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Strong heritability among parents, siblings for Tourette, tic disorders

Family members with at least 50% genetic similarity to an individual with a tic disorder are significantly more likely to have a tic disorder themselves, compared with family members with less genetic similarity, according to recently published data in JAMA Psychiatry. 

“Our results indicate that tic disorders, including [Tourette Syndrome] and [chronic tic disorders], are strongly familiar disorders within the Swedish population, and the observed pattern of familiality is consistent with a likely genetic cause. Our heritability estimates place tic disorders among the most heritable neuropsychiatric conditions,” the researchers wrote.

To assess the familial risks and heritability of tic disorders, researchers evaluated data from the Swedish National Patient Registry to identify patients who had been diagnosed with tic disorders from January 1969 through December 2009. 

Results demonstrated that 4,826 individuals had been diagnosed with tic disorders, with the majority (76.2%) being men.

Overall, researchers found a 77% probability of tic disorder inheritance (95% CI, 0.70-0.85). 

The risk of inheriting tic disorders increased substantially with the degree of genetic relatedness. Among individuals with tic disorders, their first-degree relatives were significantly more likely to have a tic disorder (OR = 18.69; 95% CI, 14.53-24.05), compared with second- (OR = 4.58; 95% CI, 3.22-6.52) and third- (OR = 3.07; 95% CI, 2.08-4.51) degree relatives.  

The researchers noted that despite growing up in different environments, first-degree relatives with 50% or more genetic similarities all had comparable risk for inheriting a tic disorder. 

A three-fold increase in risk of having a tic disorder was seen in first-cousin relatives of individuals with tic disorders.

While environment may play a small role in the development of tic disorders, it does not play nearly as big of a role as genes, according to the researchers. 

“The identification of genetic differences in susceptibility to particular environments (gene by environment interactions) in tic disorders will be an important challenge for the future,” the researchers concluded. – by Casey Hower

Disclosure: The researchers report no relevant financial disclosures.