University of Otago department of biochemistry researcher Dr Louise Bicknell said patients with the disorder had wide variations of intellectual disability, ranging from mild to much more severe, whereby they had a poorer quality of life.
Some had other neurological features such as seizures, poor muscle co-ordination, or autism or attention deficit hyperactivity disorder (ADHD).
The mutation was first discovered in a New Zealand patient and had now been identified in 29 people in 10 countries.
DNA was wound up like thread on a spool and, until recently, the spool was often ignored and seen as just packaging material for DNA, Dr Bicknell said.
"Our genetic studies have discovered that altering this spool can disrupt brain development and functioning.
"We have found that mutations in one of the spool’s components [histone H4] causes intellectual disability and delayed development in a group of individuals from 10 different countries."
The finding would not only supply answers and reassurance to patients and their families, it would also give greater insight into the factors required for brain function.
"The family would have been told that their child’s condition is highly likely to have a genetic cause, but now through our research they will have a formal diagnosis, which can help initiate more support for the family.
"This also means that they can get information about the chances of having another child that is affected — which is very low — which helps with family planning.
"In addition to giving them an answer as to the cause of the condition, because of the large number of people we have studied, we can provide information to help with managing the disorder, and what might happen in the future.
"For example, we have several adults affected with the disorder, so this means we are able to give that information to families with young children, that you can expect your child to survive to adulthood."
Dr Bicknell said the research project would continue.
