If only mood rings really worked. With no easy test for mood disorders, doctors must rely on patients’ subjective reports of their emotional states to make a diagnosis. But help may be on the way—researchers have discovered markers of depression and mania in blood, taking a significant step toward developing a blood test for mood.

A team of molecular psychiatrists led by Alexander Niculescu of the Indiana University School of Medicine extracted RNA—genetic material that turns genes on and off—from the blood of people with bipolar disorder. The researchers identified 10 genes that display different patterns of activity during episodes of depression and mania. “We were pleased and surprised to get a blood readout that correlates with symptoms of the illness and things that happen in the brain,” Niculescu says. The changes in genetic activity indicate high and low moods with 60 to 80 percent accuracy.

Five of the genes are involved with myelin, the white matter that insulates neurons and facilitates their communication. Myelin deficits have been associated with schizophrenia and alcoholism, but whether they are a cause or a symptom of these diseases is unknown. Nevertheless, such deficits could serve as a red flag.

“To find particular biomarkers for mental illness is very significant,” says Akira Sawa of Johns Hopkins University, who is searching for similar signposts of schizophrenia.

Broader studies must be done to assess how time, gender and medications may influence gene expression, but Niculescu expects a blood test for mood disorders to be available within about five years. “Having an objective test for a disease state, its severity and especially its response to treatment would be a big step forward,” he says.