Obsessive compulsive disorder has many unknowns, including what causes it, why symptoms can differ so much between people, how medication and therapy for it actually work, and why treatment is effective for some people and not for others. In our newly published research, my colleagues and I made a step toward unraveling some of these mysteries by shedding light on the genetics of OCD.
Obsessive compulsive disorder is one of the most impairing illnesses worldwide. Affecting about 1 in 50 people globally, OCD is among the top 10 causes of years lost to disability, leading to harmful effects on a person’s ability to work and function in the world and on their family.
Compared with people without OCD, a person with the condition has a 30% higher chance of dying prematurely from natural causes, such as infections or other illnesses, and a 300% higher chance of dying early from nonnatural causes, such as accidents or suicide.
People with OCD experience obsessions – disturbing, recurrent and unwanted thoughts, fears or mental images – and compulsions, such as repetitive behaviors and rituals performed to ease the anxiety usually caused by obsessions. For example, someone might wash their hands dozens of times or in a specific way to get rid of germs, even if they know it’s excessive or illogical. Avoiding certain places or situations to reduce anxiety or prevent triggering obsessions and compulsions is also common.
People with OCD have compulsions that interfere with their daily lives to a debilitating degree.
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While the exact causes of OCD are unclear, researchers know that both genetic and environmental factors play a role in its development. OCD can run in families; studies attribute between 40% to 65% of OCD cases to genetic factors. OCD that begins in childhood has a stronger genetic influence than OCD that begins in adulthood.
But unlike some genetic diseases caused by a single faulty gene, such as cystic fibrosis or Huntington’s disease, OCD is influenced by hundreds to thousands of genes that each play a small part in disease risk.
My colleagues and I analyzed the DNA of over 53,000 people with OCD and over 2 million people without OCD, the largest study of this kind for this condition. We discovered hundreds of genetic markers potentially linked to OCD – data we hope will ultimately lead to improved ways of identifying people who are at risk for OCD and, down the line, to better treatments.
How scientists study OCD genetics
To find the genes involved in OCD risk, researchers use a method called a genome-wide association study, or GWAS. These studies compare the DNA of tens to hundreds of thousands of people with a disease of interest with the DNA of people without the disease, looking for tiny differences in the genetic material. These genetic markers may be linked to OCD or indicate the presence of other genes linked to the disease.
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