Four distinct psychiatric disorders – autism, schizophrenia, bipolar disorder and depression – have shared gene expression, according to research published online Feb. 8 in the journal Science.
Researchers arrived at the study’s findings by analyzing RNA in 700 tissue samples from the brains of dead people who had autism, schizophrenia, bipolar disorder, major depression or alcohol abuse disorder, then comparing those samples with samples from brains of people without mental illness.
The study looked at patterns of shared gene expression and searched for sets of genes that were activated in each of the disorders. They then looked to see if the sets of genes that were activated were shared across the disorders.
They found a significant overlap in gene expression in four out of five of the disorders: autism, schizophrenia, bipolar disorder and major depression but not alcohol abuse disorder.
The shared pattern was expressed at different levels of intensity across the disorders. Autism had the highest expression, schizophrenia and bipolar a roughly equal lower level and major depression the lowest expression. The authors suggested that this might reflect different severity of illness.
Looking at the specific genes, they found that many of the genes involved the regulation of non-neuronal cells in the brain (astrocytes, microglia, etcetera) and suggested that this finding highlights the role of these cells in regulating how neurons grow and connect.
Finally, although four of the five disorders studied shared a similar pattern of gene expression, major depression showed the greatest divergence from the shared pattern. In major depression genes were activated that were involved in regulating inflammation and they hypothalamic – pituitary – adrenal axis. Consistent with suggestions that depression may reflect a dysregulation of immune and stress response systems.