Pharmacogenetic predictors of methylphenidate dose-response in attention-deficit/hyperactivity disorder

Catechol-O-methyltransferase Val158-Met polymorphism and a response of hyperactive-impulsive symptoms to methylphenidate: A replication study from South Korea

We investigated the association between the catechol-O-methyltransferase (COMT) Val(158)-Met (rs4680) genotype and both subjective and objective treatment responses to methylphenidate in Korean children with attention-deficit/hyperactivity disorder (ADHD). We enrolled 120 medication-naïve children with ADHD in an open-label, 8-week trial of methylphenidate. The participants were genotyped and evaluated using the Clinical Global Impression Scale and the ADHD Rating Scale-IV (ADHD-RS), and completed the Continuous Performance Test (CPT) before and after treatment. We found a significant association between the COMT Val/Val genotype and a good response, in terms of hyperactive-impulsive scores on the ADHD-RS (odds ratio (OR) = 2.61; p = 0.044) and response-time variability on the CPT (OR = 2.66; p = 0.028). The association of the COMT Val/Val genotype with a good response, in terms of response time variability, was significant in both the sub-sample of combined-type (OR = 3.45; p = 0.026) and sub-sample of inattentive-type (OR = 5.52; p = 0.029); but the association with a good response in terms of hyperactive-impulsive scores was not significant in sub-sample analyses. Although the reported nominally significant associations did not stay significant after correcting for multiple testing, our results support previous findings about the possible involvement of the COMT (Val(158)-Met) polymorphism in the treatment response to methylphenidate in children with ADHD.

Dopamine transporter genotype and stimulant dose-response in youth with attention-deficit/hyperactivity disorder

OBJECTIVES

This study seeks to determine if variation in the dopamine transporter gene (SLC6A3/DAT1) moderates the dose-response effects of long-acting dexmethylphenidate (D-MPH) and mixed amphetamine salts (MAS) in children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

Fifty-six children and adolescents (mean age=11.7±2.2) participated in a double-blind, two period crossover, dose-response study with a randomized placebo week in each 4 week drug period. Each period consisted of sequential week-long exposures to three dose levels (10, 20, 25-30 mg, depending upon weight) of D-MPH or MAS.

RESULTS

Doses of 10-20 mg of either D-MPH or MAS had little to no effect on hyperactivity-impulsivity and total ADHD symptom scores in subjects with the 9/9 genotype; this was in contrast to the dose-response curves of subjects with either the 10/10 or 10/9 genotype.

CONCLUSIONS

ADHD youth with the 9/9 genotype may require higher stimulant doses to achieve adequate symptom control.

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.

Positive effects of methylphenidate on hyperactivity are moderated by monoaminergic gene variants in children with autism spectrum disorders

Methylphenidate (MPH) reduces hyperactive-impulsive symptoms common in children with autism spectrum disorders (ASDs), however, response and tolerability varies widely. We hypothesized monoaminergic gene variants may moderate MPH effects in ASD, as in typically developing children with attention-deficit/hyperactivity disorder. Genotype data were available for 64 children with ASD and hyperactivity who were exposed to MPH during a 1-week safety/tolerability lead-in phase and 58 who went on to be randomized to placebo and three doses of MPH during a 4-week blinded, crossover study. Outcome measures included the Clinical Global Impression-Improvement (CGI-I) scale and the Aberrant Behavior Checklist (ABC-hyperactivity index). A total of 14 subjects discontinued the study because of MPH side effects. Subjects were genotyped for variants in DRD1-DRD5, ADRA2A, SLC6A3, SLC6A4, MAOA and MAOB, and COMT. Forty-nine percent of the sample met positive responder criteria. In this modest but relatively homogeneous sample, significant differences by DRD1 (P=0.006), ADRA2A (P<0.02), COMT (P<0.04), DRD3 (P<0.05), DRD4 (P<0.05), SLC6A3 (P<0.05) and SLC6A4 (P<0.05) genotypes were found for responders versus non-responders. Variants in DRD2 (P<0.001) and DRD3 (P<0.04) were associated with tolerability in the 14 subjects who discontinued the trial. For this first MPH pharmacogenetic study in children with ASD, multiple monoaminergic gene variants may help explain individual differences in MPH's efficacy and tolerability.

