Evidence from genetic studies suggests that TS is inherited in a dominant mode and the gene(s) involved can cause a variable range of symptoms in different family members. A person with TS has about a 50-50 chance of passing on the gene(s) to one of his or her offspring. However, that genetic predisposition may not necessarily result in full-blown TS; instead, it may express itself as a milder tic disorder or as obsessive compulsive behaviors or possibly attention deficit-hyperactivity disorder with few or no tics at all.

It is also possible that the gene-carrying offspring will not develop any TS symptoms. A higher than normal incidence of milder tic disorders and obsessive compulsive behaviors has been found in families of individuals with TS.

Gender also plays an important role in TS gene expression. If the gene-carrying offspring of a TS patient is male, then the risk of developing symptoms is 3 to 4 times higher. However, most people who inherit the gene(s) will not develop symptoms severe enough to warrant medical attention. In some cases of TS, inheritance cannot be determined. These cases are called sporadic and their cause is unknown.