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 5% of school children, leading to hyperactivity, impulsiveness and an inability to concentrate.
Children affected by ADHD often underachieve and find it hard to interact socially.
Although there are suspected genetic links to ADHD, the mechanisms underlying the disorder remain largely unknown.
The research identifies a gene called GIT1 as an important player in ADHD.
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.
Scientists first sifted through DNA in parts of the genetic code already associated with ADHD, searching for specific genes coding for proteins that affect the function of brain neurons.
One of the strongest candidates turned out to be GIT1.
The researchers then targeted the gene in a study of 388 Korean children, 192 of whom had ADHD, looking for defective versions.
They hit on one single-letter alteration in the paired chemical elements of the genetic code, called a single nucleotide polymorphism (SNP), that was strongly linked to the disorder.
Attention deficit hyperactivity disorder (ADHD) is a group of behavioural symptoms that include inattentiveness, hyperactivity and impulsiveness, according to the NHS. ADHD is the most common behavioural disorder in the UK. It is estimated that the condition affects 3–9% of school-aged children and young people in the UK. There is no cure for ADHD but it can be managed through medication.