Dimorphic association of dopaminergic transporter gene variants with treatment outcome: Pilot study in Indian ADHD probands

Evaluation of SLC6A2 and CYP2D6 polymorphisms' effects on atomoxetine treatment in attention deficit and hyperactivity disorder

BACKGROUND

There is insufficient replicated data to establish a relationship between the polymorphisms of SLC6A2 and CYP2D6 and the treatment responses of atomoxetine (ATX) in ADHD. We focused on evaluating the effect of top-line single nucleotide polymorphisms (SNPs) in SLC6A2 and CYP2D6 on the ATX treatment response in attention deficit and hyperactivity disorder (ADHD).

METHODS

Of 160 patient records, 34 patients who met the inclusion criteria were evaluated to determine the relationship between genotypes of ten SNPs (six of SLC6A2 and four of CYP2D6) and ATX treatment response. Additionally, the connection between SNPs of CYP2D6 and the severity of side effects associated with ATX was analyzed in 37 patients, including the 34 study patients, and three patients discontinued because of ATX-dependent side effects.

RESULTS

All six polymorphisms we studied in SLC6A2 were associated with the treatment response of ATX. Clinical improvement in oppositional defiant disorder symptoms of patients with ADHD was only observed in carriers of the homozygous "C" allele of rs3785143 (podd = 0.026). We detected an association between higher CGI-side-effect severity scores and the "TT" genotype of rs1065852 polymorphism in CYP2D6 (p = 0.043).

CONCLUSIONS

The findings of this study suggest that genotypes of polymorphisms within the SLC6A2 and CYP2D6 may play an influential role in treatment response or the severity of side effects associated with ATX in ADHD patients.

Glutamate receptor genetic variants affected peripheral glutamatergic transmission and treatment induced improvement of Indian ADHD probands

Attention deficit hyperactivity disorder (ADHD), a childhood-onset neurobehavioral disorder, often perturbs scholastic achievement and peer-relationship. The pivotal role of glutamate (Glu) in learning and memory indicated an influence of Glu in ADHD, leading to the exploration of Glu in different brain regions of ADHD subjects. We for the first time analyzed GluR genetic variations, Glu levels, as well as expression of Glu receptors (GluR) in the peripheral blood of eastern Indian ADHD probands to find out the relevance of Glu in ADHD prognosis. After obtaining informed written consent for participation, peripheral blood was collected for analyzing the genetic variants, Glu level, and expression of target genes. Since ADHD probands are often treated with methylphenidate or atomoxetine for providing symptomatic remediation, we have also tested post-therapeutic improvement in the ADHD trait scores in the presence of different GluR genotypes. Two variants, GRM7 rs3749380 "T" and GRIA1 rs2195450 "C", exhibited associations with ADHD (P ≤ 0.05). A few GluR genetic variants showed significant association with higher trait severity, low IQ, lower plasma Glu level, down-regulated GluR mRNA expression, and poor response to medications. This indicates that down-regulated glutamatergic system may have an effect on ADHD etiology and treatment efficacy warranting further in-depth investigation.

Post-treatment symptomatic improvement of the eastern Indian ADHD probands is influenced by CYP2D6 genetic variations

OBJECTIVES

Symptomatic remediation from attention deficit hyperactivity disorder (ADHD)-associated traits is achieved by treatment with methylphenidate (MPH)/atomoxetine (ATX). We have analyzed the association of functional CYP2D6 variations, rs1065852, rs3892097, rs1135840, and rs1058164, with ADHD in the Indian subjects.

METHODS

Subjects were recruited following the Diagnostic and Statistical Manual for Mental Disorders. Trait scores were obtained from the Conner's Parents Rating Scale-Revised. After obtaining informed consent, blood was collected for DNA isolation, and genotyping was performed by PCR or TaqMan-based methods. Probands were treated with MPH or ATX based on age, symptoms, and drug availability. Treatment outcome was assessed using a structured questionnaire. Data obtained was analyzed to identify the association of CYP2D6 variations and the SLC6A3 rs28363170 with the treatment outcome.

