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

Possible effect of norepinephrine transporter polymorphisms on methylphenidate-induced changes in neuropsychological function in attention-deficit hyperactivity disorder

Background

Dysregulation of noradrenergic system may play important roles in pathophysiology of attention-deficit/hyperactivity disorder (ADHD). We examined the relationship between polymorphisms in the norepinephrine transporter SLC6A2 gene and attentional performance before and after medication in children with ADHD.

Methods

Fifty-three medication-naïve children with ADHD were genotyped and evaluated using the continuous performance test (CPT). After 8-weeks of methylphenidate treatment, these children were evaluated by CPT again. We compared the baseline CPT measures and the post-treatment changes in the CPT measures based on the G1287A and the A-3081T polymorphisms of SLC6A2.

Results

There was no significant difference in the baseline CPT measures associated with the G1287A or A-3081T polymorphisms. After medication, however, ADHD subjects with the G/G genotype at the G1287A polymorphism showed a greater decrease in the mean omission error scores (p = 0.006) than subjects with the G/A or A/A genotypes, and subjects with the T allele at the A-3081T polymorphism (T/T or A/T) showed a greater decrease in the mean commission error scores (p = 0.003) than those with the A/A genotypes.

Conclusions

Our results provide evidence for the possible role of the G1287A and A-3081T genotypes of SLC6A2 in methylphenidate-induced improvement in attentional performance and support the noradrenergic hypothesis for the pathophysiology of ADHD.

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

OBJECTIVE

Because of significant individual variability in attention-deficit/hyperactivity disorder (ADHD) medication response, there is increasing interest in identifying genetic predictors of treatment effects. This study examined the role of four catecholamine-related candidate genes in moderating methylphenidate (MPH) dose-response.

METHOD

Eighty-nine stimulant-naive children with ADHD 7 to 11 years old participated in a randomized, double-blind, crossover trial of long-acting MPH. Parents and teachers assessed each child's response on placebo and three MPH dosage levels using the Vanderbilt ADHD rating scales. Children were genotyped for polymorphisms in the 3' untranslated region of dopamine transporter (DAT), exon 3 on dopamine receptor D(4) (DRD4), codon 158 on catechol-O-methyltransferase, and the adrenergic α(2A)-receptor promoter. Linear mixed models evaluated gene, dose (milligrams per kilogram per day), and gene-by-dose effects on inattentive and hyperactive-impulsive domain outcomes.

RESULTS

The most statistically significant gene-by-dose interactions were observed on hyperactive-impulsive symptoms for DRD4 and DAT polymorphisms, with participants lacking the DAT 10-repeat allele showing greater improvements in symptoms with increasing dose compared with 10-repeat carriers (p = .008) and those lacking the DRD4 4-repeat allele showing less improvement across MPH doses compared with 4-repeat carriers (p = 0.02).

CONCLUSIONS

This study suggests that DAT and DRD4 polymorphisms may be associated with individual variability in MPH dose-response, although further research in larger samples is required to confirm these findings and their clinical utility.

CLINICAL TRIAL REGISTRATION INFORMATION

Response Variability in Children with Attention-Deficit/Hyperactivity Disorder (ADHD); http://www.clinicaltrials.gov; NCT01238822.

Val/Val genotype of brain-derived neurotrophic factor (BDNF) Val⁶⁶Met polymorphism is associated with a better response to OROS-MPH in Korean ADHD children

