A new study suggests that Tourette’s syndrome and other tic disorders appear to be among the highly inherited neuropsychiatric disorders. The study, published online in the June 17 issue of JAMA Psychiatry, shows that tic disorders have a heritability rate of about 77 percent. Study author David Mataix-Cols, PhD, from Karolinska Institutet in Stockholm, Sweden, explained that tic disorders are thought to be highly familial and heritability lacks precise estimates. In this study, they assessed the familial aggregation and heritability of tic disorders at the population level by using data from two Swedish population-based registry studies. From 1969 to 2009 they identified 4826 patients with a diagnosis of Tourette’s syndrome or chronic tic disorder. Results showed that first-degree relatives of patients with tic disorders had an 18-fold increased risk of developing Tourette’s syndrome or chronic tic disorder compared to controls. Second-degree relatives had a 4.5-fold increased risk, and third-degree relatives had a 3-fold increased risk. The risk was similar for close siblings, parents and children of people with Tourette’s syndrome or chronic tic disorder. The results also showed that even when sharing a similar environment, the risk was higher for biological siblings than for those half-blooded in the maternal line. First-generation cousins of patients with Tourette’s syndrome or chronic tic disorder were at three times the risk of controls. The researchers noted that while tic disorders are more prevalent in men, their findings suggest that the familial risk is similar for male and female prior witnesses, regardless of the gender of their relatives. They believe that once tic disorder-related specific genes are identified, they will be associated with tic disorders in both males and females and will have similarly sized effects in males and females, but females may help prevent tic disorders during embryonic and fetal development.