An excavation of a million people's genes has provided some interesting clues to how several common psychiatric disorders might arise, including major depression and schizophrenia. And it's also highlighted connections between some mental illnesses and other health problems, including heart disease.
Illustration: TheDigitalArtist (Pixabay)
An international group of researchers from the US, UK, China, Singapore, Japan and Australia collaborated for the project, dubbed the Brainstorm Study. They pooled together genetic data from 265,000 patients diagnosed with one of 25 different brain disorders, and compared it to genetic data of 785,000 people with no such diagnosis.
Most of the disorders included were conditions thought to be psychiatric in nature, but they also included neurological disorders such as Alzheimer's disease and multiple sclerosis, as well as migraines, epilepsy and stroke.
People with different neurological disorders did not have significant genetic patterns in common with one another, or with people who had psychiatric illnesses.
But the same wasn't true among people with psychiatric illnesses. In particular, people who either had anorexia nervosa, obsessive-compulsive disorder or schizophrenia had the most genetic overlap with one another. And people with schizophrenia tended to share a lot in common genetically with people who had other mental illnesses, such as depression.
People with depression also had many similar genetic patterns with those who had bipolar disorder and attention-deficit/hyperactivity disorder (ADHD).
The study, published this week in Science, is the largest of its kind, according to the authors.
"This work is starting to reshape how we think about disorders of the brain," senior author Brian Neale, director of population genetics in the Stanley Center at MIT's Broad Institute as well as a researcher at Harvard and Massachusetts General Hospital, said in a statement.
"If we can uncover the genetic influences and patterns of overlap between different disorders, then we might be able to better understand the root causes of these conditions - and potentially identify specific mechanisms appropriate for tailored treatments."
A person's genetics are, of course, only a small part of why they might develop a mental illness. And an individual genetic variation linked to mental illness amounts to a tiny drop in the bucket when it comes to risk.
But by looking at as many as risk-associated genes as possible at the same time, the researchers say, we can better understand how and why mental illness happens in the first place.
The findings here suggest, as other recent studies have, that there's no clear border between certain mental illnesses. Many of the same genes that make your brain vulnerable to depression also make it susceptible to schizophrenia, for example.
These genes (and other factors such as our environment) could affect how the brain functions in more than one way, accounting for the different manifestations of mental illness.
But many psychiatric disorders could still share some common traits caused by similar dysfunctions in the brain, such as the lack of concentration seen in both people with ADHD and schizophrenia. The research also suggests a person's brain can be harmed through different means and cause similar symptoms, such as the psychosis seen in people with late stage Alzheimer's and schizophrenia.
"The tradition of drawing these sharp lines when patients are diagnosed probably doesn't follow the reality, where mechanisms in the brain might cause overlapping symptoms," said Neale.
The study also reaffirms some previous research looking at the connections between our physical and mental wellbeing. People who had stroke or heart disease were more likely to have genes associated with major depression, for instance.
And people with higher attained education level or reported intelligence had a greater genetic risk for several disorders, such as anorexia nervosa, autism spectrum disorder and bipolar disorder, while a lower attained education level was associated with a greater risk for ADHD, depression and anxiety.
"These results suggest the existence of a link between cognitive performance in early life and the genetic risk for both psychiatric and neurological brain disorders," the authors wrote.
The connection between a person's education level and certain brain disorders might share be related to a common genetic origins, but it might also reflect that early, potentially changeable life factors can have long-lasting effects on mental and neurological health.
People who do poorly in school, for instance, have been shown to be more likely to develop Alzheimer's, while higher education seems to have a preventative effect.
The researchers plan to keep studying these questions, hopefully by using even larger data sets of people's genes.