Psychiatric disorders such as schizophrenia and bipolar disorder often run in families. In a new international collaboration, researchers explored the genetic connections between these and other disorders of the brain at a scale that far eclipses previous work on the subject.
The results indicate that psychiatric disorders likely have important similarities at a molecular level, which current diagnostic categories do not reflect. The team determined that psychiatric disorders share many genetic variants, while neurological disorders (such as Parkinson’s or Alzheimer’s) appear more distinct.
The results of this study were published in Science 22 June 2018. The team includes researchers from more than 600 institutions worldwide, including University of Helsinki, University of Eastern Finland and several other Finnish research institutes. The study was led by researchers from Broad Institute of MIT and Harvard and Trinity College, Dublin.
Exploring the biological overlap between brain disorders is challenging since the brain is uniquely inaccessible for direct study. And, because brain disorders often co-occur, it’s hard to untangle when one might be affecting the development of another. Thus, in this work, researchers relied on genetics.
For the current study, international consortia pooled their data to examine the genetic patterns across 25 psychiatric and neurological diseases. The dataset ultimately included more than 265 000 patients and 780 000 controls from all consortia studying genomics of common brain disorders that the team could identify.
Because each genetic variant only contributes a tiny percentage of the risk for developing a given disorder, the analyses required very large sample sizes to produce reliable results.
"This study was an unprecedented effort in sharing data, from hundreds of researchers all around the world, to improve our understanding of the brain. The results clearly suggest that groups of genetic variants play a role in multiple disorders, and that psychiatric disorders in particular tend to arise through similar biological pathways,” says the first author of the study, Verneri Anttila, a postdoctoral research fellow at the Broad Institute.
"Based on these results it is possible that some of the symptoms that we have traditionally classified as separate disorders actually tend to arise through similar biological pathways. This kind of knowledge may help us to understand the basic mechanisms behind the symptoms and potentially identify targets for tailored treatments", says Professor Aarno Palotie from the Institute for Molecular Medicine Finland (FIMM), HiLIFE, University of Helsinki, and the Broad Institute.
The final results indicated widespread genetic overlap across different types of psychiatric disorders, particularly between attention-deficit/hyperactivity disorder (ADHD), bipolar disorder, major depressive disorder, and schizophrenia. The data also indicated strong overlap between anorexia nervosa and obsessive-compulsive disorder (OCD), as well as between OCD and Tourette syndrome.
In contrast, neurological disorders such as Parkinson’s and multiple sclerosis appeared more distinct from one another and from the psychiatric disorders — except for migraine, which was genetically correlated to ADHD, major depressive disorder, and Tourette syndrome.
The researchers also examined the relationships between brain disorders and 17 physical or cognitive measures, such as years of education. Surprisingly, genetic factors of some neurological diseases, normally associated with the elderly, were negatively linked to genetic factors affecting early cognitive measures.
Anttila V et al. Analysis of shared heritability in common disorders of the brain. Science. Online June 22, 2018. DOI: 10.1126/science.aap8757
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