Human Genetics and Obsessive Compulsive Disorder
Since the 1930s, researchers have examined the connection between human genetics and obsessive compulsive disorder (OCD). Although it seems that there is definitely some genetic basis for the disorder, there are also aspects of the environment that can cause symptoms of OCD, perhaps in susceptible people.
Twin and Family Studies
One of the main ways that researchers try to figure out whether a disorder or disease has a genetic basis is by using twin studies. In a twin study, researchers compare the data of a large group of identical/monozygotic (MZ) twins with data from fraternal/dizygotic (DZ) twins. MZ twins have identical genes, whereas DZ twins share only as many genes as regular siblings do. Therefore, if an MZ twin of someone with OCD is at a greater risk of having the disorder than a DZ twin, there is probably a strong genetic component to it.
In the 1980s, Carey and Gottesman published a study in the Archives of Genetic Psychiatry, which studied pairs of MZ and DZ twins, in which one twin of each pair had been diagnosed with obsessive tendencies. This study found a heritability estimate of around 80%, which means that the disorder has a very strong genetic tendency. Other studies followed with similar findings, but these were of limited value for two reasons. First of all, they had no standardized diagnostic criteria to define OCD, and secondly the researchers knew exactly what they were searching for, which prevented them from being "blind" from the results of the study.
Although the diagnostic criteria developed as the years progressed, it wasn’t until decades later that a study was published in Psychological Medicine in which this concern was addressed. This study looked at twins in a national registry and discovered that MZ twins had a significantly higher correlation than DZ twins. Family studies, which are slightly less accurate than twin studies, also seem to show a strong genetic component, although it seems that early-onset OCD is more likely to be familial than late-onset OCD.
A segregational analysis is a technique that researchers use to study the probability of a specific person (or genotype) developing a disorder. Segregational analyses of OCD show that it most likely follows an autosomal dominant pattern of inheritance, but it could also be explained by other genetic reasons.
Researchers are now trying to identify the genes that cause OCD symptoms, in an attempt to understand the risk factors for this disorder. Researchers at both Yale and at the National Institute of Mental Health (NIMH) have discovered that many people with OCD have a genetic mutation in the human serotonin transporter (hSERT) gene, which is involved in transporting the neurotransmitter serotonin from one nerve cell to another. Serotonin helps process information sent through the nerve cells, and then travels back after the signal has been "read." People with this mutation, however, do not send the same amount of serotonin back.
Several other genes, unrelated to serotonin, have been implicated in OCD. These genes include the 5-HT2A-receptor gene, the D2 and D3 (dopamine) receptor genes, and the genes for two enzymes that help metabolize amines. Scientists are still examining the impact of these genetic changes on a person with OCD.
Although the fact that researchers have found these genes may seem to imply that these gene mutations cause OCD, this is not necessarily the case. Even Dr. Ben Greenberg, co-author of a study that found one of these mutations, maintains that it does not reveal the cause of OCD. Instead, it can help scientists begin to understand how genetic mutations affect this disorder and help them begin to search for an effective cure for OCD.
This post is part of the series: Facts and Information About OCD
- Understanding OCD: A Comprehensive Definition of Obsessive Compulsive Disorder
- Types of Obsessive Compulsive Disorder Characteristics
- What are the Best Medications for OCD?
- The Link Between Human Genetics and Obsessive Compulsive Disorder (OCD)
- David Beckham and Donald Trump: Meet the Famous People with OCD