title: Twin study on heritability of activity, attention, and impulsivity as assessed by objective measures.
abstract: OBJECTIVE
  The purpose of this study was to assess heritability of activity, attention, and impulsivity by comparing young monozygotic (MZ) twins with dizygotic (DZ) twins using objective measures.
  
  
  METHODS
  The OPTAx test is an infrared motion analysis to record the movement pattern during a continuous performance test. Seventeen MZ and 12 same sexed DZ twin pairs in the range of 6 to 12 years were tested. The zygosity was determined by DNA-fingerprinting. The measures under investigation were activity (microevents and spatial scaling), impulsivity (errors of commission), and attention (accuracy and variability). For statistical analyses, the classical model of Falconer and the ACE and ADE genetic model for twin data were applied in order to estimate the proportion of the variance in activity, impulsivity and attention that is due to genetic effects.
  
  
  RESULTS
  The respective coefficients of intraclass correlations in MZ twins ranged between .35 and .65 whereas for DZ twins the correlations were between .12 and .88. The heritability estimates resulting from both models were about 30% for 4 of the 5 measures, but none of these was significantly different from 0.
  
  
  CONCLUSIONS
  We found no significant influence of genetic factors for activity, attention, and impulsivity. The authors conclude that further investigation of heritability of ADHD is necessary using larger sample sizes and objective measures.
authors.affiliation: Department of Child and Adolescent Psychiatry, Philipps-University of Marburg, Germany. heiser@mailer.uni-marburg.de
authors.forename: Philip
authors.initials: P
authors.lastname: Heiser
authors.forename: Monika
authors.initials: M
authors.lastname: Heinzel-Gutenbrunner
authors.forename: Joachim
authors.initials: J
authors.lastname: Frey
authors.forename: Judith
authors.initials: J
authors.lastname: Smidt
authors.forename: Justyna
authors.initials: J
authors.lastname: Grabarkiewicz
authors.forename: Susann
authors.initials: S
authors.lastname: Friedel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kühnau
authors.forename: Jörg
authors.initials: J
authors.lastname: Schmidtke
authors.forename: Helmut
authors.initials: H
authors.lastname: Remschmidt
authors.forename: Johannes
authors.initials: J
authors.lastname: Hebebrand
mesh_terms: D001288:Attention; D001289:Attention Deficit Disorder with Hyperactivity / Q000235:genetics; D002648:Child; D004200:Diseases in Twins / Q000235:genetics / Q000523:psychology*; D007174:Disruptive, Impulse Control, and Conduct Disorders / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D012923:Social Class; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic