In the most extensive genetic study of brain disorders to date, scientists have found a shared genetic basis for psychiatric disorders like schizophrenia and bipolar disorder. But the researchers also found that neurological brain disorders like Parkinson’s and Alzheimer’s disease are more distinct from one another.
The findings may change how scientists look at disorders of the brain, according to the lead author of the study Ben Neale, of the Broad Institute at MIT and Harvard. 
“If we can uncover the genetic influences and patterns of overlap between different disorders, then we might be able to better understand the causes of these conditions — and potentially identify specific mechanisms appropriate for tailored treatments,” Neale said.
The Genetics of Psychiatric Disorders
Published in the journal Science, the findings could also change how psychiatric disorders are categorized, which in turn could inform the development of treatments for patients.
The researchers used a hypothetical example to explain this. It’s possible that a single genetic mechanism affects concentration. This, in turn, could play a role in both the lack of attention that is part of attention-deficit/hyperactivity disorder (ADHD), or the diminished executive function that is a cornerstone of schizophrenia. And the deeply connected nature of psychiatric disorders underscores the need to refine their diagnosis, according to the researchers involved in this study.
Psychiatric and Neurological Disorders
This massive study was led by the Broad Institute and funded in part by the National Institutes of Health, the Orion Farmos Research Foundation and the Fannie and John Hertz Foundation. The work included contributions from researchers at more than 600 institutions worldwide — as well as data from dozens of cohorts including from 23andMe customers who consented to participate in research. The researchers pooled this data to examine more than two-dozen different psychiatric and neurological disorders. In all data from more than a million individuals was used for this study.
“This was an unprecedented effort in sharing data, from hundreds of researchers all around the world, to improve our understanding of the brain,” said coauthor Verneri Anttila, a postdoctoral research fellow in Neale’s lab.
Large Amount of Data Needed for These Studies
The sheer size of this study allowed researchers to discern the sometimes small influence of individual genetic variations on specific conditions. That is because often many dozen or hundreds or even thousands of variants can contribute to risk for specific conditions. The study revealed extensive genetic overlap across different psychiatric disorders in particular between ADHD, bipolar disorder, major depressive disorder, and schizophrenia. The data also indicated strong overlap between anorexia nervosa and obsessive-compulsive disorder (OCD). Some of the findings confirm previous research.
Beyond just investigating the genetic associations that overlapped between conditions, the researchers also looked at the relationship between these conditions and 17 physical and cognitive measures. Among those are such things as the number of years of schooling, personality, smoking habits and BMI. The researchers found significant correlations between more years in school and ADHD, bipolar disorder and depression. But there those same cognitive and personality factors were negatively associated with neurological disorders like Alzheimer’s and Parkinson’s disease, according to the study.
Researchers said that they were surprised to find such a strong correlation between educational attainment and many psychiatric conditions. But the findings point toward potential future studies.
