Genetic studies indicate that TS is inherited as a dominant gene (or genes) causing different symptoms in different family members. A person with TS has about a 50% chance of passing the gene to one of his/her children with each separate pregnancy. However, that genetic predisposition may express itself as TS, as a milder tic disorder or as obsessive compulsive symptoms with no tics at all. It is known that a higher than normal incidence of milder tic disorders and obsessive compulsive behaviors occur in the families of TS patients.

The sex of the offspring also influences the expression of the gene. The chance that the gene-carrying child of a person with TS will have symptoms is at least three to four times higher for a son than for a daughter. In addition, at-risk males are more likely to have tics and at-risk females are more likely to have obsessive-compulsive symptoms. Yet only about 10% of the children who inherit the gene will have symptoms severe enough to ever require medical attention. In some cases TS may not be inherited, and cases such as these are identified as sporadic TS. The cause in these instances is unknown.