Is ADHD Genetic?
Is this common belief neuroscience or neuroscience fiction?
Posted Mar 18, 2015
Is ADHD a genetic disorder? This seems to be the accepted view among American psychiatrists and parents. However, when we take a close look at the research supporting this idea, the view that ADHD is caused by genetic factors does not seem to be backed by solid scientific research.
A major study that promoted a genetic factor in ADHD was published in the prestigious medical journal The Lancet in 2010. An international research team found that children diagnosed with ADHD were more likely than other children to have a particular genetic anomaly. The study's conclusion, "ADHD is not purely a social construct," was echoed by several prominent newspapers and other news sources.
However, a research team led by Professor François Gonon at the University of Bordeaux found that this study had many flaws. Of the 366 children diagnosed with ADHD, 33 also had mental retardation. By its very definition, a diagnosis of ADHD excludes mental retardation.
Gonon's team also found that the prevalence of the genetic anomalies (alleles or variants of the DRD4 gene) in children with ADHD alone was relatively small compared to the control group: 12 percent versus 7.5 percent. This result indicated a risk factor, but certainly not a cause, since 78 percent of the kids diagnosed with ADHD did not have the allele.
Gonon pointed out that the researchers did not provide even a "hint" of a genetic test to confirm an ADHD diagnosis. The genetic anomaly does not occur in all or even in most children wih ADHD. The ADHD diagnosis is based merely on behavioral symptoms, not on a genetic analysis.
Other researchers, like child psychologist Oliver James and Professor Lindsey Kent of the University of St. Andrews in the UK, criticized the study for hyping the findings. They pointed out that the genetic variation might at most be a risk factor for ADHD, but scarcely a cause.
To put this in perspective, consider a genuine genetic-based illness such as Down Syndrome, in which 100 percent of the children diagnosed have a genetic anomaly, namely an extra copy of chromosome 21, and there is a genetic test for the disease. Behavioral symptoms are not considered in making a diagnosis.
If researchers find a genetic anomaly in 100 percent of children diagnosed with ADHD as well as a test on which to base the diagnosis, that would support the view that ADHD is a genetic-based disease. Until then, ADHD remains a subjective (some would say fictional) diagnosis based merely on behavioral symptoms.
(A note on "twin studies" that purport to prove that ADHD is coded in genes. Richard Lewontin and his co-authors, in Not in Our Genes, point out that adults tend to treat fraternal twins as different individuals. Identical twins, on the other hand, tend to spend more time together and behave in ways that are more similar than fraternal twins. Therefore, research that finds that identical twins are more likely than fraternal twins to share behaviors that are labeled as ADHD can be explained in terms of environmental differences. See also Jay Joseph's book, The Trouble with Twin Studies.
Copyright © Marilyn Wedge, Ph.D.
My new book, A Disease Called Childhood: Why ADHD Became an American Epidemic, takes a deeper look at the "science" supporting the view that ADHD is a biologically based mental disorder. I discuss the "new neuroskepticism" of researchers like François Gonon and Stanford Professor John Iaoniddes.
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