Weighing in: Brain volume in specific regions may increase the risk of neurological and neurodevelopmental conditions
Spanning nearly 100 laboratories in 45 countries, landmark research has, for the first time, shown an association between genetic brain size and neurological conditions such as Parkinson's disease and attention-deficit/hyperactivity disorder (ADHD). And while it doesn't prove causation, it's a big step forward in being able to assess risk factors and provide early intervention.
"There is strong evidence that ADHD and Parkinson's has a biological basis, and this research is a necessary step to understanding and eventually treating these conditions more effectively," said researcher Miguel Rentería, an Associate Professor at QIMR Berghofer.
In the study led by Rentería's Australian institution, 189 researchers looked through DNA data and MRI scans of 74,898 participants from 19 countries. The scientists found 254 genetic variants that affect the size and structure of the human brain, which are also identified as biomarkers for Parkinson's and ADHD.
"Genetic variants associated with larger brain volumes in key brain regions also increase the risk of Parkinson's disease, while variants linked to smaller brain volumes in key regions are associated with an increased risk of ADHD," Rentería explained. "These findings suggest that genetic influences that underpin individual differences in brain structure may be fundamental to understanding the underlying causes of brain-related disorders."
In the largest study of its kind, the scientists looked at the subcortical brain volume of the brainstem, caudate nucleus, putamen, hippocampus, globus pallidus, thalamus, nucleus accumbens, amygdala and the ventral diencephalon. What they found was that genetic expression impacts brain volume across different regions, and this appears to influence a predisposition to various brain-related health conditions.
The areas looked at were chosen for a reason, as they each play a key role in various processes including memory formation, reward and punishment responses, emotional regulation, motor function and sensory communication and processing.
"It brings us closer to answering key questions about how genetics influence brain structure, and how we can potentially treat these conditions in future," Rentería said. "[But] It's worth noting that these are correlations, not causal relationships, and so interpretation must be approached with caution."
The meta-analysis drew from reputable databases including the UK Biobank and ENIGMA (Enhancing Neuro Imaging Genetics through Meta-Analysis), and it provides a window into how genetic expression is tied to mental health. It now provides a springboard for researchers to home in on specific neurobiological conditions and find potential, specific gene linkages.
"By conducting this research all over the world, we're beginning to home in on what has been called 'the genetic essence of humanity,'" said Paul M. Thompson, ENIGMA principal investigator and a professor at the Keck School of Medicine, University of Southern California.