Diagnosing clinical depression in adults is tricky for doctors. That’s mostly because assessment is largely reliant on imperfect analysis, like patient observations and interviews. Most laboratory tests are, by and large, of little use in determining if someone is depressed or not.

That could soon change. About three years ago, a team of researchers co-led by Eva Redei, a research professor for psychiatric disease at the Northwestern University Feinberg School of Medicine, published a study finding that certain RNA markers–a short identifiable string in the DNA sequence, which can be read sort of like fingerprints–were associated with clinical depression in teenagers.

Of the afflicted, some 40% showed improved mental health after treatment.

In a new study published today, that same team has identified nine RNA blood markers that, at very specific levels, could be used to diagnose major depression in adults. Furthermore, three of those genetic fingerprints could be used to determine who might be receptive to cognitive behavioral therapy as a means to get better; the researchers saw consistent patterns in patients for whom therapy was helpful.

Now, the sample size wasn’t huge: The team looked at 32 depressed individual, and another 32 in a control group (the subjects varied greatly in age, from 23 to 83), and put all of them through cognitive behavioral therapy. All the while, researchers kept a close eye on their gene markers.

Of the afflicted, some 40% showed improved mental health after treatment. And after controlling for variables like gender and age, the team found a correlation between nine of the markers in people who were clinically diagnosed as depressed. In the patients who were better after treatment, the team identified three other RNA markers that could be be used for future diagnoses. “We could identify one of those nine, and two others, that were very different between those who got well and those who didn’t,” Redei tells Fast Company. “That shows clearly the efficacy of cognitive behavioral therapy [for certain individuals].”

The methodology wasn’t perfect, but the results were strong enough that “it’s very hopeful for the future,” Redei says. And the team doesn’t yet know how early these gene markers can be detected in, say, children–especially to determine who might be vulnerable to clinical depression as they age. “That’s a huge independent study on its own,” she says.

But for adults suffering from depression? If you can identify who might be receptive to psychotherapy, for example, there may be other unidentified gene markers that can identify who might be receptive to certain types of antidepressants. “What we hope to do,” adds Redei, “is to have an FDA-approved test in the future that any clinical laboratory can do.”