Mental health
Bipolar disorder may share genetic roots with autism iStock

Bipolar disorder may share genetic roots with autism, scientists have found. This discovery adds on to a growing body of scientific literature which suggests the existence of genetic overlaps between different mental disorders.

The study, published in JAMA psychiatry, aimed to pinpoint rare genetic variations involved in the onset and development of bipolar disorder. Scientists know bipolar disorder unfolds in the brain, but they do not exactly understand what it is that goes wrong.

Likewise, it has been difficult to isolate specific gene variants that contribute to the illness, even though there has been increasing evidence that the disorder is highly heritable.

Using modern technologies, the study's authors were able to identify a number of rare variants shared by people with bipolar disorder. Additionally, they discovered that a number of these variants had been associated before to other diseases, such schizophrenia and autism.

Gene-sequencing technology

First, the scientists focused on eight families in which bipolar disorder ran, and the idea was to see whether they presented rare genetic variations that could be linked to the disease.

For this purpose, the researchers used a modern gene-sequencing technology called Exome sequencing. This allowed them to distinguish 84 rare variants in 82 genes. These variations were also predicted to damage proteins, incorrectly coded by the mutated gene.

Then, the 82 genes and 84 variations were crossed-referenced with three large case-control datasets that included genome sequences from a total of 3,541 individuals with bipolar disorder and 4,774 control patients. The scientists found that 19 of the 82 genes identified previously were present in greater proportions that would be expected by chance among bipolar individuals.

"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", co-senior author James Potash of the University of Iowa 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."

Autism genes

The scientists also investigated if any of the nineteen genes had been implicated before in other disorders. They found an over-representation of genes linked to autism. "Among the nineteen bipolar disorder genes implicated, there were a surprising number of genes that had previously been found in autism, suggesting an overlap in susceptibility to the two illnesses", Potash says.

On the long-term, this new understanding of the genetic drivers of bipolar disorder, and how the disease relates to autism, could lead to the development of new strategies and treatments.

"It is an exciting time to work in this field. For twenty-five years we have struggled to get results, Now thanks to new technologies we are able to identify genetic variations in psychiatric disorders, and we believe this could lead us to really move towards a better understanding of the nature of these diseases", Potash concludes.

The research was conducted by scientists from the University of Iowa Carver College of Medicine, Johns Hopkins School of Medicine, and Cold Spring Harbor Laboratory.