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ADHD and Genetics

by Steven Novella, Oct 04 2010

A new study published in the Lancet purports to show a potential genetic link to ADHD (Attention Deficit Hyperactivity Disorder). While the genetic link found in this study has been somewhat overhyped in the media, the results are interesting.

The main problem with media reporting is that they tend to oversimplify the concept of a genetic disorder. The worst offenders speak of “the gene” for whatever is being discussed, like ADHD. There are purely genetic disorders that are the result of a mutation in a single gene, but more often diseases and disorders that have a genetic component are the complex result of multiple genes and their interaction with the environment. Therefore there is no single gene for ADHD, autism, migraines, obesity or other complex condition.

Saying that there is a “genetic link” to a disorder is more reasonable, but always must be put into context. What this study shows is an increased risk of copy number variants (CNVs) in people with a confirmed diagnosis of ADHD. A CNV is either a deletion or duplication of genetic material. The researchers found that 78 out of 1047 control had such CNVs (7%), while 57 out of 366 subjects with ADHD did (15%). This was a statistically significant increase. Further, CNV were more likely to occur on genes previous associated with both autism and schizophrenia (and therefore likely to be involved in brain development).

The authors conclude:

“Our findings provide genetic evidence of an increased rate of large CNVs in individuals with ADHD and suggest that ADHD is not purely a social construct.”

That conclusion needs to be parsed very carefully – they are saying that this study is evidence that ADHD is not purely social. They are not saying that it is purely or even mostly genetic. In fact, only 15% of subjects with ADHD demonstrated increased CNVs. This study is a proof of concept more than anything, demonstrating that genetic makeup can contribute, at least in some cases, to the clinical syndrome of ADHD.

This makes sense in light of our understanding of similar neurological disorders. Many such disorders are defined clinical by a collection signs and symptoms, which in turn relate to some particular function or functions of the brain. However, there is likely to be many underlying causes (from a neuro-anatomical point of view) of such altered function. In other words, there may be many underlying alterations of brain function that lead to the final common pathway that results in the recognized signs and symptoms. Many neurological syndromes are defined by that final common pathway, not the underlying disorder that lead to it.

And so complex syndromes like ADHD, autism, and schizophrenia are likely many underlying disorders all with a similar clinical manifestation that we recognize and name. It is helpful to understand what the nature of the clinical manifestation is, specifically with respect to whether it is mostly a construct of environment or an effect of brain development and hard-wiring.

This study supports the plausibility that ADHD can be a problem of brain development, genetically determined. The fact that only 15% of subjects showed the genetic changes the researchers were looking for does not mean that the other 85% have no genetic link – they could have other genetic changes that this study was not designed to detect.

Previous studies have also shown genetic alterations in some subjects with ADHD (for example). Researchers are also beginning to identify genetic subtypes that may respond better to certain medications.

We are still a long way from understanding the relevant genetics, but it is reasonable to say that genetic research into ADHD has been fruitful and is likely to continue to bear fruit. But the picture that is emerging (as with many other disorders) is that of a complex relationship among many genes and interaction with the environment. This makes it complex to talk about what “causes” ADHD (which itself is likely not a single discrete entity). This further means that accurately reporting about ADHD research requires some nuance and care – something which seems to be on the wane in science journalism.

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10 Responses to “ADHD and Genetics”

  1. Jennifer says:

    I’ve been reading what Brain Balance – http://www.brainbalancecenters.com – has to say about the issue: that all neurobehavioral disorders have in common an underlying condition called functional disconnection syndrome. Through diet, behavior modification, brain exercises and educational techniques that help make connections, you can reduce or even eliminate symptoms. While their site doesn’t really talk cause (environment, genetics, etc.) it is worth a read, particularly the “truth” section. I think it gets to the heart of what you can DO once your loved one is affected. They are brain based, not drug based… it’s a much more natural approach to improving brain function.

  2. What is everyone’s opinion on the idea that a certain percentage of folks with ADHD might have been adaptive to our early clusters of hominid ancestors? I know it’s evolutionary psychology, and thus a bit . . . speculative, but it has that pleasing “passes the gut check” quality that we should all be wary of.

    ~Rhaco

    • MadScientist says:

      In the absence of evidence from carefully crafted experiments or population studies, in a scientific environment such ideas are rapidly dismissed as pure speculation. That doesn’t mean that people believe it’s wrong, only that there is not enough evidence to convince them that it’s right.

  3. CW says:

    In a book I read recently “Evolution RX” the author, Dr. William Meller, described hypothetical scenarios where ADHD would have been a survival advantage. While there’s no evidence for this, the way it was described did seem like a plausible hypothesis.

  4. Mario says:

    Interesting, I specially like enough remarks about all the media hype about genetic findings of any kind, since many people are very found of reading just headlines and they are only useful at spreading misleading information (even among people with high education level).

    It constitutes another piece on that huge puzzle that are the neurological disorders most of them are more related than we can see now since they’re produced in an early embryonic state, we are getting closer every day to solve it.

  5. bruce says:

    “this study is a proof of concept more than anything, demonstrating that genetic makeup can contribute, at least in some cases, to the clinical syndrome of ADHD.”

    How does 15% vs 7% prove anything? What is your level of proof? What kind of skepticism is this? How many times have the headlines read “Gene for schizophrenia found”? How many times has the press been duped by geneticists notoriety and more grant money?

  6. John Greg says:

    Novella says:

    That conclusion needs to be parsed very carefully – they are saying that this study is evidence that ADHD is not purely social. They are not saying that it is purely or even mostly genetic. In fact, only 15% of subjects with ADHD demonstrated increased CNVs. This study is a proof of concept more than anything, demonstrating that genetic makeup can contribute, at least in some cases, to the clinical syndrome of ADHD.

    I’m a bit confused by that paragraph. Does that mean that ADHD (ADD) is currently considered purely (or mostly? Somewhat?) a social construct (and/or an invention of the pharmaceutical companies)? Or is ADHA (and ADD) currently considered a real, or legitimate disorder/disease?

    I ask because 13 or 14 years ago I was writing a research paper on the sociology of medicine in Canada, and in my researches I came across a handful of Candian research papers that had been published by the APA and in a couple of respected medical journals that argued that ADHD and ADD were examples of the medicalization (is that the correct word? I’ve forgotten….) of a common, non-disorder, non-disease behavioural phenomenon, “invented” by the applicable pharmaceutical companies as a way of finding an effective additional target for ritalin and increasing sales. Is that research now considered false? I’m sorry I can provide no links. As I say, it was many years ago and the research papers were read on paper, in a library, and not online, and I cannot remember at this long remove who they were by.

    And please, all you hearty defenders of so-called Big Pharma, please don’t get all up in arms. I am making no claims nor pointing any fingers here. I’m only asking questions.

    • Max says:

      The study’s conclusion does challenge the idea that ADHD is purely a social construct:
      “Our findings… suggest that ADHD is not purely a social construct.”

      So the question is what they mean by a social construct. You assume it means making up a fake disease, but Steve compared ADHD to schizophrenia: “And so complex syndromes like ADHD, autism, and schizophrenia are likely many underlying disorders all with a similar clinical manifestation that we recognize and name.”

  7. Gregory Goldmacher says:

    Genetics and neurology is a classic situation of high “causal density” – many different causes, contributing variously to many different effects. Of course it’s tempting to try to boil things down to simple one-to-one correspondences.

    On that subject, here’s a fascinating article from a while back about the genetic impact of the maternal and paternal genes on the development of disease in autism spectrum disorders and schizophrenia.

    http://www.edge.org/3rd_culture/badcock08/badcock08_index.html

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