A tiny genetic fault has been discovered that almost triples the chances of a child being hyperactive.
The single-letter change in the genetic code is linked to a multi-function brain protein that helps to balance excitability and inhibition.
Children with the defective gene are 2.7 times more at risk of Attention Deficit Hyperactivity Disorder (ADHD).
The behavioural condition affects around 5pc of schoolchildren, leading to hyperactivity, impulsiveness and an inability to concentrate or complete tasks.
Children affected by ADHD often underachieve and find it hard to interact socially with their classmates or adults.
Although there are suspected genetic links to ADHD, the mechanisms underlying the disorder remain largely unknown.
The new research identifies a gene called GIT1 (G protein-coupled receptor kinase-interacting protein -- 1) as an important player in ADHD.
In the study, mice whose GIT1 gene was "knocked out" and inactive suffered a range of ADHD-like traits.
Understanding how genes such as GIT1 influence ADHD could lead to the development of new drug treatments or other kinds of therapy for the disorder.
A paper on the research, led by Dr Eunjin Kim, from the Korea Advanced Institute of Science and Technology in Daejeon, South Korea, was published online in the journal 'Nature Medicine'.