We are starting to figure out how psychiatric disorders previously classified solely by symptoms are related to each other (and different from each other) at a biological level in the brain.
"We found that 4 major psychiatric disorders -- major depression, bipolar disorder, schizophrenia, and obsessive-compulsive disorder -- show a surprisingly high level of similarity in their brain structural abnormalities," said Dr. Opel. The shared brain areas showing structural aberrations were mainly in cortical areas associated with cognitive processing, memory and self-awareness.
On the flipside, Dr. Opel added, "we were able to identify regional abnormalities with high specificity for certain disorders." Interestingly, these distinct structural differences sometimes appeared in the same area for two disorders, but in opposite directions from the norm.
In contrast, attention-deficit/hyperactivity disorder and autism spectrum disorder did not share brain structural signatures with any other disorders. That may be because those disorders are considered developmental diseases with a distinct etiology from the other psychiatric conditions, which have more in common.
The researchers do not yet understand the mechanisms behind the shared structural elements, but a growing body of evidence shows that these psychiatric disorders also share common genetic as well as environmental influences, which might underlie the current findings.From Science Daily. The paper and its abstract are as follows:
Neuroimaging studies have consistently reported similar brain structural abnormalities across different psychiatric disorders. Yet, the extent and regional distribution of shared morphometric abnormalities between disorders remains unknown.
Here, we conducted a cross-disorder analysis of brain structural abnormalities in 6 psychiatric disorders based on effect size estimates for cortical thickness and subcortical volume differences between healthy control subjects and psychiatric patients from 11 mega- and meta-analyses from the ENIGMA (Enhancing Neuro Imaging Genetics Through Meta Analysis) consortium. Correlational and exploratory factor analyses were used to quantify the relative overlap in brain structural effect sizes between disorders and to identify brain regions with disorder-specific abnormalities.
Brain structural abnormalities in major depressive disorder, bipolar disorder, schizophrenia, and obsessive-compulsive disorder were highly correlated ( r = .443 to r = .782), and one shared latent underlying factor explained between 42.3% and 88.7% of the brain structural variance of each disorder. The observed shared morphometric signature of these disorders showed little similarity with brain structural patterns related to physiological aging. In contrast, patterns of brain structural abnormalities independent of all other disorders were observed in both attention-deficit/hyperactivity disorder and autism spectrum disorder. Brain regions showing high proportions of independent variance were identified for each disorder to locate disorder-specific morphometric abnormalities.
Taken together, these results offer novel insights into transdiagnostic as well as disorder-specific brain structural abnormalities across 6 major psychiatric disorders. Limitations comprise the uncertain contribution of risk factors, comorbidities, and medication effects to the observed pattern of results that should be clarified by future research.
Nils Opel, et al., "Cross-Disorder Analysis of Brain Structural Abnormalities in Six Major Psychiatric Disorders: A Secondary Analysis of Mega- and Meta-analytical Findings From the ENIGMA Consortium." Biological Psychiatry, 2020; DOI: 10.1016/j.biopsych.2020.04.027