Research on psychostimulants, analysis of animal models and genetic association studies all suggest that the brain-derived neurotrophic factor gene (BDNF) may be a good candidate for pharmacogenetic studies of attention deficit hyperactivity disorder (ADHD). Yet to date there have been no pharmacogenetic studies of BDNF in ADHD. A total of 102 drug-naive ADHD children (8.7±2.1 yr) were treated with osmotic release oral system-methylphenidate (OROS-MPH) for 12 wk, and four kinds of response criteria were applied, based first, on a combined threshold of the ADHD Rating Scale - IV (ARS) and the Clinical Global Impression - Improvement scale (CGI-I); second, on scores of 1 or 2 vs. 3-7 on the CGI - Severity scale; third, on a >50% reduction in ARS scores; and fourth, on satisfaction of all of the aforementioned criteria. The Val⁶⁶Met polymorphism of BDNF and six single nucleotide polymorphisms from the SLC6A2, ADRA2A and NTF-3 genes were tested for association with each criterion. Relative to other genotypes, homozygosity for the Val allele of the BDNF Val⁶⁶Met polymorphism was associated with a greater relative frequency of good response under all four response criteria (after controlling for baseline ARS score, age, gender, final dose (mg/kg) of OROS-MPH at 12 wk, and level of academic functioning). This association was significant at the uncorrected level for the first and third response criteria (p=0.013 and p=0.018, respectively) and significant at a Bonferroni-corrected level for the second and fourth response criteria (p=0.0002, p=0.0003, respectively). Our findings support an association between homozygosity for the Val allele of BDNF and better response to OROS-MPH in Korean ADHD children as assessed by four different response criteria.

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.

Human serotonin transporter gene (SLC6A4) variants: their contributions to understanding pharmacogenomic and other functional G×G and G×E differences in health and disease

Recent major findings from studies of SLC6A4 and its corresponding protein, the serotonin (5-HT) transporter (SERT) in humans, rodents and non-human primates indicate that combinations of SLC6A4 non-coding 5', 3' UTRs and intronic regions plus coding variants acting together can change 5HT transport as much as 40-fold in vitro. In vivo, SLC6A4 variants in humans and other species lead to marked physiological changes, despite mitigating neurodevelopmental adaptations in 5-HT receptors plus compensatory alterations in 5-HT synthesis and metabolism. Polymorphisms in SLC6A4 are associated with differences in emotional, endocrine, and personality characteristics as well as many diseases. This gene, in combinations with gene×gene (G×G) and gene×environment (G×E) interactions nonetheless remains incompletely understood, with some association findings remaining controversial. Considering its primary importance in the regulation and function of the entire serotonergic system (as evidenced by the consequences of SERT-mediated reuptake inhibition by SRIs like fluoxetine in humans and of genetically engineered changes in mice and rats), it seems likely that SLC6A4 and SERT will remain areas of high interest in our field's attempts to better understand and treat 5-HT-related disorders.

Possible association of norepinephrine transporter -3081(A/T) polymorphism with methylphenidate response in attention deficit hyperactivity disorder

Background

Attention-deficit/hyperactivity disorder (ADHD) is a heritable disorder characterized by symptoms of inattention and/or hyperactivity/impulsivity. Methylphenidate (MPH) has been shown to block the norepinephrine transporter (NET), and genetic investigations have demonstrated that the norepinephrine transporter gene (SLC6A2) is associated with ADHD. The aims of this study were to examine the association of the SLC6A2 -3081(A/T) and G1287A polymorphisms with MPH response in ADHD.

Methods

This study enrolled 112 children and adolescents with ADHD. A response criterion was defined based on the Clinical Global Impression-Improvement (CGI-I) score, and the ADHD Rating Scale-IV (ARS) score was also assessed at baseline and 8 weeks after MPH treatment.

Results

We found that the subjects who had the T allele as one of the alleles (A/T or T/T genotypes) at the -3081(A/T) polymorphism showed a better response to MPH treatment than those with the A/A genotype as measured by the CGI-I. We also found a trend towards a difference in the change of the total ARS scores and hyperactivity/impulsivity subscores between subjects with and without the T allele. No significant association was found between the genotypes of the SLC6A2 G1287A polymorphism and response to ADHD treatment.

Conclusion

Our findings provide evidence for the involvement of the -3081(A/T) polymorphism of SLC6A2 in the modulation of the effectiveness of MPH treatment in ADHD.