Irish scientists have made a discovery that could lead to a better understanding of ADHD.

ADHD (attention deficit hyperactivity disorder) is a behavioural disorder, the main symptoms of which include inattention, impulsivity and hyperactivity. Those affected show poor concentration, are often unable to complete tasks, day dream a lot, are distracted easily, act without thinking and can suffer temper tantrums. Up to one in every 20 children is affected.

Now, scientists at Trinity College Dublin (TCD) have found that a mutation in a single gene, which has a role to play in the brain's nervous system, can lead to symptoms of hyperactivity that are characteristic of ADHD.

Hyperactive symptoms can include restlessness and not being able to remain seated, such as during meals. In adults, this can manifest itself through excessive talking and feelings of being overwhelmed.

According to the scientists, the brain contains billions of different types of nerve cells, which must be connected in a very specific way. This occurs as an embryo grows and it involves the actions of thousands of different genes.

The TCD team discovered that a mutation in a single mouse gene, known as Elfn 1, can have a major effect.

"Their new findings give impetus to discover whether mutations in Elfn1 in humans can give rise to similar symptoms and whether they might play a part in some patients with epilepsy and ADHD. These two conditions occur together far more often than expected by chance," the college said.

The scientists investigated the importance of Elfn1 by removing it from some mice and comparing the effects against the effects in mice with the normal gene.

While the overall anatomy of the brain remained normal, brain function was disturbed in some of those without Elfn 1. Seizures occurred in some and these became more common as time went on.

Furthermore, the scientists observed hyperactivity and this showed an unusual response to the stimulant, amphetamine. This stimulant causes hyperactivity in animals and humans with Elfn 1 present. However here, it reduced the hyperactivity of the mice without the gene.

"These findings clearly show that removal of the Elfn1 gene affects brain circuits with multiple consequences for behaviour," explained one of the investigators, Dr Jackie Dolan.

The scientists emphasised that they are ‘at the beginning of the process of figuring out how this gene works and understanding the consequences when it is mutated'.

"But, these animals provide a unique model to investigate how subtle changes in brain development can ultimately result in aberrant brain function," commented Prof Kevin Mitchell.

Prof Mitchell, Dr Dolan and a team of colleagues first discovered Elfn 1 in 2007. Their latest findings are published in the international journal, PLOS ONE.