For years a debate has been going on about the cause of attention deficit hyperactivity disorder (ADHD). The social scientists have been arguing that it was all about nurture while the real scientists, noting the tendency for the disorder to run in families argued for a genetic cause. An important new study comes down heavily on the side of biology. (1)
One in 50 children are affected by the disorder, which attracts disapproving looks and frequent scolding from people convinced that the bad behavior is due to poor parenting, too much sugar or too many additives in the child’s diet.
Children with ADHD are impulsive and have an inability to focus, which causes difficulties at home and school, placing immense strain on their families. The burden has been aggravated by the stigma attached to the disorder which attributes responsibility to the parents.
Now scientists from Cardiff University in the UK, say the origin of the behavior is in the genes. They compared the DNA of two groups of children with and without ADHD and have discovered differences between them which provide the first direct evidence of a genetic cause.
In an interview with the BBC, Anita Thapar, professor of child and adolescent psychiatry at Cardiff University, said: “We are really excited by these findings. We have known ADHD runs in families but this is the first evidence of a direct genetic link. We hope these findings will help overcome the stigma associated with ADHD.
“Too often people dismiss it as being down to bad parenting or poor diet. As a clinician it was clear to me 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 the brains of other children.”
ADHD is known to run in families – identical twins have a three-in-four chance of having the condition if their twin also has it. But, until now, debate has raged over whether the “heritability” of the condition was the result of a shared environment or shared genes.
The researchers analyzed the genomes of 366 children who had been diagnosed by doctors with ADHD and compared them with the genomes of 1,000 controls. They found that chunks of DNA which were either missing or duplicated were twice as common in the children with ADHD. The findings are published in The Lancet.
Professor Thapar said the parts of the genome affected were the same as those involved in autism and schizophrenia, suggesting a potential overlap between the conditions.
“It gives us a window into the biology of the brain. The findings will help unravel the biological basis of the condition and could help develop treatments.”
Treatment for ADHD is limited to alleviating the symptoms with drugs, behavioral management and school support. “It is palliative. It doesn’t cure but it takes the edge off the symptoms. The hope is that by better understanding the biology we can have more specific types of medication,” Professor Thapar said.
She added that there was no evidence that bad parenting or poor diet caused ADHD, although it could affect behavior in other children. “We have looked – but we have found none. To manage children with ADHD you need to be a super-parent to handle the difficulties. But that doesn’t mean the parenting caused the difficulties,” she said.
- Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis
Dr Nigel M Williams PhD,Irina Zaharieva BSc,Andrew Martin BSc,Kate Langley PhD,Kiran Mantripragada PhD,Ragnheidur Fossdal PhD,Hreinn Stefansson PhD,Kari Stefansson MD,Pall Magnusson MD,Olafur O Gudmundsson MD,Omar Gustafsson PhD,Prof Peter Holmans PhD,Prof Michael J Owen MD,Prof Michael O’Donovan MD,Prof Anita Thapar MD
The Lancet – 30 September 2010