of children and conflicting findings were obtained. Only two studies have assessed 3'-VNTR in samples of adults-one with positive and the other with negative findings. In the present study, we investigate three potentially relevant polymorphisms in DAT1 gene (-839 C > T; Int8 VNTR and 3'-VNTR), and their possible role in therapeutic response to MPH treatment in a sample of 171 Brazilian adults with ADHD. The diagnostic procedures followed the DSM-IV criteria and the outcome measures were the scales Swanson, Nolan, and Pelham Rating scale version IV and the Clinical Global Impression-Severity Scale, applied at the beginning and after the 30th day of treatment. Drug response was assessed by both categorical and dimensional approaches. There was no effect of any DAT1 polymorphisms or haplotypes on MPH response. This is the second report demonstrating absence of differences in MPH response according to DAT1 genotypes in adults with ADHD. Although DAT protein is crucial for the effect of MPH, genetic variations in DAT1 gene probably do not have a significant clinical role in this sample of adults with ADHD.

A candidate gene analysis of methylphenidate response in attention-deficit/hyperactivity disorder

OBJECTIVE

This study examines the potential role of candidate genes in moderating treatment effects of methylphenidate (MPH) in attention-deficit/hyperactivity disorder (ADHD).

METHOD

Eighty-two subjects with ADHD aged 6 to 17 years participated in a prospective, double-blind, placebo-controlled, multiple-dose, crossover titration trial of immediate release MPH three times daily. The subjects were assessed on a variety of parent and clinician ratings and a laboratory math test. Data reduction based on principal components analysis identified statistically derived efficacy and side effect outcomes.

RESULTS

Attention-deficit/hyperactivity disorder symptom response was predicted by polymorphisms at the serotonin transporter (SLC6A4) intron 2 VNTR (p = .01), with a suggested trend for catechol-O-methyltransferase (COMT) (p = .04). Gene × dose interactions were noted on math test outcomes for the dopamine D4 receptor (DRD4) promoter (p = .008), DRD4 exon 3 VNTR (p = .006), and SLC6A4 promoter insertion/deletion polymorphism (5HTTLPR) (p = .02). Irritability was predicted by COMT (p = .02). Vegetative symptoms were predicted by 5HTTLPR (p = .003). No significant effects were noted for the dopamine transporter (SLC6A3) or synaptosomal-associated protein 25 (SNAP25).

CONCLUSIONS

This article confirms and expands previous studies suggesting that genes moderate ADHD treatment response. The ADHD outcomes are not unitary but reflect both behavioral and learning domains that are likely influenced by different genes. Future research should emphasize candidate gene and genome-wide association studies in larger samples, symptom reduction as well as side effects outcomes, and responses over full therapeutic dose ranges to assess differences in both gene and gene × dose interactive effects.

Pharmacogenetic treatments for drug addiction: cocaine, amphetamine and methamphetamine

BACKGROUND

Pharmacogenetics uses genetic variation to predict individual differences in response to medications and holds much promise to improve treatment of addictive disorders.

OBJECTIVES

To review how genetic variation affects responses to cocaine, amphetamine, and methamphetamine and how this information may guide pharmacotherapy.

METHODS

We performed a cross-referenced literature search on pharmacogenetics, cocaine, amphetamine, and methamphetamine.

RESULTS

We describe functional genetic variants for enzymes dopamine-beta-hydroxylase (DbetaH), catechol-O-methyltransferase (COMT), and dopamine transporter (DAT1), dopamine D4 receptor, and brain-derived neurotrophic factor (BDNF). A single nucleotide polymorphism (SNP; C-1021T) in the DbetaH gene is relevant to paranoia associated with disulfiram pharmacotherapy for cocaine addiction. Individuals with variable number tandem repeats (VNTR) of the SLC6A3 gene 3'-untranslated region polymorphism of DAT1 have altered responses to drugs. The 10/10 repeat respond poorly to methylphenidate pharmacotherapy and the 9/9 DAT1 variant show blunted euphoria and physiological response to amphetamine. COMT, D4 receptor, and BDNF polymorphisms are linked to methamphetamine abuse and psychosis.

CONCLUSIONS

Disulfiram and methylphenidate pharmacotherapies for cocaine addiction are optimized by considering polymorphisms affecting DbetaH and DAT1 respectively. Altered subjective effects for amphetamine in DAT1 VNTR variants suggest a 'protected' phenotype.

