Majority of psychiatric disorders have very high comorbidity rates, usually ranging from 70% to 90%. Why? Recent research provides intriguing clues. Psychiatric disorders are so often comorbid because they share common roots. Research into a shared neuropsychopathology factor, often abbreviated as “NP” or “p” factor, indicates that there are common genetic origins, mostly involving genes that regulate astrocyte, microglia and glutamatergic pyramidal neuron function. Furthermore, structural and functional imaging studies suggest that similarities between major psychiatric disorders may be greater than their differences (especially if we take into account inter-personal variations). Similar patterns of brain activity send modified stress signals reverberating through the body, activating common defensive responses (HPA axis, autonomic and immune activation). Consequently psychiatric disorders also share medical comorbidities. Precipitating and perpetuating factors related to mental disorders also tend to be similar: trauma/early life adversity, medical illness, chronic stress, social rejection/isolation/loneliness, etc. These insights are most often not built into clinical practice/research, pharmacological development, where we continue to pursue “clean” diagnostic categories.
Is there a case to be made for “splitting”? There are certain manifestations of mental disorders that have transdiagnostic relevance. Anhedonia, cognitive difficulties, psychomotor retardation and sleep disturbance are examples of symptom domains that might require a personalized/precise and, possibly, a transdiagnostic approach. So should we be “lumping” or “splitting” psychiatric disorders? The answer may be simpler than expected: Yes.
