Mental disorders are archenemies for the human because of their adverse impact on the quality of our life. We, psychiatrists, have been studying them to reveal the real figure and way to overcome any mental disorders.
It may be possible, however, that the archenemies are not multiple, but a single disease, according to some researchers who never form the majority. For example, there is a hypothesis that schizophrenia and bipolar disorder, the two major psychiatric diseases are the same illness. This concept has never been accepted in the academic field. But actually, I sometimes experience some patients who were diagnosed as schizophrenia show the symptoms which are usually seen in those with bipolar disorder.
Therefore, the borders of major psychiatric illnesses are still under discussion. And there are no definite criteria of each mental disorder. Thus, we label them through the clinical symptoms they have. And the symptoms occasionally alter.
Recently, a paper shedding light to this issue was published in Science, a world-famous academic journal. The author suggests that some mental disorders share the same genetic malformations.
The Washington Post: Five major psychiatric disorders have overlapping patterns of genetic activity, new study shows
According to the author, similar levels of particular molecules in the brain was found between autism, schizophrenia and bipolar disorder. Also, bipolar disorder and major depression, and major depression and alcoholism were matched in gene expression.
Science: Shared molecular neuropathology across major psychiatric disorders parallels polygenic overlap
Since rich knowledge is required to understand the concept of this article, I am not sure what the author has really proven. At least, the conclusion of this study seems to be consistent with the clinical findings. Other than schizophrenia and bipolar disorder, schizophrenia and autism are often difficult to be distinguished, major depressive disorder and bipolar disorder as well. Also, most patients with alcoholism suffer from depression. It is not surprising that these diseases share some organic malformations in molecular level.
On the other hand, I believe this issue will never be given decisive conclusion unless current diagnostic criteria are amended. DSM-5 and ICD-10 are excellent manuals for statistics and diagnoses of mental disorders. Nonetheless, there are limitations in classifying any mental disorders strictly. In the next era of psychiatry, some biological markers including genetic patterns will be necessary to diagnose mental disorders.