ADHD is the most common behavioural problem in Britain and is estimated to affect 3%-9% of schoolchildren. This is no single, well-defined disorder, but rather a group of symptoms that include impulsivity, difficulty concentrating, restlessness and fidgeting.
The impact can be serious. The child might not be able to feed him or herself, may struggle to make and keep friends, and is at risk of underachieving. Since most perfectly healthy children are prone to these kinds of behaviours, diagnosing ADHD is not straightforward.
The trouble began with a study in the Lancet medical journal by researchers at Cardiff University who found children with ADHD were more likely to have duplicate or missing chunks of DNA than other children. A press release from the Wellcome Trust, which partly funded the study, declared the work “the first direct evidence that attention-deficit hyperactivity disorder is a genetic condition”. Professor Anita Thapar, who led the study, hoped the findings would lay to rest the myth that ADHD was down to bad parenting and poor diet.
The row that followed was needless. The child psychologist Oliver James attacked the Cardiff group on the BBC for hyping their findings and pointed out that “only 57 of the 366 children with ADHD in the study had the genetic variant supposed to be a cause of the illness”. Most ADHD in children must be caused by something other than genes, he concluded.
Anyone hoping to learn about the disease and how it comes about must have been truly baffled. But the row was born of lazy phrasing and misunderstandings. ADHD is not caused by bad genes. Nor is it caused by a bad environment. It is a consequence of both. Calling ADHD a “genetic condition” is as unhelpful as blaming it solely on other factors, such as poor parenting or diet.
Another misunderstanding is the impression that Thapar’s team found genetic differences that cause ADHD. They found genetic variations that seem to raise the risk of ADHD. There is a crucial difference. Professor Lindsey Kent at the University of St Andrews compares it to cigarettes: smoking raises the risk of coronary disease, but not everyone who smokes has a heart attack and plenty of people who do not smoke will have.
The ultimate cause of ADHD is complex. Genes will play a role and some genetic glitches that raise the risk of ADHD may be more common than others. But there could also be large numbers of other defects that each raises the odds a tiny amount. To confound scientists even more, these genetic quirks may differ from one family to another.
And what of the environment? So far, there is no firm evidence for any environmental factors actually causing or raising the risk of ADHD. Caffeine often makes children’s symptoms worse if they already have ADHD, but it does not seem to cause the disorder. Finding out what environmental factors do contribute to ADHD – whether they include the behaviour of the mother in pregnancy, or the environment of the child – is a pressing challenge for scientists.
Unravelling the root causes of ADHD will give scientists their best hope of devising new treatments for this common and ill-defined disorder. A section of DNA that is more common in children with ADHD than others could ultimately reveal how biology goes wrong to cause impulsivity and restlessness, even if it does not give the full picture. Last week’s debacle over ADHD showed how vital it is for scientists to make their message clear.
The Guardian UK