Studies have shown there is a link to TS being genetic. However, it's also noted that it
doesn't manifest itself in every family member. In fact, some families have multiple
siblings, as well as adults and several generations with TS, while others may only have
one sibling with TS and even skip a generation to find another.
Although there may be a few genes with substantial effects, it is also possible that many
genes with smaller effects and environmental factors may play a role in the development
of TS. Genetic studies also suggest that some forms of ADHD and OCD are genetically
related to TS, but there is less evidence for a genetic relationship between TS and other
neurobehavioral problems that commonly co-occur with TS. It is important for families to
understand 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. It is also possible that the gene-carrying offspring will not develop any TS
symptoms.
The sex of the person also plays an important role in TS gene expression. At-risk males
are more likely to have tics and at-risk females are more likely to have
obsessive-compulsive symptoms.
People with TS may have genetic risks for other neurobehavioral disorders such as
depression or substance abuse. Genetic counseling of individuals with TS should include
a full review of all potentially hereditary conditions in the family.