By Diane Allingham-Hawkins, PhD, FCCMG, FACMG, Senior Director, Genetic Test Evaluation Program
In recent days, a study by Austrian and German researchers has been widely touted as the first step toward a blood test for depression. The study by Scharinger and colleagues sought to identify a surrogate marker of reuptake of the neurotransmitter serotonin in the brain, a process that is believed to be altered in depression.
Depression, also known as major depressive disorder, major depression, or clinical depression, is defined as a persistent feeling of sadness accompanied by low self-esteem and a loss of interest in activities that would normally be considered enjoyable. Every year, approximately 7% of adults in the United States experience depression and 17% of adults will experience it at some point in their lifetime. Depression is a complex disorder that is likely caused by a combination of physical and emotional factors. This study is specifically focusing on the role that changes in brain chemistry play in depression. Diagnosis of depression currently relies on the depression criteria in the Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association (APA).
The study involved 48 healthy subjects, with no signs or symptoms of depression. It sought to correlate serotonin reuptake in platelets with changes in brain activity. Since serotonin reuptake in brain neurons cannot be measured, the authors theorized that measuring the activity in platelets could be used as a surrogate marker. The authors reported a positive correlation between platelet serotonin reuptake and changes in brain activity in these healthy adults. These findings have lead to speculation that measurement of platelet serotonin reuptake could be used to diagnose depression.
So, is a blood test for depression really on the horizon? No. This is a single study, performed in a handful of healthy subjects. It provides no information whatsoever regarding this relationship in depressed individuals and how that information might be used to diagnose depression. It also ignores other confounding elements, such as risk factors that include alcohol or drug abuse; serious illness; medications; traumatic or stressful events; a family history of depression; and a personal history of anxiety disorder, borderline personality disorder, or posttraumatic stress disorder.
This study needs to be replicated in a larger healthy population to ensure the association is valid. Studies then need to be done in depressed subjects to establish that a similar correlation exists—and show that correlation is distinct from that observed in healthy subjects. Finally, studies are needed to demonstrate that the test can accurately and consistently predict depression in individuals with signs and symptoms of the condition.
While this study may be an exciting first step down the road to a simple blood test for depression, Hayes cautions that much more evidence is needed before the true clinical value of the findings can be determined.