ADHD in Children
Visual Abstract
Co-occurrence of ADHD and low IQ has genetic origins
J Kuntsi , T C Eley, A Taylor, C Hughes, P Asherson, A Caspi, T E Moffitt
Summarized by:
April 23, 2023
study source
Am J Md Genet B Neuropsychiatr Genet
Jan 2004
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What they studied
Researchers wanted to see whether there was a genetic link between IQ and ADHD and young children using a twin study.
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What they found
They found that ADHD was linked with a slightly lower IQ. This link is driven mostly by shared genetics.
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What this means
These results suggest that some genes for ADHD symptoms may also cause differences in IQ test performance.
Co-occurrence of ADHD and low IQ has genetic origins
Objectives
The relationship between ADHD and IQ is complex. Previous studies have shown that ADHD can affect individuals with all levels of IQ.
However, on average, those with ADHD tend to underperform on IQ tests.
This study wanted to examine the genetics of ADHD and IQ using a twin study.
Twin studies allow scientists to estimate the contribution of genetics towards a certain attribute. Most of our features and traits result from a combination of genetics and environment, particularly regarding the mind.
Study Quote
Previous studies show that the symptoms of attention deficit hyperactivity disorder (ADHD) and lower intelligence quotient (IQ) covary in children.
Methods
This study analyzed data from a large cohort in the United Kingdom, comprising over 1000 families with twins. When the participants were around five, researchers measured their IQ with an IQ test and asked parents and teachers about ADHD symptoms.
Study Quote
We investigated the aetiology of this association in a large population-based sample of 5-year-old twins. The twins were individually assessed on an IQ test, and data on ADHD symptoms were obtained from mother interviews and teacher ratings.
Results
Researchers found a correlation between ADHD symptoms and IQ. Those with stronger ADHD symptoms were likelier to have slightly lower IQ scores. Overall, ADHD was linked with a nine-point reduction in IQ scores. However, this was a weak correlation. Like previous studies, there were children of all levels of IQ with ADHD.
Most of this relationship was driven by genetics. The same genes behind ADHD symptoms also likely caused lower IQ scores.
Researchers found that 40% of the variation in IQ could be attributed to the child’s genetics, while 31% could be attributed to the environment that a child shares with their siblings.
For ADHD, the majority of the variation in symptoms was caused by genetics. The results of this study suggest that your genes play an enormous role in determining your risk of developing ADHD symptoms as a child.
Study Quote
Confirming previous studies, the phenotypic correlation between ADHD symptom scores and IQ was -0.3 and, in a categorical analysis, children with a Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) ADHD research diagnosis obtained IQ scores nine points lower, on average, tha...
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Conclusions
Based on the study, researchers concluded that any of the genes for ADHD could potentially also contribute to IQ scores.
Study Quote
Some candidate genes for ADHD could also contribute to variation in IQ or vice versa.
However, it is important to note that there are many explanations for these data. The results do not prove that ADHD reduces IQ.
IQ tests require a certain amount of focus and attention, which can be difficult for children with ADHD. Previous studies have shown evidence that grades and test scores in those with ADHD are often lower because of ADHD symptoms themselves.