Have you ever pondered why we distinctly categorise psychiatric illnesses and neurological disorders, despite both being afflictions of the brain? Mental disorders include illnesses like anxiety, depression, schizophrenia, and bipolar disorder. Neurological disorders, on the other hand, consist of diseases such as strokes, Alzheimer's disease, multiple sclerosis (MS), and migraines.
This division has persisted for more than a century. But does it really make sense?
Brain disorders share genetic risk factors
Researchers at the Centre for Precision Psychiatry at the University of Oslo and Oslo University Hospital endeavoured to explore the genetic causes behind these brain disorders. They posited that if these conditions share genetic underpinnings, they might have more in common than previously assumed.
In a new study, the genes of nearly one million individuals with either a psychiatric or neurological disorder were analysed.
"We discovered that psychiatric and neurological disorders share genetic risk factors to a greater extent than previously recognised. Furthermore, we found that this genetic risk is intimately linked to brain biology," states Olav Bjerkehagen Smeland, psychiatrist and first author.
The shared genetic risk may hold significant implications for patient care. Previous studies have demonstrated that certain treatments can be effective for both types of brain disorders.
The new study has been published in Nature Neuroscience.
Anxiety and migraine share common genetic causes
The researchers noted that some neurological conditions, notably migraine and stroke, share genetic vulnerabilities with psychiatric disorders.
"This implies that some genetic variants may elevate the risk of both stroke and depression, or both migraine and anxiety," explains Smeland.
A genetic variant is a minor alteration in the DNA sequence that can influence everything from our physical appearance to the risk of developing various diseases.
"The findings align with the high comorbidity rates observed between different brain disorders, where individuals are frequently afflicted by multiple conditions," Smeland elucidates.
"We know, for example, that many patients with neurological disorders experience psychological symptoms and illnesses, including depression or psychosis, and that biological factors such as nervous system disturbances play a crucial role in psychiatric illness," he continues.
Could psychotherapy help some people suffering from migraines?
Based on the study, Smeland and his colleagues advocate for a more holistic approach to brain disorders.
"We must ask ourselves whether patients could benefit from an approach that addresses both biological and mental aspects of these diseases, where healthcare providers are equipped with the knowledge and confidence to do so," Smeland emphasises.
Some treatments may be effective for both psychiatric and neurological conditions.
Could, for instance, a greater focus on mental health aid those suffering from migraines?
"Psychotherapy or antidepressant medication could be beneficial to some individuals struggling with migraine. We also know that electrical stimulation of brain regions can assist in treating both Parkinson’s disease and depression," he notes.
"And medications for epilepsy are effective in treating bipolar disorder," the researcher adds.
A myriad of genetic variants shape psychiatric disease risk
Genes and inheritance have long been linked to the risk of psychiatric illness.
"The awareness that some families are more severely impacted by psychiatric disease than others has been present for centuries, yet it is only in the past decade that genetic research in psychiatry has accelerated," says Smeland.
"We now know that genetic vulnerability for conditions such as anxiety and depression is associated with tens of thousands of genetic variants," he explains further.
However, obtaining an accurate diagnosis can be challenging.
"Patients often manifest symptoms associated with various psychiatric disorders. Hence, I believe we should incorporate our growing understanding of biological causes and brain function when determining diagnoses," he says.
Genetic variants affect brain biology in diverse ways
Returning to the extensive genetic analysis of the genes of 1 million patients. The researchers also aimed to understand how genetic variants influence the risk for different brain disorders.
They discovered that this risk correlates with the way genetic variants impact brain biology, although through different mechanisms. The genetic risk for neurological diseases was linked to diverse biological processes affecting the nervous system.
"For instance, genetic susceptibility to stroke was associated with risk factors for thrombosis, while epilepsy was connected to the brain’s nerve cells. The genetic risk for Alzheimer's and MS, conversely, was tied to the immune system, which influences the nervous system," Smeland explains.
In contrast, the genetic risk for psychiatric illnesses was consistently linked to the brain's nerve cells.
"These are the communication cells within the brain crucial for processing and interpreting information, and they significantly impact how we perceive ourselves and the world around us," he notes.
Enhanced knowledge exchange and collaboration may benefit patients
Given the current healthcare system, where different brain disorders are treated by specialists in distinct fields, can patients genuinely receive the optimal treatment?
"Mental health and brain health are closely intertwined, and the clinical manifestations of psychiatric and neurological disorders can be quite complex and interrelated," says Smeland, adding:
"A key question is whether today’s clinical distinctions obstruct a more comprehensive understanding and treatment of brain-related diseases."
However, the goal is not to erase the distinctions between these conditions.
"Although differences remain, I believe that improved knowledge exchange and closer collaboration between psychiatry and neurology could substantially benefit patients."
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Reference
Smeland, O.B., Kutrolli, G., Bahrami, S. et al. A genome-wide analysis of the shared genetic risk architecture of complex neurological and psychiatric disorders. Nat Neurosci 28, 2439–2450 (2025). https://doi.org/10.1038/s41593-025-02090-2?
Centre for Precision Psychiatry
The centre uses big data and novel analytical methods to uncover causes and risk factors in severe mental illness. The aim is to improve prevention and diagnostics, and to develop more targeted treatment.
The centre is led by professor Ole Andreassen.
