A genetic study reveals the common and heretofore little-considered roots of psychiatric disorders long considered distinct: a paradigm shift.
A genetic study of data from over a million people highlights the hidden common roots of seemingly disparate psychiatric disorders, which nevertheless share the same biological basis.
According to the research, published on Naturediseases currently considered distinct in diagnostic manuals, such as anxiety and depression, would however have the same “hard core” of genetic variants at their origin, and would therefore fall into the same subgroup. The study could have effects on the classification and prevention of very common and widespread psychiatric disorders.
The hypothesis: five groups of psychiatric disorders
According to scientists at the University of Colorado Boulder (in the United States), 14 important psychiatric disorders can actually be grouped into five main categories, each of which is characterized by the same common underlying genetic risk factors. It means that between many conditions previously thought to be separate, such as autism spectrum disorders and ADHD, there is a much greater overlap than previously believed.
The researchers analyzed the genetic information of over a million people with and without psychiatric disorders contained in various publicly accessible databases, distinguishing five categories of diseases: schizophrenia and bipolar disorder; an “internalizing” category that includes depressive disorders, anxiety disorders, and posttraumatic stress disorder; a category dedicated to neurodevelopmental disorders such as autism and ADHD; a compulsive, which includes obsessive-compulsive disorder and anorexia; and one for substance abuse disorders, such as nicotine addiction and alcohol abuse.
A non-random coincidence
The study was born from the desire to understand why people who already have a diagnosis of psychiatric illness are more likely to receive another one for a new mental disorder. For example, most people with depression also report anxiety disorders, and vice versa. The results obtained suggest that – as explained above Nature – the high prevalence of multiple psychiatric disorders in the same person is not a coincidence, but the reflection of a shared biological basis.
The risk arises in the belly
The researchers then started from these categories to find, reasoning backwards, the regions of the genome whose variations are associated with the genetic risk of developing diseases of at least one of these five macrogroups. They identified 238 of these genomic regions: for example, one of these, on chromosome 11, increases the risk of as many as eight psychiatric disorders because it codes for the genes involved in dopamine signaling, a neurotransmitter crucial for the regulation of mood, drives and rewards.
Many of the genetic factors that link these disorders concern genes involved in fetal development, a phase that evidently has a fundamental role in determining the risk of psychiatric disorders developing in the future.
But there are also specific differences between one macrocategory and another: for example, in the category of anxiety and depression, variants involving oligodendrocytes, brain cells that support and isolate neurons, are more recurrent.
The consequences for patients
The results of the study could influence future classifications of psychiatric disorders: shared biological bases could weigh more and more in the diagnosis and specific symptoms less. On a less theoretical level, all this could be used to help patients suffering from a single pathology to reduce the chances of developing another closely related one, or to identify the categories of drugs most suitable for treating psychiatric disorders of a certain “group”.