Interventions for attention problems after pediatric traumatic brain injury: what is the evidence?

OBJECTIVE

To gain an understanding of the current state of the evidence for management of attention problems after traumatic brain injury (TBI) in children, determine gaps in the literature, and make recommendations for future research. TYPE: Focused systematic review.

LITERATURE SURVEY

PubMed/Medline and PsychINFO databases were searched for relevant articles published in English during the last 20 years. Keywords included "attention" "attention deficit and disruptive behavior disorders," and "brain injuries." Studies were limited to children.

METHODOLOGY

Titles were examined first and eliminated based on lack of relevancy to attention problems after brain injury in children. This was followed by an abstract and full text review. Article quality was determined based on the US Preventative Services Task Force recommendations for evidence grading.

SYNTHESIS

Four pharmacologic and 10 cognitive therapy intervention studies were identified. These studies varied in level of evidence quality but were primarily nonrandomized or cohort studies.

CONCLUSIONS

There are studies that demonstrate benefits of varying pharmacologic and cognitive therapies for the management of attention problems after TBI. However, there is a paucity of evidence available to definitively guide management of attention problems after pediatric TBI. Larger randomized, controlled trials and multicenter studies are needed to elucidate optimal treatment strategies in this population.

Association of a carboxylesterase 1 polymorphism with appetite reduction in children and adolescents with attention-deficit/hyperactivity disorder treated with methylphenidate

Carboxylesterase 1 is the enzyme involved in methylphenidate (MPH) metabolism. The aim of this study was to evaluate the association between a -75 T>G polymorphism and appetite reduction in children with attention-deficit/hyperactivity disorder (ADHD). A sample of 213 children with ADHD was investigated. The primary outcome was appetite reduction measured by the Barkley Stimulant Side Effect Rating Scale applied at baseline, at 1 and 3 months of treatment. MPH doses were augmented until no further clinical improvement or significant adverse events occurred. The G allele presented a trend for association with appetite reduction scores (P=0.05). A significant interaction between the G allele and treatment over time for appetite reduction scores was also observed (P=0.03). The G allele carriers presented a higher risk for appetite reduction worsening when compared with T allele homozygotes (odds ratio=3.47, P=0.01). The present results suggest an influence of carboxylesterase 1 -75 T>G polymorphism on the worsening of appetite reduction with MPH treatment in youths with ADHD.

Long-acting methylphenidate formulations in the treatment of attention-deficit/hyperactivity disorder: a systematic review of head-to-head studies

BACKGROUND

The stimulant methylphenidate (MPH) has been a mainstay of treatment for attention-deficit/hyperactivity disorder (ADHD) for many years. Owing to the short half-life and the issues associated with multiple daily dosing of immediate-release MPH formulations, a new generation of long-acting MPH formulations has emerged. Direct head-to-head studies of these long-acting MPH formulations are important to facilitate an evaluation of their comparative pharmacokinetics and efficacy; however, to date, relatively few head-to-head studies have been performed.The objective of this systematic review was to compare the evidence available from head-to-head studies of long-acting MPH formulations and provide information that can guide treatment selection.

METHODS

A systematic literature search was conducted in MEDLINE and PsycINFO in March 2012 using the MeSH terms: attention deficit disorder with hyperactivity/drug therapy; methylphenidate/therapeutic use and All Fields: Concerta; Ritalin LA; OROS and ADHD; Medikinet; Equasym XL and ADHD; long-acting methylphenidate; Diffucaps and ADHD; SODAS and methylphenidate. No filters were applied and no language, publication date or publication status limitations were imposed. Articles were selected if the title indicated a comparison of two or more long-acting MPH preparations in human subjects of any age; non-systematic review articles and unpublished data were not included.

