How does a parent know if their child or teen is experiencing normal adolescent sadness or moodiness or - a more serious form of depression? The answer may one day lie in a simple blood test, if the results of a new early study are confirmed in larger populations.The results are published in Translational Psychiatry.Early-onset major depressive disorder is a mental illness that affects people under 25. While about 2 to 4% of cases are diagnosed before adolescence, the numbers skyrocket to 10-25% with adolescence, explains lead researcher Eva Redei, professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.Why it matters“Not diagnosed, depression affects how teens relate to others. The No. 1 cause of death among the depressed is suicide,” explains Redei. “If teens are depressed and not treated, there can be drug abuse, dropping out of school. Their whole lives can depend on these crucial and vulnerable years.” Depression typically continues into adulthood, says Redei, so catching it early allows for proper treatment.The researchRedei’s research team discovered eleven blood biomarkers for early-onset major depression. Their original work used rats, and they confirmed their results in this small study of humans that included 14 teens with major depressive disorder, and 14 teens without depression. The researchers discovered that they could distinguish between major depression with anxiety and without anxiety, based upon the genetic markers.“Having an objective test that tells a physician there is a physical, genetic explanation for depression” allows them to treat patients with a precise diagnosis, Redei explains. "Knowing there is an objective reason for their child’s feelings can allow parents and children to understand that depression is an illness, it’s a complicated illness, that is very common, and can be treated.”What's next?She hopes that having a science-based diagnosis will eliminate some of the stigma associated with mental illness. After more testing, these findings hopefully “may help psychiatrists to predict which treatments will be efficient, based on the biomarkers.""It won’t be in the clinic this year, but assuming the resources are available, then it is going to happen.”