title: ADHD and poor motor performance from a family genetic perspective.
abstract: BACKGROUND
  Attention-deficit/hyperactivity disorder (ADHD) is frequently accompanied by motor problems (MPs). We investigated a possible shared etiology between the two traits in the Dutch sample of the International Multicenter ADHD Genetics study comprising 275 children with ADHD and their affected or unaffected sibling and 146 unrelated control children.
  
  
  METHODS
  Exploratory data analysis and bivariate structural equation modeling were used to estimate the familiality of MP rated by parents (Developmental Coordination Disorder Questionnaire [DCD-Q]) or teachers (Groningen Motor Observation Scale [GMO]) and to determine the familial and environmental correlation between MP and ADHD. Furthermore, the nature of the familiality was explored by studying the siblings of ADHD-affected children.
  
  
  RESULTS
  The ADHD-affected children had significantly more MP than their unaffected siblings, who in turn had significantly more MP than the control subjects. The familial component of MP measured by DCD-Q and GMO was 47% and 22%, respectively. The familial correlation between motor performance measures and ADHD was -0.38 for DCD-Q and -0.40 for GMO. Our data suggested that co-occurrence of ADHD and MP possibly marks a distinct subtype of ADHD, rather than signaling increased severity of disease.
  
  
  CONCLUSIONS
  Attention-deficit/hyperactivity disorder and MP have a common basis that may be due to genetic factors and/or shared environmental factors. Attention-deficit/hyperactivity disorder accompanied by MP may behave like a distinct subtype of ADHD, but more research will be needed to support that hypothesis.
authors.affiliation: Bavo Europoort Youth Department,Twentestraat 52, 3083 BD Rotterdam, The Netherlands. e.fliers@psy.umcn.nl
authors.forename: Ellen
authors.initials: E
authors.lastname: Fliers
authors.forename: Sita
authors.initials: S
authors.lastname: Vermeulen
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
authors.forename: Marieke
authors.initials: M
authors.lastname: Altink
authors.forename: Cathelijne
authors.initials: C
authors.lastname: Buschgens
authors.forename: Nanda
authors.initials: N
authors.lastname: Rommelse
authors.forename: Stephen
authors.initials: S
authors.lastname: Faraone
authors.forename: Joseph
authors.initials: J
authors.lastname: Sergeant
authors.forename: Jan
authors.initials: J
authors.lastname: Buitelaar
authors.forename: Barbara
authors.initials: B
authors.lastname: Franke
mesh_terms: D001072:Apraxias / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology*; D002648:Child; D006801:Humans; D011596:Psychomotor Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires