Obsessive-Compulsive Disorder (OCD) and Tourette’s Disorder (TD) are neuropsychiatric disorders, in which genetic factors play a significant part in both.
Obsessive-Compulsive Disorder is characterized by obsessions (unwanted thoughts, images and problematic impulses) and/or compulsions (rituals repeated to alleviate the discomfort caused by obsessions). Individuals with Tourette’s Disorder have one or multiple vocal or motor tics that start before the age of 18 and last more than 1 year.
The high comorbidity rate of Obsessive-Compulsive Disorder and Tourette’s Disorder was documented in previous studies: Of individuals with Tourette’s Disorder, 50% show obsessive-compulsive behaviors, while approximately 20% of individuals with Obsessive-Compulsive Disorder show the symptoms of Tourette’s Disorder. Furthermore, the effect of genetic predisposition has been previously known: Familial and twin studies clearly show the genetic component both for Obsessive-Compulsive Disorder and Tourette’s Disorder.
The first-degree relatives of the individuals affected by Tourette’s Disorder have 10 to 100 times more chance of having Tourette’s Syndrome, compared to the general population. Moreover, both disorders had apparent correlations with other psychiatric disorders. For instance, Obsessive-Compulsive Disorder genetically shows high levels of correlation with anorexia nervosa, bipolar disorder and schizophrenia, while TD is highly correlated with attention deficit disorder/hyperactivity disorder (ADD-HD).
In the past twenty years, many studies have been conducted, seeking a correlation between the serotonergic, glutamatergic and dopaminergic systems in individuals with Obsessive-Compulsive Disorder and Tourette’s Disorder. The serotonergic system has been studied the most in OCD, because selective serotonin reuptake inhibitors (SSRI) are the primary OCD treatment. Moreover, glutamate abnormalities appeared particularly in the cortico-striato-thalamo-cortical (CSTC) circuits.
Studies show that the environmental factors that interact due to genetic predisposition in OCD and Tourette’s Disorder are as important as the genes in the etiology of these disorders. In a population-based study conducted over the environmental risk factors in Tourette’s Disorder and OCD, maternal smoking during fetal growth, preterm delivery, breech presentation, cesarean section and gestation were found to be associated with the development of both Tourette’s Disorder and OCD. Nevertheless, a recent systematic compilation reports that environmental factors can increase the risk only in individuals with a genetic predisposition.
Burton, C. L., Barta, C., Cath, D., Geller, D., van den Heuvel, O. A., Yao, Y., … Zai, G. (2020). Genetics of obsessive-compulsive disorder and Tourette disorder. Personalized Psychiatry, 239–252.