South Korea has discovered the genetic cause of attention deficit hyperactivity disorder, or ADHD, for the first time in the world.

The Korea Advanced Institute of Science and Technology (KAIST) in Daejeon says a team led by bioscience professors Kim Eun-jun and Gang Chang-won discovered that ADHD occurs due to a lack of the protein GIT1 in the brain.

The team compared the genes of children with ADHD symptoms and ordinary children. It found that the frequency of developing ADHD was much higher in children who produced less of the protein.

Professor Kim says a deficiency of GIT1 is believed to affect the calming effect of nerve cells, which is responsible for the failure to adequately suppress excessive behavior.

The study was published in Monday’s online issue of Nature Medicine magazine.