RESULTS

Of 15,295 references returned in the literature search and screened by title, 34 articles were identified for inclusion: nine articles from pharmacokinetic studies (nine studies); nine articles from laboratory school studies (six studies); two articles from randomized controlled trials (two studies); three articles from switching studies (two studies) and three articles from one observational study.

CONCLUSIONS

Emerging head-to-head studies provide important data on the comparative efficacy of the formulations available. At a group level, efficacy across the day generally follows the pharmacokinetic profile of the MPH formulation. No formulation is clearly superior to another; careful consideration of patient needs and subtle differences between formulations is required to optimize treatment. For patients achieving suboptimal symptom control, switching long-acting MPH formulations may be beneficial. When switching formulations, it is usually appropriate to titrate the immediate-release component of the formulation; a limitation of current studies is a focus on total daily dose rather than equivalent immediate-release components. Further studies are necessary to provide guidance in clinical practice, particularly in the treatment of adults and pre-school children and the impact of comorbidities and symptom severity on treatment response.

The association of a novel haplotype in the dopamine transporter with preschool age posttraumatic stress disorder

OBJECTIVE

Significant evidence supports a genetic contribution to the development of posttraumatic stress disorder (PTSD). Three previous studies have demonstrated an association between PTSD and the nine repeat allele of the 3' untranslated region (3'UTR) variable number tandem repeat (VNTR) in the dopamine transporter (DAT, rs28363170). Recently a novel, functionally significant C/T single-nucleotide polymorphism (SNP) in the 3'UTR (rs27072) with putative interactions with the 3'VNTR, has been identified. To provide enhanced support for the role of DAT and striatal dopamine regulation in the development of PTSD, this study examined the impact of a haplotype defined by the C allele of rs27072 and the nine repeat allele of the 3'VNTR on PTSD diagnosis in young trauma-exposed children.

METHODS

DAT haplotypes were determined in 150 trauma-exposed 3-6 year-old children. PTSD was assessed with a semistructured interview. After excluding double heterozygotes, analysis was performed on 143 total subjects. Haplotype was examined in relation to categorical and continuous measures of PTSD, controlling for trauma type and race. Additional analysis within the two largest race categories was performed, as other means of controlling for ethnic stratification were not available.

RESULTS

The number of haplotypes (0, 1, or 2) defined by the presence of the nine repeat allele of rs28363170 (VNTR in the 3'UTR) and the C allele of rs27072 (SNP in the 3'UTR) was significantly associated with both the diagnosis of PTSD and total PTSD symptoms. Specifically, children with one or two copies of the haplotype had significantly more PTSD symptoms and were more likely to be diagnosed with PTSD than were children without this haplotype.

CONCLUSIONS

These findings extend previous findings associating genetic variation in the DAT with PTSD. The association of a haplotype in DAT with PTSD provides incremental traction for a model of genetic vulnerability to PTSD, a specific underlying mechanism implicating striatal dopamine regulation, and insight into potential future personalized interventions.

Stimulant side effects and inverted-U: implications for ADHD guidelines

OBJECTIVE

To review literature relevant to a possible prediction of stimulant side effects in attention deficit hyperactivity disorder (ADHD), with implications for guidelines.

METHOD

Recent literature on inverted-U effects of dopamine in the prefrontal cortex (PFC), default mode processing, and motor circuits relevant to stimulant side effects is reviewed.

RESULTS

The literature on inverted-U effects in the PFC suggests that catechol-O-methyltransferase (COMT) Met versus Val polymorphisms may predict excess dopaminergic effects, including headache and introversion in Met/Met subjects, but therapeutic effects in Val/Val subjects, while dopamine transporter polymorphisms may predict motor side effects. In particular, an understanding of 'inverted-U' effects helps to explain why some children may experience side effects while others show improvements at similar dose ranges.

CONCLUSION

Genetic prediction of stimulant side effects should be investigated, particularly given recent controversies in relation to National Health and Medical Research Council guidelines for stimulant use. A better understanding of treatment-emergent effects will also provide a better understanding of therapeutic effects.

