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Is ADHD genetic? New evidence says yes.

5:37 am by | 3 Comments

Diagnoses of Attention Deficit Hyperactivity Disorder (ADHD), like those of food allergies, have risen dramatically in children over the last few generations. And again like food allergies, the cause is unclear. However, a team of researchers in England recently identified a genetic link for the disorder [1]. The study, published in The Lancet, found that children with ADHD were more likely to have small segments of their DNA duplicated or missing than other children that don’t have the disorder.

ADHD is one of the most common mental health disorders in childhood, affecting approximately 2% of children [2]. It is characterized by intense motor restlessness, problems with concentration and radical impulsivity. While it’s known that ADHD is highly heritable, there hasn’t been an identification of specific susceptibility genes until this study. Researchers compared the genomes of children with ADHD to healthy controls and found chromosomal duplications and deletions in the ADHD group.

In theory, we each have two copies of every gene: one on the chromosome from our mother and the other on the chromosome from our father. In reality, however, this isn’t necessarily the case. The Human Genome Project revealed that Copy Number Variations (CNVs) — the presence of more or less than two copies of a region of DNA due to its duplication or deletion — is quite widespread in humans. CNVs have been shown to be associated with a number of human maladies, including cancer, susceptibility or resistance to HIV infection, and notably, neurodevelopmental disorders and intellectual disabilities.

The genomes of 366 white British children (316 boys and 50 girls) with ADHD between the ages of 5 and 17 were included in the study, which took place between 2001 and 2009. Children with neurological disorders like schizophrenia, Tourette’s syndrome, autistic spectrum disorders or epilepsy were excluded from the study. These disorders are known to have higher rates of CNVs and researchers did not want to bias the study; they wanted to be sure that any extra CNVs they saw were due solely to ADHD. Control genomes came from 1,047 British men and women born during one week in 1958. The study was then repeated with an Icelandic population — 825 patients with ADHD and 35, 243 controls — to independently confirm the results.

The scientists looked for large CNVs spanning at least 500 kilobases of DNA as these are the easiest to detect accurately and are known to be associated with neurodevelopmental disorders. Children with ADHD exhibited twice as many large CNVs as controls, both deletions and duplications. The excess was most apparent in, but not limited to, children who had intellectual disabilities (IQ lower than 70) along with ADHD. There were some CNVs in the ADHD children that overlapped with regions of the genome implicated in autism spectrum disorders. Six duplications observed in patients with ADHD span a region of the genome known to be involved in schizophrenia. No duplications of this region were found in controls; however, a deletion was observed in one control individual.

This region is located on the short arm of chromosome 16 and contains seven genes. One of them — nuclear distribution gene E homologue 1 (NDE1) — is particularly interesting because it plays a role in neurodevelopment and interacts with disrupted in schizophrenia 1 (DISC1), a gene implicated in schizophrenia and other major psychiatric disorders that encodes a protein also involved in neurodevelopment. Duplications in this region have also been detected in patients with autistic spectrum disorders and intellectual disabilities. Although ADHD is currently thought to be completely separate from schizophrenia and autism, there is some overlap in terms of clinical symptoms and cognitive deficits. These recent findings suggest there is a shared biological basis to these disorders.

The researchers note that they do not intend for children to be screened for these CNVs as a means of diagnosing ADHD -– there are rigorous clinical assessments for that. Rather, they set out to demonstrate that ADHD clearly is a genetic disease and that the brains of children with ADHD are different from those without it.

Dr. Anita Thapar, Professor of Child and Adolescent Psychiatry at Cardiff University School of Medicine who led the study, said [3]:

We hope that these findings will help overcome the stigma associated with ADHD. Too often, people dismiss ADHD as being down to bad parenting or poor diet. As a clinician, it was clear to me that this was unlikely to be the case. Now we can say with confidence that ADHD is a genetic disease and that the brains of children with this condition develop differently to those of other children.

References

  1. Williams et al. Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis. Lancet. 2010 Oct 23;376(9750):1401-8. Epub 2010 Sep 29.
    View abstract
  2. Franke et al. Genome-wide association studies in ADHD. Hum Genet. 2009 Jul;126(1):13-50. Epub 2009 Apr 22.
    View abstract
  3. ADHD’s genetic link. Cardiff University News Centre. 2010 Sep 30.
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Highlight HEALTH is a new media news organization that promotes advances in biomedical research and new ideas in health and medicine.
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3 comments
D. Wilson
D. Wilson

We might try leaving kids alone and not forcing our fantasies on them. Those fantasies have led us to the state we're in today. Financial meltdown, war, world wide suffering and the destruction of natural foods, clean water and so on. Why do full grown humans insist children pay attention so they might become part of this dysfunctional societal idea? We might learn from children, they might be telling us - it's not worth their attention. We are the ones who need to pay attention - attention to the reality of our situation. Leave children alone and in their natural environment and they'll be just fine. But, first we'll need to restore a natural environment.

Benaiah Marshall
Benaiah Marshall

John- Explain to me on how you have become the leader in the diagnosis of an ADHD sufferer? Your argument is that of a biased and uninformed casual naysayer. You say that you are a formal principal and therefore, you have had access to the first hand nature of children struggling with ADHD. For you to make a blanket statement saying that it is not a disorder, just goes to show everyone what is wrong with our you and our educators. I assume that you are of the thought that if a child is not "paying attention" that a sharp word and or discipline would be the best course of action in order to "bring their attention" back. You're wrong sir. You say that attention is a "learned skill". That statement reaks more of personal opinion then a cold hard fact. I challenge you to try to explain your hypothosis to a person who can not control their impulsive mind wanderings. Try to explain that to a child that can't control the amount of daydreaming that they do. Try to explain that to the child, on a strict sugar diet regimen, who cannot control their ability to sit still. It is not so much that we CAN'T pay attention, it is that when we are paying attention, our attention my be diverted to something else that grabs it. I am extremely excited that you have put your nonsensical ramblings and inaccuracies into print to show America first hand, how uneducated an educator in our schools systems can actually be. Before you judge our children, please try to learn how to understand and care about them.

john glennon
john glennon

Labeling ADHD a 'disorder' is tragic and is probably no more a disorder than being left or right handed. We are all born with certain traits, characteristics, and other genetic endowments. How those are expressed is closely related to our environment (see epigenetic theory). We have forgotten, as a society, that attention is a learned skill. Because of our genetic endowment, the ability to attend varies with each individual; some individuals have greater capacity than others, but everyone can learn to improve attention. Everyone. If attention difficulties vastly affect one's life, perhaps it should be labeled a disorder, but that would mean that very few people would be diagnosed. That of course would prevent the pharmaceutical companies from selling vast amounts of ADHD medication -- more in the US than any other nation on the planet. As a former elementary school principal, I am quite aware that attention difficulties are just the tip of the iceberg. ADHD children can't filter out distractions, finish tasks on-time, use their memory optimally, etc. A pill doesn't teach these skills, but as an educator, I can. I found and used Play Attention (www.playattention.com) and ADHD Nanny (www.adhdnanny.com). We've been very successful with these approaches. Happy parents, better grades, and better students. It's just important to know that medicine teaches nothing. Parents and teachers must actively participate to help change a child's life.