Bipolar Disorder Linked To Schizophrenia And Autism Via Common Genetic Roots

New research has shown that bipolar disorder may share some common genetic roots with schizophrenia, autism, and other conditions. The study looked at families that presented a history of bipolar disorder, compared their genomes to previous studies, and came up with some surprising results.

Bipolar disorder has long been linked to other disorders and conditions, including schizophrenia and even increased creativity, as previously reported by the Inquisitr, but the connection has been poorly understood.

This new study aimed to uncover previously unexplored genetic variations that might be the root of bipolar disorder and other conditions. The study was carried out by researchers from the University of Iowa, Johns Hopkins School of Medicine, and Cold Spring Harbor Laboratory, and the results were published recently in JAMA Psychiatry.

According to a press release issued by the study authors, bipolar disorder is considered to be one of the most important psychiatric illnesses due to how common it is. Somewhere between 1 and 3 percent of the population suffers from bipolar disorder, and about a third of them don't respond well to current bipolar disorder therapies.

Finding a genetic cause or trigger for bipolar disorder, the study authors hope, may lead to the creation of new treatments to help that one-third of bipolar disorder patients who don't do well with lithium and other current treatments.

The article abstract that is available from JAMA Psychiatry suggests that bipolar disorder is thought to arise from both common and rare susceptibility alleles, but previous studies have only looked at common variations. This is a problem, according to the study authors, because these common variations aren't likely to be the greatest contributing factors to whether or not someone develops bipolar disorder.

"Common variations are thought to each individually have only a tiny impact. For example, increasing a person's likelihood of getting a disease by 10 to 20 percent," James Potash, the senior author of the study, said via press release. "The hope with rare variations is that they individually have a much bigger impact, like doubling or quadrupling risk for disease."

This study looked specifically at rare variants, which was impossible before the introduction of next-generation gene sequencing techniques. It also focused on eight families who had a history of bipolar disorder due to the fact that the condition is highly heritable and tends to run in families.

The technology that allowed the identification of rare variants within these eight families is known as exome sequencing, and it allowed the researchers to pinpoint 84 rare variants across 82 genes that may be associated with bipolar disorder. The researchers then took that data and looked at genome sequences from thousands of participants in three large case-control data sets and found surprising results.

exome sequencing bipolar disorder
Exome sequencing allowed researchers to identify genetic variants that could cause bipolar disorder. [Photo by Joe Raedle/Getty Images]

The study successfully identified a number of rare variants that are associated with bipolar disorder, which is what they were looking for. However, they also uncovered connections between those same rare variants and other conditions, suggesting a possible link in susceptibility to different mental illnesses.

When they compared the 84 rare variants to the large case-control data sets, the researchers found 19 genes that are likely to be linked with bipolar disorder. They then looked to see if any of those 19 genes had ever been linked to other conditions and found that some of the genes had previously been linked to conditions like autism and schizophrenia.

"It turned out that the schizophrenia and the autism genes were all more represented among our 82 genes than you would expect by chance," Potash said. "And when we looked at our whittled down group of 19 genes, the autism genes continued to be unexpectedly prominent among them."

Although there does appear to be some genetic link between bipolar disorder and other conditions like autism, Potash told the point to any International Business Times UK that it is too early to specific genetic variant as the root cause of either.

"Though we don't have enough statistical evidence to say any single variation is definitively associated with bipolar disorder, these nineteen genes appear over-represented in bipolar disorder cases compared to controls," Potash told IBTimes UK. "By finding the genetic variations involved in bipolar disorder, the hope is we will understand what goes wrong with the brain and how to fix it."

Potash was hopeful that the new study will lead to new and more effective treatments for bipolar disorder, but more work is still needed.

[Photo by Buddhika Weerasinghe/Getty Images]