RESULTS

The frequency of rs1135840 "G" and rs1065852 "G" was higher in the male ADHD probands. Bias in parental transmission (p=0.007) and association with higher trait scores were observed for rs1065852 "A". Independent influence of rs1065852 on ADHD was also observed. Probands carrying rs1065852 'GG', rs1135840 'CG', and rs28363170 10R exhibited significant symptomatic improvement with MPH, while probands with rs1135840 'CC' and rs28363170 9R showed improvement after ATX treatment.

CONCLUSIONS

ADHD probands having specific CYP2D6 genetic variations respond differentially to pharmaceutical intervention.

Personalizing atomoxetine dosing in children with ADHD: what can we learn from current supporting evidence

PURPOSE

There is marked heterogeneity in treatment response of atomoxetine in patients with attention deficit/hyperactivity disorder (ADHD), especially for the pediatric population. This review aims to evaluate current evidence to characterize the dose-exposure relationship, establish clinically relevant metrics for systemic exposure to atomoxetine, define a therapeutic exposure range, and to provide a dose-adaptation strategy before implementing personalized dosing for atomoxetine in children with ADHD.

METHODS

A comprehensive search was performed across electronic databases (PubMed and Embase) covering the period of January 1, 1985 to July 10, 2022, to summarize recent advances in the pharmacokinetics, pharmacogenomics/pharmacogenetics (PGx), therapeutic drug monitoring (TDM), physiologically based pharmacokinetics (PBPK), and population pharmacokinetics (PPK) of atomoxetine in children with ADHD.

RESULTS

Some factors affecting the pharmacokinetics of atomoxetine were summarized, including food, CYP2D6 and CYP2C19 phenotypes, and drug‒drug interactions (DDIs). The association between treatment response and genetic polymorphisms of genes encoding pharmacological targets, such as norepinephrine transporter (NET/SLC6A2) and dopamine β hydroxylase (DBH), was also discussed. Based on well-developed and validated assays for monitoring plasma concentrations of atomoxetine, the therapeutic reference range in pediatric patients with ADHD proposed by several studies was summarized. However, supporting evidence on the relationship between systemic atomoxetine exposure levels and clinical response was far from sufficient.

CONCLUSION

Personalizing atomoxetine dosage may be even more complex than anticipated thus far, but elucidating the best way to tailor the non-stimulant to a patient's individual need will be achieved by combining two strategies: detailed research in linking the pharmacokinetics and pharmacodynamics in pediatric patients, and better understanding in nature and causes of ADHD, as well as environmental stressors.

Kainate receptor subunit 1 (GRIK1) risk variants and GRIK1 deficiency were detected in the Indian ADHD probands

Executive dysfunctions caused by structural and functional abnormalities of the prefrontal cortex were reported in patients with Attention deficit hyperactivity disorder (ADHD). Owing to a higher expression of the glutamate ionotropic receptor kainate type subunit 1 (GluK1), encoded by the GRIK1 gene, in brain regions responsible for learning and memory, we hypothesized that GRIK1 might have a role in ADHD. GRIK1 variants rs363504 and rs363538, affecting the receptor function, were analyzed by case-control and family-based methods to identify the association with ADHD. The impact of these variants on ADHD-associated traits and pharmacological intervention were also analyzed. GRIK1 expression was quantified in the peripheral blood. The probands and their fathers had a higher frequency of rs363504 'CC' and rs363538 'CA' genotypes. Family-based investigation revealed maternal over transmission of rs363504 'C' and rs363538 'A' alleles to the probands. Quantitative trait analysis exhibited an association of rs363504 'TT' and rs363538 'AA' genotypes with higher hyperactivity scores of the probands. In the presence of rs363504 'TT' and rs363538 'CC' genotypes, MPH treatment improved hyperactivity and inattention, respectively. GRIK1 expression was significantly downregulated in the probands. We infer that GRIK1 affects ADHD etiology, warranting further in-depth investigation involving a larger cohort and more functional variants.

Role of the norepinephrine transporter polymorphisms in atomoxetine treatment: From response to side effects in children with ADHD

OBJECTIVE

Atomoxetine (ATX), one of the most commonly used drugs after stimulants in attention deficit hyperactivity disorder (ADHD) treatment, is an inhibitor of the norepinephrine transporter (NET/SLC6A2), which is also associated with the etiology of ADHD. In this study, we aimed to investigate the effect of NET gene polymorphisms on response to ATX treatment and to find the answers to the questions about whether there is a relationship between the severity of the disorder and the observed side effects in children with ADHD.

