An examination of the impact of attention-deficit hyperactivity disorder on IQ: a large controlled family-based analysis.
OBJECTIVE
Although children with attention-deficit hyperactivity disorder (ADHD) have, on average, lower intelligence quotient (IQ) scores than control subjects, the reasons for these deficits remain unknown. Because IQ is highly familial, we investigated whether children with ADHD have a decrement in IQ from expectations based on parental IQ.


METHODS
Subjects were 276 children with ADHD and 239 control subjects of similar age and sex. Expected IQ was calculated based on biological parents' estimated IQ. A significant discrepancy between observed and expected estimated IQ was defined by a child scoring 15 IQ points or more lower than expected, based on parental IQ.


RESULTS
Compared with control subjects, children with ADHD were significantly more likely to have lower than expected estimated IQ scores based on parental IQ, though this finding was accounted for by a small subgroup of children with ADHD who had an IQ 15 points or more lower than expected, based on parental IQ. These children were more likely to be female, have higher psychopathological, neuropsychological, educational, and interpersonal deficits, as well as higher rates of perinatal complications.


CONCLUSIONS
Group differences in IQ scores between children with and without ADHD reported in the literature may be accounted for by a subgroup of children with ADHD who have a large decrement in IQ from expectations based on parental IQ. Although perinatal complications may explain these findings, more work is needed to better understand the etiology of these IQ deficits.
Massachusetts General Hospital, Boston, MA, USA. jbiederman@partners.org
Joseph
J
Biederman
Ronna
R
Fried
Carter
C
Petty
Laura
L
Mahoney
Stephen V
SV
Faraone
D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000150:complications* / Q000453:epidemiology / Q000523:psychology; D002648:Child; D003430:Cross-Sectional Studies; D004522:Educational Status; D056348:Emotional Intelligence; D005190:Family / Q000523:psychology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000523:psychology; D006801:Humans; D008607:Intellectual Disability / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology; D007360:Intelligence / Q000235:genetics*; D007361:Intelligence Tests / Q000706:statistics & numerical data*; D008297:Male; D008570:Memory, Short-Term; D010290:Parents / Q000523:psychology*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D012107:Research Design; D012307:Risk Factors; D012737:Sex Factors