Many psychiatric diseases share genetic roots. A new study, run by researchers at three different laboratories, suggests that rare genetic variations linked to bipolar disorder are also linked to schizophrenia and especially autism.
The study, by researchers at Johns Hopkins School of Medicine, Cold Spring Harbor Laboratory, and the University of Iowa Carver College of Medicine, is among the first to demonstrate the overlap between bipolar disorder and autism.
Despite bipolar disorder’s demonstrated inheritability, pinpointing genes relating to the disease has been exorbitantly difficult. But advances made in medical science recently have allowed scientists to start to figure out which genetic variations affect patients with bipolar disorder.
The researchers behind the study linking autism with bipolar disorder combined a case-control approach with “family-based exome sequencing” to try to discover which genetic variations contribute to bipolar. Case-control approaches look at genetic variants in people who have the disorder compared to people who don’t to figure out which genes increased susceptibility to the disease. The key to this approach is large pools of data.
Family-based exome sequencing is more difficult to perform. Scientists compare all the expressed genes in a genome (known as the exome). The researchers first examine the DNA that encodes proteins (known as exons), and then put that DNA into sequence using computers. This allows technicians to see variants that “travel with” the disease, especially in cases where the disorder is passed from parent to child.
This two-pronged approach identified 84 rare variants in 82 genes that traveled with bipolar disorder. The research team then examined these
84 variants in three case-control datasets of 3,541 individuals with bipolar disorder and 4,774 control patients to figure out which variants predicted the disorder.
Nineteen genes were over-represented in bipolar disorder patients compared to the controls. However, while the data on these genes wasn’t enough to specifically pinpoint the genetic culprits of bipolar disorder, several of the genes were linked to autism and schizophrenia, with autism being especially prominent.
The findings suggest that schizophrenia, bipolar disorder, and autism have similar roots, and are simply different manifestations of similar diseases. The researchers from the study hope that by linking these diseases and finding which genes are responsible, new treatments will be discovered for all of them.