Is Obsessive Compulsive Disorder Genetic?

With the human genome having finally been mapped out, the search is on for those genes that cause us to develop illnesses, including obsessive-compulsive disorder (OCD). Although it is clear that OCD has a genetic basis, it is not yet clear which genes may be important and under what circumstances.

Genes and Illness

Before discussing whether there is a genetic basis for OCD, let’s review some basic genetic concepts and how they relate to illness.

Genes act as the body’s blueprint for making different proteins. These proteins are used to manufacture an enormous number of tissues and biochemicals. Interestingly, different people can have different versions of a given gene. These different versions are sometimes called alleles.

While some diseases like cystic fibrosis are thought to be caused by one specific gene, most diseases, including mental illnesses like OCD, are thought to be caused by a combination of many different genes. In these cases, your vulnerability to a given disease depends on the different versions or alleles of the genes you inherited from your parents and in what combination.

Environment Plays a Large Role in Illnesses Developing

However, it is important to realize that the environment has a very strong influence on whether a particular genetic vulnerability is able to express itself in the form of an illness. For example, a person who is genetically vulnerable to lung cancer may only develop the disease if they smoke cigarettes or they are exposed to heavy environmental pollution. In another instance, a person who is vulnerable to depression may never become depressed if they don't ever encounter a severe enough stressor.

Although we often hear about the “nature versus nurture” debate, most experts now recognize that it is the interaction between our genes and the environment that determines whether we develop an illness. Indeed, it is often said that while our genes "load the gun," it is the environment that "pulls the trigger."

The Genetics of OCD

Research using identical twins and the relatives of people with OCD suggests that the greatest factor in a person’s risk for developing OCD is genetic, with the remaining risk being determined by the environment. Given this, researchers have been searching for the specific genes that create a risk for developing OCD.

For example, there is some preliminary evidence that having particular versions or alleles of genes controlling the manufacture of serotonin (a neurochemical that may be important for OCD), brain-derived neurotrophic factor (a chemical that plays a large role in controlling development of the brain) and glutamate (another neurochemical in the brain that could be important for OCD) may reflect some sort of vulnerability to developing OCD. That said, it is far from clear how these genes influence the development of OCD, and there is plenty of research that still needs to be done.

Genetic Vulnerability Means Little Without Environment

In addition, it is important to keep in mind that these (and other, as of yet undiscovered) genetic vulnerabilities may only be relevant under the right environmental conditions. For example, OCD is associated with prenatal risk factors, such as gaining too much weight while pregnant and difficult labor, as well as life stressors, such as significant emotional or physical abuse. As such, someone may not develop OCD unless they possess the right genetic vulnerability under the right (or wrong, perhaps) circumstances.

OCD is a very complex illness. It is very unlikely that a single gene out of the roughly 30,000 we possess could ever be responsible for generating the complex obsessions and compulsions that are characteristic of OCD. It is much more likely that OCD is the result of many different genes interacting to create an increased vulnerability.

Studies of the genetics of OCD are currently focusing on genetic differences that might explain the different OCD symptom subtypes that exist. Such research could be helpful in developing treatments that are able to target specific symptoms with greater effectiveness than is currently possible.