The study found that a neurobiological marker appears in children who have been diagnosed with ADHD. These children have more deleted or duplicated regions in their chromosomes, known as copy-number variants (CNVs), than children without the disorder. While ADHD has previously shown to be an extremely heritable psychiatric condition [see: A pair of genes to suit every occasion?] direct evidence that it can be passed down from parents to their children and not just through environmental factors counts as a major finding. The authors of the study declare that they hope this ensures that ADHD will not be seen as a purely social construct. To understand just how conclusive these findings are we need to be familiar with what is known about CNVs.

The human genome project discovered that DNA copy-number variation is much more common in humans than previously imagined. 255 areas across our DNA have been identified where these mutations can occur and 24 variants are present in 10% of individuals. The variations are of two kinds: chromosomal duplications, where extra copies of a region in a chromosome are created, and chromosomal deletions, where areas of a chromosome are not present. Both of these mutations affect how many copies of a gene are in a cell, which in turn can change how these genes function. Ultimately, these mutations can affect the development and disease susceptibility of an individual. For example, identical twins who share the same genetic material can have different CNVs, which means one twin can have a biological abnormality while the other does not. Their genes might be the same, but different copy-number variations cause them to work differently.

The study found that one in seven children with ADHD have a large number of CNVs. In children without ADHD, one in fourteen have similar CNV counts. This does not mean that having a large number of CNVs is the only cause of ADHD. Fully 85 percent of children with ADHD did not have this genomic variation. However, for those that were diagnosed with the condition, they were twice as likely to have CNVs as children without.

The study points out that similar kinds of CNV’s have been reported to increase the risk of schizophrenia and autism. The researchers conclude that all of this data shows there is a link between ADHD and these psychiatric disorders that have previously been thought to be separate.

This study is part of a long line of research that followed the completion of the human genome project a decade ago. The hope was that the project would quickly open up a whole new world of cures for various genetic ailments. But while researchers have found genes that are responsible for different illnesses, cures for everything from obesity to Alzheimer’s disease are still just aspirations and not reality. The biological complexity of the human genome has so far made these cures elusive. The discovery of a specific gene and what it does is not the same as figuring out what therapy can actually cure the disease or disorder.

The complexity is even more apparent when we look at behavioral disorders. While neuroscience has helped us understand the functioning of the human brain, we still do not know how our behaviors emerge from our genes. The variables involved in separating nature from nurture are just too immense. The whole still appears to be greater than the sum of its parts. Can genes really explain the existence of ADHD and a host of other behavioral conditions? And furthermore, can genes help us find solutions to these problems? So far genetics can only help us understand a tiny fraction about conditions like ADHD. The promise of “personalized medication” that would be tailored to suit an individual’s genetic make-up has not materialized and the medication prescribed for psychiatric disorders such as ADHD, autism, manic depression, and bipolar disorder remains crude. A growing number of children have been prescribed powerful anti-depressants, for instance, which have serious short-term side effects and no one knows their long-term effects. [see: Are we subjecting our troubled children to uncontrolled medical experiment?] .

Prevention Action believes there are dangers inherent in this latest study. Its conclusions could lead parents and providers to exclusively rely on medical treatments for ADHD, and discount environmental and behavioral interventions that could help reduce symptoms of the disorder. [see: Welsh ADHD study uncovers a two-way stretch]. The roots of the problem may be genetic, but treating ADHD needs to be comprehensive and not just a trip to the prescription pad.

While the Williams & Colleagues’ study supports the genetic origin of the condition, the vast majority of children diagnosed with ADHD have no abnormal CNV’s. The research does not provide a clear-cut explanation for what causes ADHD. Until it does, the condition will still be defined and diagnosed through behavioral signs. The true value of the study is that it legitimizes ADHD as a diagnosis and hopefully this will reduce any stigma attached to the condition. By adding to the evidence base of the biological basis for the condition, the study will make it harder to dismiss ADHD as simply the latest disorder du jour or just a result of poor diet or parenting.

References:

Williams N.M., Saharieva I., Martin A., Langley K., Mantripragada K., Fossdal R., Stefansson H., Stefansson K., Magnusson P., Gudmundsson O.O, Gustaffson O., Holmans P., Owen M.J., O’Donovan M. & Thapar A. (2010) Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: A genome-wide analysis. Lancet,, (in press)

Kalscheuer V.M., FitzPatrick D. & Tommerup N., et al. (2007), Mutations in autism susceptibility candidate 2 (AUTS2) in patients with mental retardation, Human Genetics 121, pp. 501–509.

Timimi S. & Taylor E. (2004), ADHD is best understood as a cultural construct, British Journal of Psychiatry 184, pp. 8–9.