title: The impact of individual and methodological factors in the variability of response to methylphenidate in ADHD pharmacogenetic studies from four different continents.
abstract: 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.
authors.affiliation: ADHD Program, Child and Adolescent Psychiatric Division, Hospital de Clinicas de Porto Alegre, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Guilherme
authors.initials: G
authors.lastname: Polanczyk
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Faraone
authors.forename: Claiton H D
authors.initials: CH
authors.lastname: Bau
authors.forename: Marcelo M
authors.initials: MM
authors.lastname: Victor
authors.forename: Katja
authors.initials: K
authors.lastname: Becker
authors.forename: Reta
authors.initials: R
authors.lastname: Pelz
authors.forename: Jan K
authors.initials: JK
authors.lastname: Buitelaar
authors.forename: Barbara
authors.initials: B
authors.lastname: Franke
authors.forename: Sandra
authors.initials: S
authors.lastname: Kooij
authors.forename: Emma
authors.initials: E
authors.lastname: van der Meulen
authors.forename: Keun-Ah
authors.initials: KA
authors.lastname: Cheon
authors.forename: Eric
authors.initials: E
authors.lastname: Mick
authors.forename: Diane
authors.initials: D
authors.lastname: Purper-Ouakil
authors.forename: Philip
authors.initials: P
authors.lastname: Gorwood
authors.forename: Mark A
authors.initials: MA
authors.lastname: Stein
authors.forename: Edwin H
authors.initials: EH
authors.lastname: Cook
authors.forename: Luis Augusto
authors.initials: LA
authors.lastname: Rohde
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000188:drug therapy / Q000453:epidemiology / Q000235:genetics; D000697:Central Nervous System Stimulants / Q000494:pharmacology / Q000627:therapeutic use*; D002648:Child; D015897:Comorbidity; D003710:Demography; D005260:Female; D006801:Humans; D008297:Male; D008774:Methylphenidate / Q000494:pharmacology / Q000627:therapeutic use*; D008875:Middle Aged; D015999:Multivariate Analysis; D010597:Pharmacogenetics / Q000379:methods*; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D012107:Research Design; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D008774:Methylphenidate