For the first time, researchers have uncovered concrete genetic traces of obsessive-compulsive disorder (OCD) in human DNA, bringing us closer to a biological understanding of the disorder.
Sofie is 25 and has battled obsessive thoughts and compulsive actions since her teens. She washes her hands until her skin splits, spends hours checking whether appliances are off and is tormented by constant worries. She feels imprisoned in her own mind.
Sofie has been diagnosed with OCD – but neither she nor her doctors know what set it off or why it stubbornly lingers.
OCD is one of the most common mental disorders, but its causes have long been a mystery. Millions of people live with obsessive thoughts and compulsive behaviour without knowing why. It has long been recognised that heredity plays a role, but it has been unclear exactly which genetic factors are involved.
That is why the latest breakthrough is so striking: for the first time, an international team of 250 researchers has pinpointed 30 spots in human DNA that are clearly linked to OCD. Within these regions they found some 250 genes, of which 25 appear to play a direct role in how OCD takes hold.
The results have been published in the renowned journal Nature Genetics. Nora Strom, the study’s lead author and a PhD student at Humboldt University in Berlin, Germany calls the results a breakthrough in understanding of OCD.
“For the first time, we have created a concrete genetic map that has the potential to significantly improve understanding of the biology of the disease. It is the first step towards earlier, more accurate diagnosis, prevention and treatment that can genuinely help patients,” she says.
The hunt for the first genetic clues
The heritability of OCD is not unusual compared with other mental disorders. Twin studies estimate that the heritability is 40–50%, which means that genetic factors contribute substantially to disorder risk. has been known for a long time, but the exact genes and their location in the genome have been unclear. With tens of thousands of genes in human DNA, finding the right ones has been a huge challenge. That is why 250 researchers worldwide joined forces for this study.
The researchers used a method where they compared the DNA from thousands of people with OCD with the DNA of healthy people. This highlights the stretches of DNA in which certain genetic variants crop up more often in people with OCD.
Two million genomes provided the answer
What makes this study unique is the sheer volume of data. By compiling and reanalysing previous genome-wide association studies – large-scale comparisons of DNA from people with a disorder and healthy individuals – the researchers gained access to genetic information from more than 2 million people, including 53,660 with OCD. The vast dataset enabled even the faintest genetic signals to be detected – clues that would otherwise be lost in the noise.
The researchers found nearly 1,700 small differences in DNA that appear to be significant for OCD. These were spread across 30 areas of the genetic material. When they investigated which genes these differences could affect, the results indicated 251 genes.
Three methods confirm the findings
Of these, 25 stood out as particularly strongly associated with OCD – especially because several independent analyses pointed to these specific genes. Each method provided new insights into how the genetic variants could play a role. The goal was to home in on the most robust associations – genes that cropped up again and again across methods, making them the strongest candidates for driving OCD.
First, the researchers tested entire genes – not just single variants – to determine whether they were linked to OCD, even when other genetic factors blurred the picture. They then investigated whether the same variants affected genetic activity in different tissue types, especially in the brain, where the disease is expected to have an effect.
Finally, they tested whether the same genetic variant both changed how the gene worked and increased the risk of OCD – in other words, whether the link was real and not just a coincidence in the DNA.
Only genes supported by at least two gene-based methods and confirmed by validation tests made it onto the list of 25 likely causal genes. Among them were WDR6, DALRD3 and CTNND1 – all active in the brain and previously linked to mental and neurological disorders. WDR6 appears to be important for impulse control and has previously been linked to disorders such as anorexia and Parkinson’s disease.
DALRD3 helps brain cells translate genetic code correctly – a process that is crucial for brain development. CTNND1 helps to maintain connections between nerve cells – networks that often function differently among people with OCD.
“This study raises more questions than it answers – but for the first time we have solid leads in a field that has long had none,” emphasises Nora Strom.
The immune system’s unexpected link to OCD
A handful of the genes turned up in the major histocompatibility complex region – the part of the genome best known for steering the immune system. That is striking, since this region is usually linked to autoimmune disease and infection – not mental illness.
This is not the first time the immune system has surfaced in psychiatric genetics. Similar patterns have already shown up in studies of schizophrenia and autism. One example from schizophrenia is the C4A gene, in which certain variants decide how many connections between brain cells are kept. This may form a biological bridge between immune function and brain development – and in turn to mental illness.
“Our findings do not prove that OCD is an immune disease, but they raise new questions about how brain development and immune regulation might be linked,” she explains.
If the immune system truly plays a role in OCD – as a driver or a contributor – it could open the door to entirely new treatment options. It might also help explain why many people with OCD show elevated levels of inflammation – a puzzle researchers have long grappled with.
Common genes behind mental disorders
The study also uncovered striking genetic overlap between OCD and other mental disorders, including depression, anxiety and anorexia. Many of the same variants and genes crop up in studies of these disorders – suggesting that they may share underlying biology. Understanding these commonalities better may lead to new forms of treatment in the future that are not tied to traditional diagnoses.
“It is quite possible that the way we classify mental disorders today will not stand in the future. If different disorders share the same genetic and biological traits, we may need to think less in terms of fixed diagnoses and more in terms of the mechanisms behind symptoms,” says Strom.
Nevertheless, she stresses that genetic overlap does not automatically mean a shared cause. One gene may drive one disorder, which in turn can influence another. Only further research can tell what is shared and what is unique.
“This is a long-term project – but a vital one if we are to build more precise, personalised psychiatry in which treatment is tailored to the individual instead of a one-size-fits-all model. Now, at last, we have a foundation to build on,” concludes Nora Strom.
For Sofie and thousands like her, the results offer hope: that future treatments will be more precise – and perhaps begun early enough to halt the disorder before it takes hold.
