New research suggests that attention deficit/hyperactivity disorder (ADHD) may have a genetic basis.
Researchers found that children diagnosed with ADHD were more likely to have duplicate or missing segments in their DNA than children without the diagnosis.
The study was led by Anita Thapar and a team of researchers based at the MRC Centre for Neuropsychiatric Genetic and Genomics at Cardiff University.
The new research included an analysis of 366 children clinically diagnosed with ADHD. A comparison was made of the genomes of these children against the genomes of more than 1,000 control samples.
Specifically, researchers were in search of variations in genetic makeup that were more common in children with ADHD.
“We hope that these findings will help overcome the stigma associated with ADHD,” said Thapar, a professor of child and adolescent psychiatry at the university.
“Too often, people dismiss ADHD as being solely down to bad parenting or poor diet. Now we can say there is this class of genetic contribution to ADHD and that there are genetic similarities with autism and schizophrenia. There will be other types of genetic variation that also contribute as well as of course environmental influences.”
The study also found significant overlap between these DNA segments, known as copy number variants (CNVs), and genetic variants implicated in other neurodevelopmental disorders such as autism and schizophrenia.
Researchers pointed out that this similarity does not mean that these conditions are the same but does provide evidence that ADHD is a neurodevelopmental disorder. Rare CNVs were almost twice as common in children with ADHD compared to the control group – and even higher for children with learning difficulties.
“These valuable findings show how genes may play a role in conditions such as ADHD. The exact causes of ADHD are not yet known, but it’s clear that both genetic and environmental factors like diet and social circumstances are part of the puzzle. More research is needed to determine just how much influence genes have over other factors and we look forward to what future studies show,” said Chris Kennard, professor and chair of the MRC Neuroscience and Mental Health Board.
ADHD is one of the most common mental health disorders in childhood, affecting around one in 50 children in the UK. Children with ADHD are excessively restless, impulsive and distractible, and experience difficulties at home and in school. Although no cure exists for the condition, symptoms can be reduced by a combination of medication and behavioral therapy.
The condition is considered highly heritable in that children with ADHD are statistically more likely to also have a parent with the condition. A child with an identical twin with ADHD has a 75 percent chance of also having the condition.
The paper was published in The Lancet on September 30, 2010.
Source: Medical Research Council