Specific Genes Associated with Adverse Events of Methylphenidate Use in the Pediatric Population: A Systematic Literature Review

Molecular Characterisation of the Mechanism of Action of Stimulant Drugs Lisdexamfetamine and Methylphenidate on ADHD Neurobiology: A Review

Attention-deficit/hyperactivity disorder (ADHD) is a common childhood-onset neurodevelopmental disorder characterised by persistent inattention, hyperactivity and impulsivity. Moreover, ADHD is commonly associated with other comorbid diseases (depression, anxiety, bipolar disorder, etc.). The ADHD symptomatology interferes with subject function and development. The treatment of ADHD requires a multidisciplinary approach based on a combination of non-pharmacological and pharmacological treatments with the aim of ameliorating the symptomatology; among first-line pharmacological treatments are stimulants [such as methylphenidate (MPH) and lisdexamfetamine dimesylate (LDX)]. In this review we explored recent ADHD- and stimulants-related literature, with the aim of compiling available descriptions of molecular pathways altered in ADHD, and molecular mechanisms of current first-line stimulants MPH and LDX. While conducting the narrative review, we applied structured search strategies covering PubMed/MEDLINE database and performed handsearching of reference lists on the results of those searches. The aetiology and pathophysiology of ADHD are incompletely understood; both genetic and environmental factors have been associated with the disorder and its grade of burden, and also the relationship between the molecular mechanisms of pharmacological treatments and their clinical implications. The lack of comprehensive understanding of the underlying molecular pathology makes both the diagnosis and treatment difficult. Few published studies evaluating molecular data on the mechanism of action (MoA) of MPH and LDX on ADHD are available and most of them are based on animal models. Further studies are necessary to improve the knowledge of ADHD pathophysiology and how the MoAs of MPH and LDX differentially modulate ADHD pathophysiology and control ADHD symptomatology.

Toward Precision Medicine in ADHD

Attention-Deficit Hyperactivity Disorder (ADHD) is a complex and heterogeneous neurodevelopmental condition for which curative treatments are lacking. Whilst pharmacological treatments are generally effective and safe, there is considerable inter-individual variability among patients regarding treatment response, required dose, and tolerability. Many of the non-pharmacological treatments, which are preferred to drug-treatment by some patients, either lack efficacy for core symptoms or are associated with small effect sizes. No evidence-based decision tools are currently available to allocate pharmacological or psychosocial treatments based on the patient's clinical, environmental, cognitive, genetic, or biological characteristics. We systematically reviewed potential biomarkers that may help in diagnosing ADHD and/or stratifying ADHD into more homogeneous subgroups and/or predict clinical course, treatment response, and long-term outcome across the lifespan. Most work involved exploratory studies with cognitive, actigraphic and EEG diagnostic markers to predict ADHD, along with relatively few studies exploring markers to subtype ADHD and predict response to treatment. There is a critical need for multisite prospective carefully designed experimentally controlled or observational studies to identify biomarkers that index inter-individual variability and/or predict treatment response.

Associations between CES1 variants and dosing and adverse effects in children taking methylphenidate

BACKGROUND

Methylphenidate is the most prescribed stimulant to treat attention deficit-hyperactivity disorder (ADHD). Despite its widespread usage, a fair proportion of children are classified as non-responders to the medication. Variability in response and occurrence of adverse events with methylphenidate use may be due to several factors, including drug-drug interactions as well as pharmacogenetic differences resulting in pharmacokinetic and/or pharmacodynamic variances within the general population. The objective of this study was to analyze the effect of carboxylesterase 1 (CES1) variants on the frequency of adverse effects and dosing requirements of methylphenidate in children with ADHD.

METHODS

This was a retrospective cohort study of children and adolescents who met the inclusion criteria and had a routine visit during the enrollment period were invited to participate. Inclusion criteria included: ADHD diagnosis by a healthcare provider, between 6 and 16 years of age at the time of permission/assent, had not previously been prescribed methylphenidate, and treatment with any methylphenidate formulation for at least three consecutive months. Three months of records were reviewed in order to assess changes in dose and frequency of discontinuing methylphenidate. Participants' ADHD symptoms, medication response, adverse effects, select vitals, and dose were extracted from the electronic health record. Saliva samples were collected by trained study coordinators. Haplotypes were assigned based on copy number in different portions of the CES1 gene. Due to limited numbers, diplotypes (combinations of two haplotypes) were grouped for analysis as CES1A1/CES1A1, CES1A1/CES1A1c and CES1A1c/CES1A1c.

RESULTS

A total of 99 participants (n = 30 female; n = 69 male) had both clinical data and CES1 sequencing data, with an average age of 7.7 years old (range 3-15 years). The final weight-based dose in all individuals was 0.79 mg/kg/day. The most common adverse effects reported were decreased appetite (n = 47), weight loss (n = 24), and sleep problems (n = 19). The mean final weight-based dose by haplotype was 0.92 mg/kg for CES1A2/CES1A2, 0.81 mg/kg for CES1A2/CES1P1, and 0.78 mg/kg for CES1P1/CES1P1. After correction for multiple hypothesis testing, only one SNV, rs114119971, was significantly associated with weight-based dosing in two individuals. The individuals with the rs114119971 SNV had a significantly lower weight-based dose (0.42 mg/kg) as compared to those without (0.88 mg/kg; p < 0.001).

