Shared White Matter Biomarker Identified in Schizophrenia and Bipolar Disorder
Researchers identified shared white matter alterations in the corpus callosum as a common biomarker across schizophrenia and bipolar disorder, supporting the concept of a psychosis spectrum rather than distinct disorders.
Researchers have identified a shared biomarker between schizophrenia and bipolar disorder, two psychiatric conditions historically treated as distinct and unrelated. The discovery highlights shared white matter alterations in the corpus callosum, a brain structure that connects the brain's left and right hemispheres, observed across the entire psychosis spectrum rather than being limited to a single diagnosis.
For decades, schizophrenia and bipolar disorder were treated as distinct and unrelated psychiatric disorders. Schizophrenia is a psychiatric disorder characterized by altered thinking and emotional patterns, hallucinations, false or irrational beliefs (i.e., delusions), cognitive deficits, and disorganized speech. Bipolar disorder, on the other hand, is marked by extreme mood swings, ranging between periods of high-energy (i.e., mania or hypomania) and depressive episodes.
While the symptoms of schizophrenia and bipolar disorder are markedly different, many patients diagnosed with either of these conditions experience psychosis at least once in their lifetime. Psychosis is a mental state that causes people to lose touch with reality, experiencing hallucinations, delusions, disorganized speech, and irrational thinking patterns.
More recently, studies found that patients diagnosed with schizophrenia and bipolar disorder sometimes share other overlapping symptoms, as well as common patterns in their genes and brain organization. This inspired the idea that these disorders are part of a shared psychosis spectrum, which would explain their common features and characteristics.
Researchers at University of Florence, Geneva University Hospital, and École Polytechnique Fédérale de Lausanne reviewed and analyzed the findings of previous studies to further test this hypothesis and validate the existence of a psychosis spectrum of disorders. Their paper, published in Nature Mental Health, outlines common brain features in patients with schizophrenia and bipolar disorder, particularly differences in the integrity of white matter.
Over the past years, increasing evidence has shown that conditions such as schizophrenia and bipolar disorder share many biological features, including genetic risk factors and brain alterations, suggesting they may lie along a common psychosis spectrum rather than being completely distinct illnesses. Most past neuroimaging studies focused on either schizophrenia or bipolar disorder, rather than comparing the two.
The researchers systematically reviewed brain imaging data collected by different teams of neuroscience and mental health researchers over the past 30 years. All this data was collected using magnetic resonance imaging (MRI), a non-invasive imaging technique that allows scientists to obtain 3D images of the brain and infer properties of white matter connections. These connections act like information highways, enabling different brain regions to communicate efficiently.
In total, the analysis combined data from 96 studies involving thousands of participants with psychosis spectrum disorders and healthy controls. The researchers focused on two well-established measures of white matter structure that reflect how organized and intact these brain pathways are.
The researchers collectively analyzed the results of several studies, looking at schizophrenia and bipolar disorder both individually and together, all while also accounting for differences in age and sex. This allowed them to identify brain regions that appear to be similarly affected in patients with either of the two disorders.
The findings remained significant, and in some cases became clearer, after accounting for age and sex, suggesting they are unlikely to be explained simply by illness duration or aging. This supports the idea that disruptions in brain connectivity may represent a core biological feature of psychosis.
The results of this meta-analysis pinpoint a candidate biomarker that appears to characterize both schizophrenia and bipolar disorder. This finding may provide new insights into the underlying mechanisms of these mental health conditions and could influence future research into diagnosis and treatment strategies.