Study is First to Find Direct Evidence That ADHD is a Genetic Disorder

In a study published online first and appearing in an upcoming edition of The Lancet, researchers have provided the first direct evidence that attention-deficit/hyperactivity disorder (ADHD) is a genetic condition.

ADHD is a brain development disorder, concluded the authors from the MRC Centre in Neuropsychiatric Genetics and Genomics, and Department of Psychological Medicine and Neurology, Cardiff University, Cardiff, United Kingdom.

For many years, ADHD has been attributed to bad parenting or high-sugar diets, despite a number of factors suggesting genetic factors are at play. For example, the child of a parent with ADHD is more likely to have the condition than a child of a parent without it. And if 1 of a set of identical twins has ADHD, the other twin has a 75% chance of having it.

The study involved genetic analysis of DNA from 366 children with ADHD and 1,047 without the condition.

The researchers found that children with ADHD were more likely to have small DNA segments duplicated or missing than controls. This type of genetic variation is found to be more common in brain disorders. Thus this new study provides the first direct evidence that ADHD is a neurodevelopmental disorder.

Furthermore, they also found significant overlap between these segments, or copy number variations (CNVs), and those linked to autism and schizophrenia. Whilst these disorders are currently thought to be entirely separate, there is some overlap between ADHD and autism in terms of symptoms and learning difficulties. This new research suggests there may be a shared biological basis to the 2 conditions.

The most significant overlap was found at a particular region on chromosome 16 which has been previously implicated in schizophrenia and other major psychiatric disorders and spans a number of genes including one known to play a role in the development of the brain.

“We hope that these findings will help overcome the stigma associated with ADHD,” said lead investigator Anita Thapar, MD, Cardiff University. “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.”
“Children with ADHD have a significantly higher rate of missing or duplicated DNA segments compared with other children and we have seen a clear genetic link between these segments and other brain disorders,” said author Nigel Williams, MD, Cardiff University. “These findings give us tantalising clues to the changes that can lead to ADHD.”

Is ADHD a genetic disorder? Having an ancestor with a particular mental illness does not necessarily imply that a family member with the same mental illness has inherited the disease. We often have to distinguish a causal relationship from a correlation, or even environmental factors. A family history of ADHD does put someone at a higher risk, yet these familial relationships are not always strictly implied, especially with our new findings of the possible etiologies of these illnesses.