When scientists attempt to define a mental disorder, they can take one of two approaches: View the disorder as a single underlying disease that is expressed through a variety of symptoms or group together a set of disparate symptoms and label them a disorder.
The latter approach is the foundation for the National Institute on Mental Health’s new guiding principles for research on mental disorders, called Research Domain Criteria. The principles will form the basis of an online database of symptom-specific diagnostic categories that researchers will be able to use for designing clinical studies. NIMH hopes to roll out the criteria within the next two years.
One reason for the new system is that the traditional, disease-first model frequently creates situations in which a patient qualifies as having several disorders, says Research Domain Criteria Director Bruce Cuthbert, PhD. “There are certainly people with bipolar disorder who have cognitive dysfunction that overlaps into the range of schizophrenia,” he says. “People don’t think about that because they think about them as separate disorders.”
Confusion over which symptom belongs to which disease can result in a patient’s being eligible for several different treatments — which may or may not alleviate the individual’s symptoms. To address that concern, the Research Domain Criteria will take a symptoms-first approach, looking at the relevant behavioral, neurological and genetic factors and consider the symptom itself to be a diagnosis.
The goal isn’t to supplant the Diagnostic and Statistical Manual of Mental Disorders or the International Classification of Diseases, though, Cuthbert emphasizes. Instead, it’s to provide a tool to help researchers break out of the habit of thinking of symptoms as the result of some disease, when really it’s the other way around.
For example, the DSM and ICD list anhedonia — the decreased ability to experience pleasure — as a symptom typical of a number of disorders including depression, PTSD, eating disorder and schizophrenia. Using current methods, researchers might include a couple of questions about anhedonia on a depression measure, Cuthbert says, but the emphasis of the measure is on diagnosing depression. Instead, he says researchers could just target the anhedonia itself by figuring out what’s wrong with the brain’s reward circuit. Figuring out whether it fits into a larger disorder wouldn’t be as important.
“In the end, the idea is to promote studying multiple levels of analysis to help us understand these disorders better,” Cuthbert says.
If you’d like to be considered to attend a workshop to help NIMH define what belongs in the Research Domain Criteria, send an e-mail, along with a CV and a brief description of your expertise.