For the first time, evidence has been found that ADHD, or attention deficit hyperactivity disorder, has a genetic basis, reports the Lancet weekly.

According to the paper’s authors, this may help to conclusively dispel the myth that ADHD is merely the result of parenting errors.

ADHD is a common developmental disorder. It is estimated to affect 3-7 per cent of school-aged children. It manifests as a child’s busyness and impulsivity, difficulty concentrating and susceptibility to distractions.

Children with ADHD cause many problems at home and school. However, this is not due to their ill will, but to their difficulty in controlling their emotions, behaviour and impulses. In fact, they themselves suffer a lot from this – they have problems at school, with their peers, are often disliked, and become the scapegoat in class. Because of their impulsivity, children with ADHD are also more likely to be involved in traffic accidents, dangerous behaviour – such as alcohol or drug abuse, unprotected sex, often drop out of school, and have conflicts with the law in adolescence and adulthood.

For many years, children with ADHD were simply treated as naughty, and their behaviour was attributed to parental errors, or less frequently to a poor diet too rich in easily digestible sugars. In fact, such myths persist in society to this day, making it difficult for children with the disorder to get support and help at school or in everyday life. Although ADHD is currently not curable, with therapy directed primarily at the parents, it is possible to help the child function better and fulfil his or her intellectual potential. A relatively small number of ADHD sufferers require pharmacotherapy.

Scientists and doctors working with children with the disorder have previously suspected that genetic factors may contribute to it. It is known, for example, that the child of a parent who has ADHD is more likely to have the disorder, and if one of the monozygotic twins (with almost identical DNA) suffers from ADHD, 75 per cent of the other will also have it.

Cardiff University researchers carried out a genetic analysis of the DNA of 366 children with ADHD aged 5-17 years and 1,047 unrelated peers without the disorder.

They found that children with ADHD were significantly more likely to have large fragments of DNA missing or duplicated, comments one of the paper’s authors Dr Nigel Williams. These changes are known as DNA fragment copy number variants (CNVs) and are more common in people with psychiatric disorders or disorders of brain development. Large, rare CNVs have been observed markedly more frequently in children with ADHD, particularly in those with intellectual disabilities.

Moreover, many of these lesions overlapped with CNVs previously associated with schizophrenia and autism. This was particularly true for CNVs on chromosome 16, which involve multiple genes, including one that plays an important role in brain development. Although all of these disorders are thought to be completely independent of each other, the latest discovery suggests that they may share a partly common biological basis.

As study co-author Dr Kate Langey explains, ADHD is not caused by a single genetic change, but rather by multiple changes – among other CNVs – that interact with as yet unidentified environmental factors. Testing children for large, rare CNVs will not help diagnose ADHD. Currently, there are already very stringent diagnostic criteria for the disorder, the researcher points out.

Instead, the authors of the paper believe that their discovery should dispel many myths about ADHD. We hope that our discovery will help to change attitudes towards ADHD. Too often people underestimate the disorder, attributing it to parenting errors or poor diet. It has always been clear to me that this is not the case. We can now confidently say that ADHD is a genetic disorder and that the brains of children who suffer from it develop differently from those of their peers, comments research leader Prof Anita Thapar.

ADHD should be seen as a disorder of brain development rather than a behavioural disorder, the researchers conclude. They hope that in the future, their discovery will help to better understand the biological basis of ADHD and lead to the development of new, more effective treatments for it.