Schizophrenia and bipolar disorder are serious and long-lasting mental illnesses that can have a significant impact on people’s lives. Schizophrenia interferes with thinking and behavior and can lead to psychosis, which results in hallucinations and delusions. Bipolar disorder is characterized by extreme mood swings between depression and mania. Because the condition can cause psychosis, it is difficult to distinguish from schizophrenia.
Scientists studying the DNA outside our genes, known as the ‘dark genome,’ have discovered recently evolved regions that code for proteins linked to schizophrenia and bipolar disorder. According to the researchers, these new proteins can be used as biological indicators to differentiate between the two conditions and to identify patients who are more prone to psychosis or suicide.
Schizophrenia and bipolar disorder are incapacitating mental illnesses that are difficult to diagnose and treat. Despite being one of the most heritable mental health disorders, there are few clues to their cause in the sections of our DNA known as genes.
Researchers believe they may have discovered an explanation in recently evolved regions of the human genome that are not normally recognized as genes but can still code for proteins. The scientists believe that the hotspots in the ‘dark genome’ associated with the disorders evolved because they serve important functions in human development, but their disruption by environmental factors increases susceptibility to, or the development of, schizophrenia or bipolar disorder.
By scanning the entire genome, we’ve discovered regions that aren’t classified as genes in the traditional sense but produce proteins that appear to be associated with schizophrenia and bipolar disorder.
Dr. Sudhakaran Prabakaran
The results are published in the journal Molecular Psychiatry.
“By scanning the entire genome, we’ve discovered regions that aren’t classified as genes in the traditional sense but produce proteins that appear to be associated with schizophrenia and bipolar disorder,” said Dr Sudhakaran Prabakaran, senior author of the report and based at the University of Cambridge’s Department of Genetics at the time of the research.
He continued, saying: “This opens the door to a plethora of new druggable targets. It’s particularly exciting because no one has ever looked beyond genes for clues to understanding and treating these conditions before.”
These genomic components of schizophrenia and bipolar disorder, according to the researchers, are unique to humans; the newly discovered regions are not found in the genomes of other vertebrates. The regions in humans most likely evolved quickly as our cognitive abilities developed, but they are easily disrupted, resulting in the two conditions.
“The traditional definition of a gene is too conservative, and it has diverted scientists away from exploring the function of the rest of the genome,” said Chaitanya Erady, a researcher in the Department of Genetics at the University of Cambridge and the study’s first author.
She continued, saying: “When we look beyond the regions of DNA classified as genes, we see that the entire human genome, not just the genes, has the ability to make proteins. We discovered new proteins involved in biological processes and dysfunctional in disorders such as schizophrenia and bipolar disorder.”
The vast majority of currently available drugs are intended to target proteins that are coded for by genes. The new discovery helps to explain why schizophrenia and bipolar disorder are heritable conditions, and it could lead to new treatment targets in the future.
Schizophrenia is a severe, long-term mental health condition characterized by hallucinations, delusions, and disordered thinking and behavior, whereas bipolar disorder is characterized by extreme mood swings ranging from mania to depression. The symptoms can sometimes make it difficult to distinguish between the two disorders.
Prabakaran left his position at the university earlier this year to start the company NonExomics, which will commercialize this and other discoveries. Cambridge Enterprise, the University of Cambridge’s commercialization arm, has aided NonExomics by licensing the intellectual property. Prabakaran has raised seed funding for the development of new therapeutics that will target proteins implicated in schizophrenia, bipolar disorder, and other diseases. His team has now discovered 248,000 regions of DNA outside of the regions conventionally defined as genes, which code for new proteins that are disrupted in disease.
Natural selection will usually eliminate a gene variant from the population if it severely limits the average number of viable offspring that individuals produce, which is known as reproductive fitness.
One explanation for the persistence of schizophrenia and bipolar disorder is that the genes that increase the risk of these illnesses may also increase reproductive fitness, for example, by increasing creativity in people who carry the genes but do not develop the illnesses.
According to this theory, recent genetic mutations in human evolution allowed us to develop our species’ unique cognitive abilities, but at the cost of increased vulnerability to psychosis.