METHOD

About 100 children with ADHD and 80 healthy controls (HCs) were included in this study. The dose of ATX was started at 0.5 mg/kg/day and titrated at 1.2 mg/kg/day. Response to treatment of 78 patients was evaluated 2 months after the beginning of the treatment. After whole blood samples were obtained, DNAs were isolated, and samples were stored at -80°C. Two single-nucleotide polymorphisms (SNPs) (rs12708954 and rs3785143) were analyzed by real-time quantitative PCR (qRT-PCR).

RESULTS

The patients with both rs12708954 and rs3785143 heterozygous genotype had better treatment response and more side effects than patients with wild type. There was not found any association between any of the investigated NET polymorphisms and ADHD severity.

CONCLUSION

It was, however, found that the NET rs12708954 and rs3785143 genotypes affect the treatment response to ATX in our study; thus, further studies with a large population are needed to understand the effects of NET polymorphisms on treatment, side effects, and also the severity of ADHD.

Functional SLC6A3 polymorphisms differentially affect autism spectrum disorder severity: a study on Indian subjects

Imbalance in dopamine (DA) signaling is proposed to play a potential role in the etiology of Autism spectrum disorder (ASD) since, as a neuromodulator, DA regulates executive function, motor activity, social peering, attention as well as perception and subjects with ASD often exhibit deficit in these traits. Level of DA in the synaptic cleft is maintained by dopamine transporter (DAT) and hence, to identify the role of DAT in ASD, we have analyzed four functional genetic variants, rs28363170, rs3836790, rs2652511, rs27072, in nuclear families with ASD probands. Subjects were diagnosed based on Diagnostic and Statistical Manual for Mental Disorders and trait severity was assessed by Childhood Autism Rating Scale 2-Standard test. Informed written consent was obtained from the parents/care givers before recruitment followed by collection of peripheral blood for genomic DNA isolation. Target sites were investigated by PCR-based methods and data obtained was analyzed by population- as well as family-based statistical methods. Case-control analysis revealed significant higher frequencies of 9 repeat (9R) and 5 repeat (5R) alleles of rs28363170 and rs3836790 respectively in the ASD probands. Family-based analysis showed statistically significant higher paternal transmission of rs28363170 9R and rs2652511 T alleles. In the presence of rs28363170 9R, rs27072 C, rs3836790 6R6R, and rs2652511 CC variants, trait scores were higher. Studied variants showed independent as well as interactive effects, which varied based on gender of the probands. We infer that altered DA availability mediated through DAT may affect autistic traits warranting further in depth investigation in the field.

SLC6A3 polymorphism and response to methylphenidate in children with ADHD: A systematic review and meta-analysis

Methylphenidate (MPH) is the most commonly used treatment for attention-deficit hyperactivity disorder (ADHD) in children. However, the response to MPH is not similar in all patients. This meta-analysis investigated the potential role of SLC6A3 polymorphisms in response to MPH in children with ADHD. Clinical trials or naturalistic studies were selected from electronic databases. A meta-analysis was conducted using a random-effects model. Cohen's d effect size and 95% confidence intervals (CIs) were determined. Sensitivity analysis and meta-regression were performed. Q-statistic and Egger's tests were conducted to evaluate heterogeneity and publication bias, respectively. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to assess the quality of evidence. Sixteen studies with follow-up periods of 1-28 weeks were eligible. The mean treatment acceptability of MPH was 97.2%. In contrast to clinical trials, the meta-analysis of naturalistic studies indicated that children without 10/10 repeat carriers had better response to MPH (Cohen's d: -0.09 and 0.44, respectively). The 9/9 repeat polymorphism had no effect on the response rate (Cohen's d: -0.43). In the meta-regression, a significant association was observed between baseline severity of ADHD, MPH dosage, and combined type of ADHD in some genetic models. Sensitivity analysis indicated the robustness of our findings. No publication bias was observed in our meta-analysis. The GRADE evaluations revealed very low levels of confidence for each outcome of response to MPH. The results of clinical trials and naturalistic studies regarding the effect size between different polymorphisms of SLC6A3 were contradictory. Therefore, further research is recommended.