Researchers have found that certain psychiatric disorders like autism, schizophrenia and bipolar disorder share some physical characteristics at the molecular level, specifically, patterns of gene expression in the brain. The findings, published in the journal Science, raise hope for better diagnosis and therapies for people with major psychiatric disorders. "These findings provide a molecular, pathological signature of these disorders, which is a large step forward," said senior study author Daniel Geschwind, Professor at the University of California, Los Angeles. "The major challenge now is to understand how these changes arose," Geschwind said. Researchers know that certain variations in genetic material put people at risk for psychiatric disorders, but DNA alone does not tell the whole story. Every cell in the body contains the same DNA. RNA molecules, on the other hand, play a role in gene expression in different parts of the body, by "reading" the instructions contained within the DNA. The researchers reasoned that taking a close look at the RNA in human brain tissue would provide a molecular profile of these psychiatric disorders. They analysed the RNA in 700 tissue samples from the brains of patients who had autism, schizophrenia, bipolar disorder, major depressive disorder or alcohol abuse disorder, comparing them to samples from brains without psychiatric disorders. The molecular pathology showed significant overlap between distinct disorders, such as autism and schizophrenia, but also specificity, with major depression showing molecular changes not seen in the other disorders. The findings suggest that certain psychiatric diseases are more similar at molecular level than their characteristic symptoms indicate.