New Insights on OCD and Tic Disorders: Expanding the Genetic Landscape

The development of our brains from prenatal to postnatal stages is a highly intricate process, filled with a range of chemicals, intricate signaling pathways, and the emergence of neural cells. It’s kind of like witnessing a miniature universe unfold.

This complex journey can result in severe conditions, such as obsessive-compulsive disorder (OCD) and chronic tic disorders (CTDs)—including Tourette disorder (TD)—which impact around 2% of the population.

Despite their prevalence, our understanding of the biological underpinnings of these predominantly hereditary disorders has been, well, quite limited—there were only about four “high-confidence” genes previously identified.

That situation has changed significantly. Researchers have conducted an extensive genetic analysis related to the etiology of OCD and CTDs, identifying 36 genes that considerably increase the likelihood of developing one or both of these conditions.

This study “dramatically expands the catalog of shared risk genes, reveals biological connections with autism and schizophrenia and highlights the brain circuits that govern impulse control, movement, and habit formation,” notes Gary Heiman, a genetic epidemiologist at Rutgers University, one of the senior authors of the study.

The research, featured in the journal Nature Neuroscience, detailed a substantial effort by a large team of geneticists and neuroscientists, primarily from Rutgers University. They analyzed both new and previously collected exome data—essentially the part of DNA that encodes proteins—from nearly 4,000 individuals diagnosed with OCD, CTD, or both.

Included in this analysis were over 2,400 parent-child pairs along with more than 1,500 individuals, nearly doubling previous sample sizes.

Interestingly, these two conditions often co-occur; around 50% of those with CTDs exhibit obsessive-compulsive behaviors, while about 30% of those with OCD also have a history of tics.

Using brain maps from humans, macaques, and mice for additional insights, researchers outlined a neural framework for these conditions based on affected brain areas, the timing of risk-associated gene expression, and the types of cells involved.

They gathered more evidence suggesting that these disorders arise from dysfunctions within the cortico-striato-thalamo-cortical circuit—a vast brain loop linked to cognitive processes, impulse control, movement, and information processing.

The research indicated that elevated expression of risk genes is observed at both prenatal and postnatal stages, particularly in key areas like the cortex, striatum, and thalamus.

The cortex serves as the outer layer responsible for essential functions like thinking, learning, and memory; the striatum, located deeper in the brain, influences decision-making and movement; while the thalamus acts as a relay station for various signals.

Moreover, postnatal risk genes are expressed highly in the cerebellum, which coordinates movements and regulates functions like timing and balance.

The study pointed to a specific type of cell—telencephalic projecting excitatory neurons—which play a crucial role in brain signaling and inter-regional communication.

Additionally, researchers observed intricate relationships between these genes and neural pathways. “These genes don’t function in isolation,” explains Jay Tischfield, another senior co-author from Rutgers. “They collaborate within networks. This insight could make it easier to design new therapies focused on entire networks.”

The findings are substantial. These identified genes exhibit strong effects; research indicates an average risk increase of 57 times, with some genes correlating to as high as a 210-fold increase.

Additionally, the study confirmed “substantial genetic overlap between OCD and CTD,” with 30 out of the 36 identified genes linked to both disorders.

Lastly, the researchers noted that several risk genes are also associated with other neurodevelopmental disorders (NDDs), such as autism spectrum disorder, developmental delays, and schizophrenia. This reinforces previous discussions surrounding links between various developmental issues.

Importantly, these genes showed no overlap with congenital heart disease (CHD), which, while inheritable, is not related to neural development.

This research also emphasizes the significance of using retrospective data and acknowledges the long-term dedication of families who provided their DNA samples.

“When we began collecting these samples twenty years ago, we didn’t have the advanced technologies that are available now,” mentions Heiman.

“Families came forward because they wanted to assist scientists in understanding these disorders. Now, with modern genome sequencing, those samples hold immense value.”

The ultimate aim is to create more effective therapies with tailored treatments based on specific genetic or neural pathways for individuals with varying NDDs.

With this expanded knowledge, the possibilities are certainly more promising, as researchers have increased the catalog of large-effect risk genes by tenfold.

“Historically, we were aware of just a couple of potent genes, limiting the pharmaceutical industry’s options for drug development,” Tischfield clarifies.

“Now, having over 30 targets opens up new avenues for treatment advancement.”

This research was published in Nature Neuroscience.