title: How 'core' are motor timing difficulties in ADHD? A latent class comparison of pure and comorbid ADHD classes.
abstract: Children with attention-deficit/hyperactivity disorder (ADHD) have motor timing difficulties. This study examined whether affected motor timing accuracy and variability are specific for ADHD, or that comorbidity with autism spectrum disorders (ASD) contributes to these motor timing difficulties. An 80-trial motor timing task measuring accuracy (μ), variability (σ) and infrequent long response times (τ) in estimating a 1-s interval was administered to 283 children and adolescents (8-17 years) from both a clinic and population based sample. They were divided into four latent classes based on the SCQ and
  L data. These classes were: without behavioral problems 'Normal-class' (n = 154), with only ADHD symptoms 'ADHD-class' (n = 49), and two classes with both ASD and ADHD symptoms; ADHD(+ASD)-class (n = 39) and ASD(+ADHD)-class (n = 41). The pure ADHD-class did not deviate from the Normal class on any of the motor timing measures (mean RTs 916 and 925 ms, respectively). The comorbid ADHD(+ASD) and ASD(+ADHD) classes were significantly less accurate (more time underestimations) compared to the Normal class (mean RTs 847 and 870 ms, respectively). Variability in motor timing was reduced in the younger children in the ADHD(+ASD) class, which may reflect a tendency to rush the tedious task. Only patients with more severe behavioral symptoms show motor timing deficiencies. This cannot merely be explained by high ADHD severity with ASD playing no role, as ADHD symptom severity in the pure ADHD-class and the ASD(+ADHD) class was highly similar, with the former class showing no motor timing deficits.
authors.affiliation: Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Reinier Postlaan 12, 6525 GC, Nijmegen, The Netherlands. Jolanda.vanderMeer@radboudumc.nl.|Karakter Child and Adolescent Psychiatry University Center Nijmegen, Nijmegen, The Netherlands. Jolanda.vanderMeer@radboudumc.nl.
authors.forename: Jolanda M J
authors.initials: JM
authors.lastname: van der Meer
authors.affiliation: Department of Psychiatry, University of Groningen Medical Centre, Groningen, The Netherlands.
authors.forename: Catharina A
authors.initials: CA
authors.lastname: Hartman
authors.affiliation: Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Reinier Postlaan 12, 6525 GC, Nijmegen, The Netherlands.|Karakter Child and Adolescent Psychiatry University Center Nijmegen, Nijmegen, The Netherlands.
authors.forename: Andrieke J A M
authors.initials: AJ
authors.lastname: Thissen
authors.affiliation: Karakter Child and Adolescent Psychiatry University Center Nijmegen, Nijmegen, The Netherlands.|Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
authors.forename: Anoek M
authors.initials: AM
authors.lastname: Oerlemans
authors.affiliation: Department of Psychiatry, University of Groningen Medical Centre, Groningen, The Netherlands.|Department of Clinical Neuropsychology, VU University Amsterdam, Amsterdam, The Netherlands.
authors.forename: Marjolein
authors.initials: M
authors.lastname: Luman
authors.affiliation: Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Reinier Postlaan 12, 6525 GC, Nijmegen, The Netherlands.|Karakter Child and Adolescent Psychiatry University Center Nijmegen, Nijmegen, The Netherlands.
authors.forename: Jan K
authors.initials: JK
authors.lastname: Buitelaar
authors.affiliation: Karakter Child and Adolescent Psychiatry University Center Nijmegen, Nijmegen, The Netherlands.|Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
authors.forename: Nanda N J
authors.initials: NN
authors.lastname: Rommelse
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000453:epidemiology; D000067877:Autism Spectrum Disorder / Q000175:diagnosis* / Q000453:epidemiology; D002648:Child; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D011930:Reaction Time / Q000502:physiology*; D013647:Task Performance and Analysis
keywords: ADHD; ASD; Latent class analyses (LCA); Motor timing; Variability