Scientists identify 25 genes that could predict the risk of OCD.

Obsessive-compulsive disorder (OCD) is a psychiatric disorder that is among the most debilitating worldwide, affecting approximately 1 in 50 people. A recent international study, with the participation of the University of Santiago de Compostela (USC), has identified regions of the human genome that increase the risk of developing this pathology.

The research, published in Nature Genetics and led by Dalhousie University (Canada), identified 30 specific DNA regions associated with OCD. From these, 249 genes were studied, of which 25 showed a statistically significant relationship with the development of the disorder. These genetic variants could become future targets for more effective treatments.

“We found that many regions of the genome contribute to OCD risk, and that these regions affect multiple brain circuits, not just a specific area,” explained Manuel Mattheisen, lead author of the study and a Dalhousie University Research Chair.

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OCD is characterized by the presence of obsessions and/or compulsions. Obsessions usually manifest as persistent, unwanted thoughts that generate anxiety or discomfort, while compulsions are repetitive behaviors or mental actions that seek to reduce that tension. Common examples include constant handwashing, the need to repeatedly check things, a fear of dirt, or unwanted thoughts of an aggressive or sexual nature. These behaviors can seriously interfere with the sufferer's daily life.

For years, scientists have explored the role of genes in the development of this condition. Carol Mathews, professor of psychiatry at the University of Florida (UF) and one of the study's lead authors, highlighted in an article published in The Conversation that “OCD can be hereditary; studies attribute between 40% and 65% of OCD cases to genetic factors. OCD that begins in childhood has a greater genetic influence than that that begins in adulthood.”

Unlike monogenic diseases such as cystic fibrosis or Huntington's disease, OCD is influenced by a large number of genes. "OCD is influenced by hundreds to thousands of genes, each of which plays a small role in disease risk," Mathews noted.

One of the most significant findings of this research was the discovery of genetic activity in brain areas involved in functions such as decision-making, planning, emotional control, and error detection. “The genetic markers we found associated with OCD showed elevated activity in several brain regions known to influence the development of the disease,” Mathews explained. These areas are closely linked to emotions such as fear and anxiety, central aspects of OCD.

Another notable finding was the connection between OCD and other psychiatric conditions. Researchers observed genetic relationships between this disorder and Tourette syndrome, anorexia nervosa, anxiety, and depression. Interestingly, they also found a lower genetic predisposition to problematic alcohol use or impulsive behaviors, a finding that, according to the authors, is consistent with the clinical profile of those with OCD, as they tend to avoid risks.

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Beyond the genetic map, the study also pointed to the involvement of certain types of neurons in the development of the disorder. “We found that certain types of neurons, especially medium spiny neurons located in the striatum, were closely associated with genes related to OCD,” Mathews said. These neurons, involved in habit formation, are often linked to the compulsive behaviors typical of this disease. Furthermore, they are common targets for some drugs used to treat it.

Mathews, who directs the UF Center for OCD, Anxiety and Related Disorders, recalled that when he began his career, it was thought that one or two genes were responsible for the disorder. However, over time, it became clear that it is a complex condition involving multiple brain regions and a vast genetic network. “Over time, we have come to realize that OCD is not a disease of a single gene or a specific brain region, but rather a disease of circuits and hundreds of genes that, together, contribute to the development of the disorder,” he explained.

The analysis included genetic studies of more than 53,000 individuals diagnosed with OCD and more than 2 million people without it, making it the largest study of its kind to date. “We discovered hundreds of genetic markers potentially linked to OCD; data that we hope will eventually allow us to better identify people at risk for the condition and, in the future, provide access to better treatments,” Mathews remarked.

In addition to its individual effects, OCD represents a significant public health burden. Mathews noted that the disorder is among the top ten causes of lost healthy life years due to disability, and affects not only the sufferer but also their family and social environment.

“Compared to people without OCD, a person with this disorder is 30% more likely to die prematurely from natural causes, such as infections or other illnesses, and 300% more likely to die prematurely from unnatural causes, such as accidents or suicide,” he explained.

The study also found a possible link to the hypothalamus, a brain region that converts emotions like fear or anger into physical reactions. Although it has not previously been linked to OCD, its inclusion suggests new lines of research into how different brain areas connect to produce the disorder's symptoms.

Finally, Mathews concluded, “With larger studies and continued research, my team and I hope to better link specific biological patterns with individual symptoms. Over time, this could lead to more personalized and effective treatments, improving the lives of millions of people living with OCD worldwide.”

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