Twin study on heritability of activity, attention, and impulsivity as assessed by objective measures.
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.
Heiser
Philip
P
Department of Child and Adolescent Psychiatry, Philipps-University of Marburg, Germany. heiser@mailer.uni-marburg.de
Heinzel-Gutenbrunner
Monika
M
Frey
Joachim
J
Smidt
Judith
J
Grabarkiewicz
Justyna
J
Friedel
Susann
S
Kühnau
Wolfgang
W
Schmidtke
Jörg
J
Remschmidt
Helmut
H
Hebebrand
Johannes
J
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