SCIENTIFIC SIGNIFICANCE

Pharmacogenetic-based treatments for psychostimulant addiction are critical for successful treatment.

Dopamine-related genotypes and the dose-response effect of methylphenidate on eating in attention-deficit/hyperactivity disorder youths

OBJECTIVE

There are individual differences in the effects of methylphenidate (MPH), a dopamine (DA) transport inhibitor, on appetite in children with attention-deficit/hyperactivity disorder (ADHD). One potential moderating factor is variation in brain DA activity, which is influenced by dopamine-related genes: the DA transporter (DAT) (SLC6A3), the DA D2 receptor (DRD2), and the DA D4 receptor (DRD4) genes. The purpose of this study was to explore the relationship between dopamine-related gene polymorphisms and food consumption in ADHD children receiving varying doses of MPH.

METHODS

In a randomized, within-subject, double-blind design, 58 ADHD children (ages 6-12 years) received placebo, 0.15, 0.3, or 0.6 mg/kg of MPH three times daily over 9 weeks. Observations of percent lunch consumed as a function of dopamine-related genotypes and MPH dose were analyzed using mixed effects regression models.

RESULTS

A significant dose-response reduction in eating was observed across all genotypes (p < 0.001). There was an interaction of DAT SLC6A3 and DRD2 genotypes and dose, because 9/9 DAT children showed a stronger effect of dose when compared with the 9/10 and 10/10 children (p < 0.001) and DRD2 A2/A2 children showed a stronger effect of dose when compared with A1/A1 and A1/A2 children combined (p = 0.007). There was no significant interaction of dose by DRD4 genotype.

CONCLUSIONS

Lunch consumption decreased as a function of MPH dose. DA-related genotypes associated with greater brain DA signaling moderated the influence of drug on consumption. These results provide information relevant to predicting which children are likely to experience the greatest appetite suppression when taking MPH.

Pharmacogenetics of methylphenidate response in attention deficit/hyperactivity disorder: association with the dopamine transporter gene (SLC6A3)

Pharmacogenetic studies investigating the 40-bp VNTR polymorphism at SLC6A3 and methylphenidate response have shown conflicting results and large differences in study design and efficacy endpoints. Our objective was to investigate the relation between the 3'-VNTR at SLC6A3 and variability in methylphenidate response in a sample of 141 ADHD children and adolescents, assessed before and after methylphenidate treatment with both clinical and neuropsychological outcome measures. 10-R homozygotes were significantly overrepresented in the low response group, but no genotype effect was shown in cognitive variables improvement. A meta-analysis of pharmacogenetic studies with comparable data (responders vs. non-responders) on a total of 475 subjects showed a significant association between the 10-10 genotype and low rates of methylphenidate response (mean Odds Ratio = 0.46; 95% CI [0.28-0.76]). Heterogeneity between these studies did not reach a significant level but, as publications with different endpoints were excluded from this meta-analysis, our results do not rule out a possible influence of study design.

Genome-wide association study of response to methylphenidate in 187 children with attention-deficit/hyperactivity disorder

We conducted a genome-wide association study of symptom response in an open-label study of a methylphenidate transdermal system (MTS). All DNA extraction and genotyping was conducted at SUNY Upstate Medical University using the Affymetrix Genome-Wide Human SNP Array 6.0. All quality control and association analyses were conducted using the software package PLINK. After data cleaning and quality control, there were 187 subjects (72% (N = 135) male) with mean age 9.2 +/- 2.0 years and 319,722 SNPs available for analysis. The most statistically significant association (rs9627183 and rs11134178; P = 3 x 10(-6)) fell short of the threshold for a genome-wide significant association. The most intriguing association among suggestive findings (rs3792452; P = 2.6 x 10(-5)) was with the metabotropic glutamate receptor 7 gene (GRM7) as it is expressed in brain structures also previously associated with ADHD. Among the 102 available SNPs covering previously studied candidate genes, two SNPs within the norepinephrine transporter gene (NET, SLC6A2) were significant at P < or = 1 x 10(-2). These results should be considered preliminary until replicated in larger adequately powered, controlled samples but do suggest that noradrenergic and possibly glutaminergic genes may be involved with response to methylphenidate.

Catechol-O-methyltransferase Val158Met polymorphism is associated with methylphenidate response in ADHD children

Methylphenidate is the most frequently prescribed drug in the treatment of attention deficit hyperactivity disorder (ADHD) but it is not effective in every case. Therefore, identifying genetic and/or biological markers predicting drug-response is increasingly important. Here we present a case-control study and pharmacogenetic association analyses in ADHD investigating three dopaminergic polymorphisms. Previous studies suggested variable number of tandem repeats (VNTR) in the dopamine D4 receptor (DRD4) and the dopamine transporter (DAT1) genes as genetic risk factors for ADHD and as possible markers of methylphenidate response. Our results did not indicate substantial involvement of these two VNTRs in ADHD, however, both the case-control and the pharmacogenetic analyses showed significant role of the high activity Val-allele of cathecol-O-methyltransferase (COMT) Val158Met polymorphism in our ADHD population. The Val-allele was more frequent in the ADHD group (n = 173) compared to the healthy population (P = 0.016). The categorical analysis of 90 responders versus 32 non-responders showed an association between the Val-allele or Val/Val genotype and good methylphenidate response (P = 0.009 and P = 0.034, respectively). Analyzing symptom severity as a continuous trait, significant interaction of COMT genotype and methylphenidate was found on the Hyperactivity-Impulsivity scale (P = 0.044). Symptom severity scores of all three genotype groups decreased following methylphenidate administration (P < 0.001), however Val/Val homozygote children had significantly less severe symptoms than those with Met/Met genotype after treatment (P = 0.015). This interaction might reflect the regulatory effect of COMT dominated prefrontal dopamine transmission on subcortical dopamine systems, which are the actual site of methylphenidate action.

The impact of individual and methodological factors in the variability of response to methylphenidate in ADHD pharmacogenetic studies from four different continents

Several studies have evaluated the association between individual polymorphisms and response to methylphenidate (MPH) in subjects with attention-deficit/hyperactivity disorder (ADHD). There are few replication studies for each polymorphism of interest and results are sometimes inconsistent in this field. Although data collection from multiple international sites would allow large sample sizes, this approach has been criticized for introducing sampling variability due to differences in ethnicity and methodology between studies. To examine these issues, we aggregated nine pharmacogenetic studies from four different continents and conducted a two stage analysis: (a) we evaluated the role of methodological aspects in the variability of ADHD symptom improvement between studies using meta-regression analysis; (b) we assessed the role of individual characteristics of the subjects in the variability of ADHD symptoms improvement using multivariate regression analysis in the same data sets. At the study level, from five evaluated factors, only the design of the study (open studies vs. randomized controlled trials) was significantly associated with heterogeneity of results (P = 0.001). At the individual level, age (P < 0.001), comorbid oppositional defiant disorder (P < 0.001), and pre-treatment scores (P < 0.001) were associated with change of ADHD scores with treatment in the final multivariate model. Our results suggest that joint analyses of pharmacogenetic studies are feasible and promising, since fixed variables, such as the site where the study was conducted, were not related to results. Nevertheless, stratified analyses according to the design of the study must be preferentially conducted and the role of individual factors such as demographic data and comorbid profile as confounders should be assessed.

Spatial attentional bias as a marker of genetic risk, symptom severity, and stimulant response in ADHD

Attention-deficit hyperactivity disorder (ADHD) is a heritable childhood onset disorder that is marked by variability at multiple levels including clinical presentation, cognitive profile, and response to stimulant medications. It has been suggested that this variability may reflect etiological differences, particularly, at the level of underlying genetics. This study examined whether an attentional phenotype-spatial attentional bias could serve as a marker of symptom severity, genetic risk, and stimulant response in ADHD. A total of 96 children and adolescents with ADHD were assessed on the Landmark Task, which is a sensitive measure of spatial attentional bias. All children were genotyped for polymorphisms (3' untranslated (UTR) and intron 8 variable number of tandem repeats (VNTRs)) of the dopamine transporter gene (DAT1). Spatial attentional bias correlated with ADHD symptom levels and varied according to DAT1 genotype. Children who were homozygous for the 10-repeat allele of the DAT1 3'-UTR VNTR displayed a rightward attentional bias and had higher symptom levels compared to those with the low-risk genotype. A total of 26 of these children who were medication naive performed the Landmark Task at baseline and then again after 6 weeks of stimulant medication. Left-sided inattention (rightward bias) at baseline was associated with an enhanced response to stimulants at 6 weeks. Moreover, changes in spatial bias with stimulant medications, varied as a function of DAT1 genotype. This study suggests an attentional phenotype that relates to symptom severity and genetic risk for ADHD, and may have utility in predicting stimulant response in ADHD.

The Pharmacogenomic Era: Promise for Personalizing ADHD Therapy

Attention deficit hyperactivity disorder (ADHD) treatment is often determined empirically through trial and error until an adequate response is obtained or side effects occur. ADHD is highly heritable and individuals experience wide individual variability in response to ADHD medications, suggesting that the mechanism of action of stimulant medications may provide clues for genetic predictors of response. The promise of ADHD pharmacogenetics is far-reaching and includes the potential to develop individualized medication regimens that improve symptom response, decrease risk for side effects, improve long-term tolerability, and thus contribute to long-term treatment compliance and improved effectiveness. Early ADHD pharmacogenetic studies have focused predominantly on catecholamine pathway genes and response to methylphenidate. Future efforts will also examine a wider range of stimulant and nonstimulant medications on a range of outcome measures and durations. Based on these studies, the potential for personalizing ADHD treatment in clinical practice will be determined.

Response to methylphenidate in adults with ADHD is associated with a polymorphism in SLC6A3 (DAT1)

In this pharmacogenetic study in adults with ADHD (n = 42), a stratified analysis was performed of the association between response to methylphenidate (MPH), assessed under double-blind conditions, and polymorphisms in the genes encoding the dopamine transporter, SLC6A3 (DAT1), the norepinephrine transporter, SLC6A2 (NET), and the dopamine receptor D4, DRD4. The VNTR polymorphism in the 3' untranslated region of SLC6A3 was significantly associated with an increased likelihood of a response to MPH treatment (OR 3.8; 95% CI 1.0-15.2, and OR 5.4; 95% CI 1.4-21.9, depending on the definition of response) in carriers of a single 10-repeat allele compared to patients with the 10/10 genotype. The polymorphisms in DRD4 and the SLC6A2 were not associated with treatment response. This study supports a role of the SLC6A3 genotype in determining the response to MPH in the treatment of adults with ADHD.

Behavioral genetic contributions to the study of addiction-related amphetamine effects

Amphetamines, including methamphetamine, pose a significant cost to society due to significant numbers of amphetamine-abusing individuals who suffer major health-related consequences. In addition, methamphetamine use is associated with heightened rates of violent and property-related crimes. The current paper reviews the existing literature addressing genetic differences in mice that impact behavioral responses thought to be relevant to the abuse of amphetamine and amphetamine-like drugs. Summarized are studies that used inbred strains, selected lines, single-gene knockouts and transgenics, and quantitative trait locus (QTL) mapping populations. Acute sensitivity, neuroadaptive responses, rewarding and conditioned effects are among those reviewed. Some gene mapping work has been accomplished, and although no amphetamine-related complex trait genes have been definitively identified, translational work leading from results in the mouse to studies performed in humans is beginning to emerge. The majority of genetic investigations have utilized single-gene knockout mice and have concentrated on dopamine- and glutamate-related genes. Genes that code for cell support and signaling molecules are also well-represented. There is a large behavioral genetic literature on responsiveness to amphetamines, but a considerably smaller literature focused on genes that influence the development and acceleration of amphetamine use, withdrawal, relapse, and behavioral toxicity. Also missing are genetic investigations into the effects of amphetamines on social behaviors. This information might help to identify at-risk individuals and in the future to develop treatments that take advantage of individualized genetic information.

ADHD genetics: 2007 update

Attention-deficit/hyperactivity disorder (ADHD) is highly heritable. Confirmed association has been reported for several candidate genes, including DAT1, DRD4, SNAP-25, DRD5, 5HTT, HTR1B, and DBH; however, these confer relatively small risk. Family-based linkage studies have identified a number of chromosomal regions containing potential ADHD predisposing loci, some overlapping in two or more studies, including 5p, 6q, 7p, 11q, 12q, and 17p. New large-scale studies that apply recent technological advances to perform high-density genotyping of the entire genome, in combination with information on the haplotype structure of the human genome, now allow testing of single-nucleotide polymorphism association with disease phenotype without any a priori hypothesis. They may contribute further to our understanding of the genetic factors involved in ADHD. The heterogeneous complex ADHD phenotype, as well as epigenetic factors may be contributing to the challenge of genetic studies. Samples that include limited age ranges may have better success at uncovering genes whose expression is limited to specific developmental stages.