It's an axiom of modern psychiatry that anxiety and depression are two distinct conditions. However, evidence is amassing that they are really two manifestations of one disorder. Looking at them that way, some experts say, could speed the development of drugs that better subdue both conditions.
Surveys have long shown that 60 to 70 percent of people with major depression also have an anxiety disorder, while half of anxiety-disorder sufferers also have symptoms of clinical depression.
Now there's evidence of genetic commonalities between the two conditions. Researchers at the National Institute of Mental Health have found that in people with both panic disorder and depression, there is a significant decrease in a type of receptor (5-HT1A) for the neurotransmitter serotonin. Other studies have shown that the stress response system is overactive in patients with both anxiety and depression. Secretions of the stress hormone cortisol, triggered by repeated trauma, reduce expression of the gene that produces the 5-HT1A serotonin receptor.
"They're probably two sides of the same coin," says David Barlow, director of the Center for Anxiety and Related Disorders at Boston University. "The genetics seem to be the same; the neurobiology seems to overlap. Some people with the vulnerability react with anxiety to life stressors and some, in addition, go beyond that to become depressed."
Anxiety precedes depression developmentally, with anxiety most commonly beginning in late childhood or adolescence and depression a few years later, in the mid-20s. Psychologist Michael Yapko of San Diego targets a flaw in thinking common in both disorders. "The shared cornerstone of anxiety and depression is the perceptual process of overestimating the risk in a situation and underestimating personal resources for coping."
Behavioral geneticist Kenneth S. Kendler of Virginia Commonwealth University in Richmond offers a new way of parsing psychiatric conditions. He sees a small cluster of genetic risk factors creating "internalizing disorders" such as anxiety and depression, which cause sufferers to be miserable. Another set of genetic factors finds expression in "externalizing disorders" such as substance abuse and antisocial behavior—conditions that make others around them miserable.