Dopamine Dysfunction in Schizophrenia and Bipolar Disorder: A Review

It can be really difficult to distinguish psychotic bipolar disorder and schizophrenia. Although both are noted for dopamine dysfunction, Dost Öngür makes a compelling argument that they are both more alike than dissimilar by observing pre-synaptic dopamine production. Furthermore, he argues that observations of the underlying biology of these disorders could make for distinction between the two. In this editorial, Öngür compares and contrasts dopamine dysfunction in schizophrenia and bipolar disorder in a paper by Jauhar and colleagues. [1]

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Figure 1: Schizophrenia and dopamine often go hand in hand [Image Link]
First, to set up the cross-sectional study, Jauhar and colleagues obtained a cohort of 60 individuals who had presented to a first-episode psychosis service, 22 of which had bipolar disorder with psychotic features, (disruptions in perception) 16 individuals considered to have schizophrenia, and 22 healthy, normal adults. They co-opted normal PET scans, which uses labeled glucose to identify areas of the brain that metabolize sugars more quickly, and instead used labeled DOPA, a precursor to dopamine, to visually observe areas synthesizing dopamine. What they found was that there was an association between their assay for dopamine synthesis and positive symptom score. More interestingly, they also brought up the idea that disease was unlikely to be predicted by this assay because of a lack of association between duration of disease and their assay. To conclude, Jauhar and colleagues ran a test that looked at dopamine formation and found that the most important correlation was to severity of psychosis symptoms (positive).

Moreover, as the editorial continued, Öngür commented that there was a possibility of evolution of the two disorders, that as time progressed, patients may have crossed-over between psychotic bipolar disorder and schizophrenia in terms of the breadth of their psychosis. I smiled when he commended the authors of the paper on following through with their patients through an 18 month course that tracked the progress of disease. Öngür’s insightful opinion of their work reminds me of the encouragement that I have found in lab, except that this is a case in published work in JAMA Psychiatry. He notes, “This is laudable and mitigates the concern that patients who evolve from schizophrenia to bipolar disorder groups or vice versa could be misclassified for analysis.” [2] I am intrigued by the idea that as mood disorders like schizophrenia and bipolar disorder share so much similarity on a biological scale, that causes presentation for both diseases to look very similar. To conclude, Öngür’s support for the idea of evolution of disease is a curious one, especially when it is linked back to cellular function.

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Figure 2: Bipolar disorder, types 1 and 2 [Image link]
Finally, Öngür closes his piece with a push for clinical distinction between psychotic features and affective features (symptoms that affect mood, emotions, and feeling) based on the idea that the two features are independent of each other. Personally, I would’ve never thought about trying to distinguish two, very closely related disorders in such a way, but this editorial has given me new perspective on the subtleties of diagnoses of mood disorders. I really enjoyed this piece for it’s succinctness and clarity and look forward to reading more from this author.

Bibliography:

  1. [1] Jauhar S, Nour MM, Veronese M, Rogdaki M, Bonoldi I, Azis M, Turkheimer F, McGuire P, Young AH, Howes OD. A Test of the Transdiagnostic Dopamine Hypothesis of Psychosis Using Positron Emission Tomographic Imaging in Bipolar Affective Disorder and Schizophrenia. JAMA Psychiatry. Published online October 11, 2017. doi:10.1001/jamapsychiatry.2017.2943
  2. [2] https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2656681

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