An international DNA and brain structure study led by Queensland researchers is shedding light on the causes of attention deficit hyperactivity disorder (ADHD) and Parkinson's disease.
Around one in 20 Australians have ADHD, while Parkinson's disease affects an estimated 10 million people worldwide, with roughly 38 Australians diagnosed with the devastating and incurable progressive movement disorder every day.
Both these conditions are rising globally and have a deep and profound impact on those diagnosed.
The study, the largest of its kind, used genetic and saliva testing to identify how genetic variants influence brain structure.
Associate Professor Miguel Rentería and PhD candidate Luis García-Marín from the Queensland Institute of Medical Research (QIMR) Berghofer led 189 international researchers who analysed DNA data and MRI scans of the brain from 76,000 participants.
The findings were published in the journal Nature Genetics today.
"This is the largest and most geographically diverse genetic study of human … brain volume," Mr García-Marín said.
"Seventy-five thousand people from 19 countries underwent MRI scans and provided saliva samples for DNA genotyping so that we could identify the genetic variants … that determine the volume of specific brain structure."
Luis García-Marín from QIMR Berghofer says it is the largest study of its kind. (Supplied)
Mr García-Marín said they analysed key subcortical regions — also known as the "deep brain" — which are "crucial in our day-to-day life".
They include memory formation, emotional regulation, motor control and sensory processing.
Mr García-Marín said they observed more than 254 genetic variants that can influence key parts of the brain and carry a higher risk for both Parkinson's and ADHD.
"Some of those genetic variants are increasing or decreasing the risk of … ADHD or Parkinson’s disease," Mr García-Marín said.
"Larger brain volumes tend to increase the risk of Parkinson’s disease later in life and smaller brain volumes tend to increase the risk of ADHD."
Associate professor Miguel Renteria says more research needs to be done to firm up the links. (Supplied)
Associate professor Miguel Renteria said it offers significant insight into how to intervene.
"There is strong evidence that ADHD and Parkinson's has a biological basis, and this research is a necessary step to understand, and eventually treating these conditions more effectively," he said.
"By understanding how our genes determine our brain structure … we can better prevent, diagnose and treat these conditions better in the future," he said.
Mr García-Marín said while the findings are significant, more investigation is needed before genes can be causally linked with various diseases.
"Scientists all over the world will be able to leverage what we've generated in this study to keep conducting research … specifically genetics research for mental health disorders," he said.