DISCUSSION

Variation in CES1 activity may impact dose requirements in children who are prescribed methylphenidate, as well as other CES1 substrates. Although intriguing, this study is limited by the retrospective nature and relatively small sample size.

HLA-associated adverse drug reactions - scoping review

Alleles of the human leukocyte antigen (HLA) system have been associated with the occurrence of idiosyncratic adverse drug reactions (ADRs). Accordingly, it is assumed that pre-emptive testing for the presence of certain HLA alleles (HLA-typing) could prevent these ADRs in carriers. In order to perceive the current evidence for HLA-associated ADRs, we conducted a scoping review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The literature search on PubMed and on Embase was carried out on the July 8 and 9, 2020, respectively. To be included in the scoping review, the studies had to investigate an association of any HLA-associated ADR with any small molecule approved and available on the Swiss market. We considered English and German primary literature published since 2002. A total of 149 studies were included, whereof most were retrospective, whereas one was a prospective randomized controlled trial. The majority of the studies (n = 33) described the association of HLA-B*15:02 with carbamazepine. It was not possible to directly compare the studies, as they were too heterogeneous in terms of the ADR definition, the HLA alleles, the number of participants, and the study types. Therefore, we summarized the results in a descriptive manner. Even if an interpretation of the outcomes remains open, the descriptive overview revealed the prevailing complexity and uncertainty in the field. For the future, consistent definitions on the different phenotypes need to be established and applied and the reporting of association studies should follow a harmonized structure.

An Update on Precision Medicine Advances In Neurodevelopmental Disorders

Neurodevelopmental disorders, including autism spectrum disorder (ASD) and attention-deficit/hyper-activity disorder (ADHD), represent a group of conditions that manifest early in child development and produce impairments across multiple domains of functioning. Although a number of pharmacological and psychosocial treatments exist to improve the symptoms associated with these syndromes, treatment advances have lagged. The Precision Medicine Initiative was launched with the goal of revolutionizing medicine by progressing beyond the historical one-size-fits-all approach. In this review, we evaluate current research efforts to personalize treatments for ASD and ADHD. Most pharmacogenetic testing has focused on the cytochrome P450 enzyme family with a particular focus on CYP2D6 and CYP2C19, which are genes that produce an enzyme that acts as a key metabolizer of many prescribed medications. This article provides an update on the state of the field of pharmacogenetics and "therapy-genetics" in the context of ASD and ADHD, and it also encourages clinicians to follow US Food and Drug Administration recommendations regarding pharmacogenetic testing.

Pharmacodynamic Gene Testing in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a rare genetic disorder with a complex neurobehavioral phenotype associated with considerable psychiatric co-morbidity. This clinical case series, for the first time, describes the distribution and frequency of polymorphisms of pharmacodynamic genes (serotonin transporter, serotonin 2A and 2C receptors, catechol-o-methyltransferase, adrenergic receptor 2A, methylene tetrahydrofolate reductase, and human leucocytic antigens) across the two major molecular classes of PWS in a cohort of 33 referred patients who met medical criteria for testing. When results were pooled across PWS genetic subtypes, genotypic and allelic frequencies did not differ from normative population data. However, when the genetic subtype of PWS was examined, there were differences observed across all genes tested that may affect response to psychotropic medication. Due to small sample size, no statistical significance was found, but results suggest that pharmacodynamic gene testing should be considered before initiating pharmacotherapy in PWS. Larger scale studies are warranted.

Clinical Practice Guideline for the Diagnosis, Evaluation, and Treatment of Attention-Deficit/Hyperactivity Disorder in Children and Adolescents

Attention-deficit/hyperactivity disorder (ADHD) is 1 of the most common neurobehavioral disorders of childhood and can profoundly affect children's academic achievement, well-being, and social interactions. The American Academy of Pediatrics first published clinical recommendations for evaluation and diagnosis of pediatric ADHD in 2000; recommendations for treatment followed in 2001. The guidelines were revised in 2011 and published with an accompanying process of care algorithm (PoCA) providing discrete and manageable steps by which clinicians could fulfill the clinical guideline's recommendations. Since the release of the 2011 guideline, the Diagnostic and Statistical Manual of Mental Disorders has been revised to the fifth edition, and new ADHD-related research has been published. These publications do not support dramatic changes to the previous recommendations. Therefore, only incremental updates have been made in this guideline revision, including the addition of a key action statement related to diagnosis and treatment of comorbid conditions in children and adolescents with ADHD. The accompanying process of care algorithm has also been updated to assist in implementing the guideline recommendations. Throughout the process of revising the guideline and algorithm, numerous systemic barriers were identified that restrict and/or hamper pediatric clinicians' ability to adopt their recommendations. Therefore, the subcommittee created a companion article (available in the Supplemental Information) on systemic barriers to the care of children and adolescents with ADHD, which identifies the major systemic-level barriers and presents recommendations to address those barriers; in this article, we support the recommendations of the clinical practice guideline and accompanying process of care algorithm.

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.