Systematic reviews of animal models: methodology versus epistemology

Systematic reviews are currently favored methods of evaluating research in order to reach conclusions regarding medical practice. The need for such reviews is necessitated by the fact that no research is perfect and experts are prone to bias. By combining many studies that fulfill specific criteria, one hopes that the strengths can be multiplied and thus reliable conclusions attained. Potential flaws in this process include the assumptions that underlie the research under examination. If the assumptions, or axioms, upon which the research studies are based, are untenable either scientifically or logically, then the results must be highly suspect regardless of the otherwise high quality of the studies or the systematic reviews. We outline recent criticisms of animal-based research, namely that animal models are failing to predict human responses. It is this failure that is purportedly being corrected via systematic reviews. We then examine the assumption that animal models can predict human outcomes to perturbations such as disease or drugs, even under the best of circumstances. We examine the use of animal models in light of empirical evidence comparing human outcomes to those from animal models, complexity theory, and evolutionary biology. We conclude that even if legitimate criticisms of animal models were addressed, through standardization of protocols and systematic reviews, the animal model would still fail as a predictive modality for human response to drugs and disease. Therefore, systematic reviews and meta-analyses of animal-based research are poor tools for attempting to reach conclusions regarding human interventions.

A post hoc comparison of the effects of lisdexamfetamine dimesylate and osmotic-release oral system methylphenidate on symptoms of attention-deficit hyperactivity disorder in children and adolescents

INTRODUCTION

There are limited head-to-head data comparing the efficacy of long-acting amfetamine- and methylphenidate-based psychostimulants as treatments for individuals with attention-deficit hyperactivity disorder (ADHD). This post hoc analysis provides the first parallel-group comparison of the effect of lisdexamfetamine dimesylate (lisdexamfetamine) and osmotic-release oral system methylphenidate (OROS-MPH) on symptoms of ADHD in children and adolescents.

STUDY DESIGN

This was a post hoc analysis of a randomized, double-blind, parallel-group, dose-optimized, placebo-controlled, phase III study.

SETTING

The phase III study was carried out in 48 centres across ten European countries.

PATIENTS

The phase III study enrolled children and adolescents (aged 6-17 years) who met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria for a primary diagnosis of ADHD and who had a baseline ADHD Rating Scale IV (ADHD-RS-IV) total score of 28 or higher.

INTERVENTION

Eligible patients were randomized (1:1:1) to receive a once-daily, optimized dose of lisdexamfetamine (30, 50 or 70 mg/day), placebo or OROS-MPH (18, 36 or 54 mg/day) for 7 weeks.

MAIN OUTCOME MEASURES

In this post hoc analysis, efficacy was assessed using the ADHD-RS-IV and Clinical Global Impressions-Improvement (CGI-I) scale. Responders were defined as those achieving at least a 30% reduction from baseline in ADHD-RS-IV total score and a CGI-I score of 1 (very much improved) or 2 (much improved). The proportion of patients achieving an ADHD-RS-IV total score less than or equal to the mean for their age (based on normative data) was also determined. Endpoint was the last on-treatment visit with a valid assessment. Safety assessments included treatment-emergent adverse events (TEAEs) and vital signs.

