Twin studies are helping shed light on the origins of schizophrenia and bipolar disorder. In a recent Human Molecular Genetics study, researchers suggest the disorders could be caused by environmentally induced epigenetic changes, New Scientist's Andy Coghlan says. Researchers in the UK scanned the genomes of 22 identical twin pairs, in which one individual had been diagnosed with schizophrenia or bipolar disorder. "As expected, the twins had identical DNA. However, they showed significant differences in chemical epigenetic markings," Coghlan says, adding that "these changes were on genes that have been linked with bipolar disorder and schizophrenia." The researchers found differential methylation in several genes previously linked to these disorders. They found that some genes are "over-methylated" in schizophrenia, and "under-methylated" in bipolar disorder, Coghlan adds. "Twins would need to be scanned regularly throughout life to find out whether epigenetic changes precede the onset of the disorders," he says, adding that "it might be possible then to link the alterations to environmental changes such as stressful events or diet, which have been shown to cause inheritable epigenetic changes in mice."