New study reveals differences in diagnosis of psychiatric disorders between geographies

Psychiatrists diagnose psychiatric disorders by observing a patient’s symptoms and applying diagnostic criteria, such as those in the Diagnostic and Statistical Manual of Mental Disorders, which is widely used in the United States. However, the diagnostics tests available for psychiatric disorders do not rely on purely objective data, unlike the tests for diseases such as diabetes or conditions like hypertension. As a consequence, the results of a diagnostic test for a psychiatric disorder may be influenced by how the psychiatrist interprets the patient’s symptoms.

While this problem is still prevalent today, we have a few additional tools at our disposal that could soon assist psychiatrists in their diagnoses. For example, genomic studies may be used to identify genes that put a person at a greater risk of developing a specific disorder, although they cannot provide perfect information theoretically. However, genetic correlation analyses have shown that different psychiatric disorders have certain degrees of shared genetic risk. Such were the findings of a recent analysis of the Psychiatric Genomics Consortium datasets, for which scientists calculated the genetic correlations between major psychiatric disorders including schizophrenia, bipolar disorder, and major depressive disorder.

The abovementioned analysis, however, was conducted on a dataset containing samples from mostly Europeans. This motivated a research team led by Professor Masahi Ikeda of the Department of Psychiatry at Fujita Health University School of Medicine, Japan, to compare these genetic correlations with those obtained from an East Asian population. The aim was to determine whether there are any marked differences in the results for Eastern and Western people at large, and discuss what the origin of such differences could be. This study  was co-authored by Takeo Saito and Nakao Iwata, also from Fujita Health University School of Medicine, and published as a research letter in Psychiatry and Clinical Neurosciences on 25 October 2022.

The researchers focused mainly on bipolar disorders (BDs), which can be classified based on the degree of ‘extreme moods’ as BD subtype I (manic and depressive states) and BD subtype II (hypomanic—which is a milder form of manic—and depressive states). The results of the genomic analysis revealed that in the East Asian population, the genes of patients with BD subtype I were more correlated with those for major depression. This was in stark contrast with the results for the European population, for which BD subtype I was more genetically correlated with schizophrenia. On the other hand, the genetic correlations between BD subtype II with schizophrenia and depression were similar when comparing the East Asian and European populations.

But why would there be differences in the genetic correlations of BD subtype I with other disorders between different ethnic populations? This contradicts the common disease—common variant hypothesis, which posits that genetic components typical of a common disease should be shared even among different populations. The research team believes that this difference stems from how Japanese psychiatrists diagnose bipolar disorders. “Japanese psychiatrists tend to be heavily influenced by old German psychiatry and hold that bipolar disorder is a mood problem,” explains Professor Ikeda, “There may thus be a difference in the general diagnostic tendencies between Japanese psychiatrists and Western psychiatrists in that Japanese psychiatrists tend to not diagnose bipolar disorder in patients with delusions or other psychotic features with careful attention.”

Another plausible explanation is that Japanese psychiatrists tend to enroll patients with mood-driven problems more than patients with psychotic features in research on BD. Epidemiological studies on Caucasian populations have shown that patients with psychotic features are half as likely to have BD subtype I, whereas this study on East Asian populations revealed the likelihood to be much lower—as small as 30%.  

The bottom line is that these differences in diagnostic (or ‘enrollment’) tendencies should be noted by psychiatrists when analyzing data, especially the results of clinical trials. “We are not trying to say that either diagnostic approach is superior, but rather that if this trend is also occurring in clinical trials, it may affect evaluations of drug responsiveness,” remarks Professor Ikeda, “This is especially true for second-generation antipsychotics, which are presumed to be more effective for symptoms such as delusions.”

In an accompanying paper, Professor Ikeda and colleagues analyzed the possible influence of these diagnostic trends in clinical trials. Hopefully, further studies such as these will let us accurately use genetic variants as supporting diagnostic criteria for psychiatric disorders.

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Reference

DOI: 10.1111/pcn.13498

About Fujita Health University
Fujita Health University is a private university situated in Toyoake, Aichi, Japan. It was founded in 1964 and houses one of the largest teaching university hospitals in Japan in terms of the number of beds. With over 900 faculty members, the university is committed to providing various academic opportunities to students internationally. Fujita Health University has been ranked eighth among all universities and second among all private universities in Japan in the 2020 Times Higher Education (THE) World University Rankings. THE University Impact Rankings 2019 visualized university initiatives for sustainable development goals (SDGs). For the “good health and well-being” SDG, Fujita Health University was ranked second among all universities and number one among private universities in Japan. The university became the first Japanese university to host the "THE Asia Universities Summit" in June 2021. The university’s founding philosophy is “Our creativity for the people (DOKUSOU-ICHIRI),” which reflects the belief that, as with the university’s alumni and alumnae, current students also unlock their future by leveraging their creativity.

Website: https://www.fujita-hu.ac.jp/en/index.html

About Professor Masashi Ikeda from Fujita Health University
Dr. Masashi Ikeda is a Professor affiliated with the Department of Psychiatry at Fujita Health University School of Medicine. He specializes in interdisciplinary research combining psychiatric disorders with genetics. He has over 200 publications to his name on such topics, with more than 18400 citations. He is also President of Genonics Ltd., a company that offers genetic testing services.

Funding information
This study was supported by the SRPBS from the Japan Agency for Medical Research and Development (AMED) under Grant Numbers JP20dm0107097, JP22wm0425008, and JP22wm0525024; GRIFIN of P3GM from AMED under Grant Numbers JP20km0405201, JP20km0405208, JP22tm0424220; AMED under Grant Number JP22dk0307107; Health and Labor Sciences Research Grant under Grant Numbers 20GC1017 and 21GC1018; JSPS Kakenhi Grant Numbers JP21H02854, JP19K08082, JP18K15497, and JP21K07490; and the Private University Research Branding Project from MEXT. The funders played no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.