RESULTS

Of the 336 patients randomized, 332 were included in the safety population, 317 were included in the full analysis set and 196 completed the study. The mean (standard deviation) ADHD-RS-IV total score at baseline was 40.7 (7.31) for lisdexamfetamine, 41.0 (7.14) for placebo and 40.5 (6.72) for OROS-MPH. The least-squares (LS) mean change (standard error) in ADHD-RS-IV total score from baseline to endpoint was -24.3 (1.16) for lisdexamfetamine, -5.7 (1.13) for placebo and -18.7 (1.14) for OROS-MPH. The difference between lisdexamfetamine and OROS-MPH in LS mean change (95% confidence interval [CI]) in ADHD-RS-IV total score from baseline to endpoint was statistically significant in favour of lisdexamfetamine (-5.6 [-8.4 to -2.7]; p < 0.001). The difference between lisdexamfetamine and OROS-MPH in the percentage of patients (95% CI) with a CGI-I score of 1 or 2 at endpoint was 17.4 (5.0-29.8; p < 0.05; number needed to treat [NNT] 6), and the difference in the percentage of patients (95% CI) achieving at least a 30% reduction in ADHD-RS-IV total score and a CGI-I score of 1 or 2 was 18.3 (5.4-31.3; p < 0.05; NNT 6). The difference between lisdexamfetamine and OROS-MPH in the percentage of patients (95% CI) with an ADHD-RS-IV total score less than or equal to the mean for their age at endpoint was 14.0 (0.6-27.4; p = 0.050). The overall frequency of TEAEs and the frequencies of decreased appetite, insomnia, decreased weight, nausea and anorexia TEAEs were greater in patients treated with lisdexamfetamine than in those treated with OROS-MPH, whereas headache and nasopharyngitis were more frequently reported in patients receiving OROS-MPH.

CONCLUSIONS

This post hoc analysis showed that, at the doses tested, patients treated with lisdexamfetamine showed statistically significantly greater improvement in symptoms of ADHD than those receiving OROS-MPH, as assessed using the ADHD-RS-IV and CGI-I. The safety profiles of lisdexamfetamine and OROS-MPH were consistent with the known effects of stimulant medications.

Updates on treatment of attention-deficit/hyperactivity disorder: facts, comments, and ethical considerations

OPINION STATEMENT

Within the last 2 years the bulk of information on evidence based treatments in ADHD was reviewed quite intensively and new empirical studies could be added. This update reports comprehensively about actual and essential facts in the field related to brain development and sensitive periods, predictors of treatment, safety of medication, value of naturalistic studies, new drugs and complementary medicine, behavioral interventions including neurofeedback and psychosocial treatment, treatment of comorbidity, and ethical considerations including preventive aspects. The updated combination of well selected evidence based treatments (ie, pharma plus non-pharma) seems to be clinically and ethically recommended as also suggested by the European and American guidelines on ADHD.

Interaction of dopamine transporter gene and observed parenting behaviors on attention-deficit/hyperactivity disorder: a structural equation modeling approach

Emerging evidence suggests that some individuals may be simultaneously more responsive to the effects from environmental adversity and enrichment (i.e., differential susceptibility). Given that parenting behavior and a variable number tandem repeat polymorphism in the 3'untranslated region of the dopamine transporter (DAT1) gene are each independently associated with attention-deficit/hyperactivity disorder (ADHD), our goal was to evaluate the potential interactive effects of child DAT1 genotype with positive and negative parenting behaviors on childhood ADHD. We recruited an ethnically diverse sample of 150 six- to nine-year-old boys and girls with and without ADHD. Children were genotyped for a common polymorphism of the DAT1 gene, and objective counts of observed parenting behavior (i.e., negativity and praise) were obtained from a valid parent-child interaction task. Structural equation modeling was used to examine the interactive effects of DAT1 and observed parenting with a latent ADHD factor. We detected a significant interaction between observed praise and child DAT1 (coded additively), which suggested that praise was associated with increased ADHD, but only among youth with the 9/10 genotype. In addition, a marginally significant interaction between DAT1 (coded additively and recessively) and observed negativity emerged for ADHD, such that negativity was positively associated with ADHD but only for youth with the 9/9 genotype. Although differential susceptibility theory was not fully supported, these preliminary results suggest that interactive exchanges between parenting behavior and child genotype potentially contribute to the development of ADHD. Clinical implications for interactions between parenting behavior and child genotype are discussed.

