Pregnant women with altered versions of two genes may be more prone to developing postpartum depression in the weeks following childbirth, researchers from Johns Hopkins University reported Tuesday.

For these women, symptoms of exhaustion, anxiety, and persistent feelings of sadness and hopelessness may develop several weeks after giving birth, lasting weeks, months, even as long as a year. While researchers don't know what causes the condition, a simple blood test may soon predict the illness with a high degree of accuracy.

"Postpartum depression can be harmful to both mother and child," Zachary Kaminsky, an assistant professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine, told media. "But we don't have a reliable way to screen for the condition before it causes harm, and a test like this could be that way."

The researchers identified two genes, TTC9B and HP1BP3, whose epigenetic modifications — which alter the function of the genes without changing the underlying DNA — may be detected in a blood test during any trimester of pregnancy with 85 percent accuracy. With such a warning, clinicians would be able to intervene before depression symptoms became debilitating for the new mother. As many as 10 to 18 percent of new mothers develop the condition, with the rate rising to 30 to 35 percent among women previously diagnosed with mood disorders.

Both genes seem to be "reactive to estrogen," a hormone which had previously been shown to inhibit symptoms of depression, researchers said. However, previous study had also shown levels of estrogen to be similar regardless of depression symptoms in women during the weeks after childbirth.

By studying mice, the researchers found estrogen to be a change agent in cells of the hippocampus, a part of the brain that regulates mood. Kaminsky and his colleagues then devised a statistical model to find the genetic markers that would predict the condition. Although researchers know next to nothing about the two genes implicated here, they suspect the two help to create new cells in the hippocampus and allow the brain to reorganize and adapt in response to environmental change, functions which would both be important to mood.

In a relatively small sample of 52 pregnant women, the Johns Hopkins team then confirmed their findings, noticing a strong correlation between women with postpartum depression symptoms and epigenetic alterations to those two genes highly reactive to estrogen.

"We were pretty surprised by how well the genes were correlated with postpartum depression," Kaminsky said. "With more research, this could prove to be a powerful tool."

To better understand the genetic underpinnings of the condition, researchers must next follow a larger group of pregnant women, for a longer period of time, Kaminsky said. And since epigenetic changes are often transferred to the next generation, researchers wonder whether such alterations to these two genes might appear in children born to mothers with postpartum depression.

If the work holds, women may soon be screened routinely for the condition during pregnancy, allowing clinicians to advise on treatments including antidepressant drugs - though Kaminsky qualified that such drugs must be weighed against potential consequences for both the mother and her unborn child.

"If you knew you were likely to develop postpartum depression, your decisions about managing your care could be made more clearly," he said.

Funded in part by the U.S. National Institute of Mental Health and the Solomon R. & Rebecca D. Baker Foundation, the study was published Tuesday in the journal Molecular Psychiatry.