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The relationship between ADHD and key cognitive phenotypes is not mediated by shared familial effects with IQ
A C Wood1, F Rijsdijk, K A Johnson
1MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK. lekki.wood@googlemail.com
Psychological Medicine
|June 5, 2010
Summary
Genetic factors influencing attention deficit hyperactivity disorder (ADHD) and cognitive performance appear distinct from those affecting IQ. This suggests lower IQ doesn't explain core ADHD cognitive deficits, impacting genetic research.
Area of Science:
- Neuroscience
- Behavioral Genetics
- Psychiatry
Background:
- Attention deficit hyperactivity disorder (ADHD) is linked to specific cognitive deficits and lower IQ scores.
- Previous studies suggest cognitive phenotypes may mediate the relationship between genetics and ADHD symptoms.
- The role of shared familial influences between IQ and cognitive performance in ADHD requires further investigation.
Purpose of the Study:
- To examine whether familial factors associated with cognitive performance and ADHD are mediated by shared familial influences with IQ.
- To differentiate the etiological factors underlying cognitive impairments in ADHD from those related to IQ.
Main Methods:
- Utilized multivariate familial models on data from 1265 individuals (ages 6-18), including ADHD sibling pairs and controls.
- Assessed cognitive functions using reaction time (RT) tasks, go/no-go, choice-delay tasks, and IQ tests.
- Focused analyses on mean RT (MRT), RT variability (RTV), commission errors (CE), omission errors (OE), and choice impulsivity (CI).
Main Results:
- Confirmed significant familial associations between cognitive performance and both ADHD (rF=0.41-0.71) and IQ (rF=-0.25 to -0.49).
- The link between ADHD and cognitive performance was largely independent (80-87%) of etiological factors shared with IQ.
- Choice impulsivity (CI) showed a partial overlap (49%) with familial variance underlying IQ.
Conclusions:
- Etiological factors for lower IQ in ADHD are distinct from those linking ADHD to RT/error measures.
- Lower IQ does not appear to account for the primary cognitive impairments observed in ADHD.
- Findings have implications for molecular genetic studies seeking to identify ADHD-related genes.
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