Scientists Find Physiological Markers for Depression and Schizophrenia

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Neuroscientists say they’ve developed a blood test that could help with early diagnosis of depression and schizophrenia. They published their results in the journal Experimental Physiology.

The group of symptoms collectively known as “depression” may result from a variety of causes. Recent studies have linked the illness to genetics, physical differences in the brain, and even an imbalance of gut bacteria. But regardless of what causes it, speedy detection is the key to treatment. Early diagnosis may be even more important in schizophrenia; one 2004 report found that the later a person was diagnosed, the more severe their symptoms would be, and the less responsive they’d be to treatment.

One potential pathway to diagnosis could be a protein called N-methyl-D-aspartate receptor (NMDAR). Brain scans of people with schizophrenia have shown lower-than-average levels of NMDAR activity, while NMDAR-suppressing drugs like ketamine may reduce depression symptoms.

Experiments in animals suggest that NMDAR helps regulate the release of the hormone arginine-vasopressin (AVP). If that’s true in humans, too, reasoned the authors of the new study, then there should be significant differences in the AVP levels of people with depression, people with schizophrenia, and other people.

The researchers recruited people diagnosed with depression and schizophrenia, and a control group of people with no known mental illness. They gave all three groups a dose of saline, which nudged their NMDARs to start releasing AVP, then collected blood samples to test each person’s AVP levels.

As expected, there were significant differences in hormone levels between the three groups—significant enough, the authors say, that they could determine which group a person belonged to just by looking at their results.

Paper co-author Handan Gunduz-Bruce is a psychiatrist and neurologist at Yale School of Medicine. She and her team were pleased with the results, she said in a statement. “This is the first objective, physiological marker for two major psychiatric disorders that, once fully developed into a clinical test, can allow for earlier and more accurate diagnosis, and selection of more appropriate medications for patients.”