Attention-deficit/hyperactivity disorder genomics: update for clinicians

Attention deficit, hyperactivity disorder (ADHD) is familial and highly heritable. Several candidate genes involved in neurotransmission have been identified, however these confer minimal risk, suggesting that for the most part, ADHD is not caused by single common genetic variants. Advances in genotyping enabling investigation at the level of the genome have led to the discovery of rare structural variants suggesting that ADHD is a genomic disorder, with potentially thousands of variants, and common neuronal pathways disrupted by numerous rare variants resulting in similar ADHD phenotypes. Heritability studies in humans also indicate the importance of epigenetic factors, and animal studies are deciphering some of the processes that confer risk during gestation and throughout the post-natal period. These and future discoveries will lead to improved diagnosis, individualized treatment, cures, and prevention. These advances also highlight ethical and legal issues requiring management and interpretation of genetic data and ensuring privacy and protection from misuse.

Animal models and conserved processes

BACKGROUND

The concept of conserved processes presents unique opportunities for using nonhuman animal models in biomedical research. However, the concept must be examined in the context that humans and nonhuman animals are evolved, complex, adaptive systems. Given that nonhuman animals are examples of living systems that are differently complex from humans, what does the existence of a conserved gene or process imply for inter-species extrapolation?

METHODS

We surveyed the literature including philosophy of science, biological complexity, conserved processes, evolutionary biology, comparative medicine, anti-neoplastic agents, inhalational anesthetics, and drug development journals in order to determine the value of nonhuman animal models when studying conserved processes.

RESULTS

Evolution through natural selection has employed components and processes both to produce the same outcomes among species but also to generate different functions and traits. Many genes and processes are conserved, but new combinations of these processes or different regulation of the genes involved in these processes have resulted in unique organisms. Further, there is a hierarchy of organization in complex living systems. At some levels, the components are simple systems that can be analyzed by mathematics or the physical sciences, while at other levels the system cannot be fully analyzed by reducing it to a physical system. The study of complex living systems must alternate between focusing on the parts and examining the intact whole organism while taking into account the connections between the two. Systems biology aims for this holism. We examined the actions of inhalational anesthetic agents and anti-neoplastic agents in order to address what the characteristics of complex living systems imply for inter-species extrapolation of traits and responses related to conserved processes.

CONCLUSION

We conclude that even the presence of conserved processes is insufficient for inter-species extrapolation when the trait or response being studied is located at higher levels of organization, is in a different module, or is influenced by other modules. However, when the examination of the conserved process occurs at the same level of organization or in the same module, and hence is subject to study solely by reductionism, then extrapolation is possible.

Insights into multimodal imaging classification of ADHD

Attention deficit hyperactivity disorder (ADHD) currently is diagnosed in children by clinicians via subjective ADHD-specific behavioral instruments and by reports from the parents and teachers. Considering its high prevalence and large economic and societal costs, a quantitative tool that aids in diagnosis by characterizing underlying neurobiology would be extremely valuable. This provided motivation for the ADHD-200 machine learning (ML) competition, a multisite collaborative effort to investigate imaging classifiers for ADHD. Here we present our ML approach, which used structural and functional magnetic resonance imaging data, combined with demographic information, to predict diagnostic status of individuals with ADHD from typically developing (TD) children across eight different research sites. Structural features included quantitative metrics from 113 cortical and non-cortical regions. Functional features included Pearson correlation functional connectivity matrices, nodal and global graph theoretical measures, nodal power spectra, voxelwise global connectivity, and voxelwise regional homogeneity. We performed feature ranking for each site and modality using the multiple support vector machine recursive feature elimination (SVM-RFE) algorithm, and feature subset selection by optimizing the expected generalization performance of a radial basis function kernel SVM (RBF-SVM) trained across a range of the top features. Site-specific RBF-SVMs using these optimal feature sets from each imaging modality were used to predict the class labels of an independent hold-out test set. A voting approach was used to combine these multiple predictions and assign final class labels. With this methodology we were able to predict diagnosis of ADHD with 55% accuracy (versus a 39% chance level in this sample), 33% sensitivity, and 80% specificity. This approach also allowed us to evaluate predictive structural and functional features giving insight into abnormal brain circuitry in ADHD.