Ask Dr. Ticcy: What is the genetic probability of passing on TS?

Ask_Dr_Ticcy_Logo-238x250Dr. Ticcy is a pseudonym for the Tourette Syndrome Foundation of Canada National Office, which draws on information from experts across Canada and beyond to answer questions from the TS community. Please send your questions to tsfc@tourette.ca with the salutation “Dear Dr. Ticcy.”

Dear Dr. Ticcy,

I am writing to inquire about some information on the genetics of Tourette Syndrome. I look on the TSFC website and the Tourette Blog, and it seems like there are two conflicting stats. On the Tourette Blog, there is a stat that says the probability that genes are passed when with ONE parent has Tourette is 10 percent, but the website states that the rate is 50 percent.

Could you please break this information down for me, as I am kind of confused and am trying to distinguish the genetic probability of Tourette. Thank you!

Confused About Genetics

Dear Confused,

Thank you for reading the Tourette blog, showing interest in the Tourette Syndrome Foundation of Canada’s website, and reaching out with a great question.

How TS is passed on is quite a complex subject. Scientists do not fully understand it yet; however, their understanding is growing with time (and scientific research).

Scientists thought that there might be a specific “TS gene” but recent research suggests that this probably isn’t the case. Instead, it is likely that many genes and non-genetic factors work together to cause TS. Research also suggests that the specific “TS genes” are likely to differ from family to family and individual to individual.

When reading about the inheritance of TS, it is important to remember that there are other tic disorders besides TS (such as chronic tic disorder or transient tic disorder). This means that there is sometimes a difference between having tics and having TS. Put another way: all people with TS have tics, but not all people with tics have TS.

The passage you’re referring to from the “Genetics and Research” section of the TSFC website is about what happens when someone inherits genes linked with TS and the likelihood of passing those on to children.

The first sentence states how likely it is that a person will pass on the “TS genes”: “ A person with TS has about a 50 percent chance of passing the gene(s) to one of his/her children.”

The second sentence explains that inheriting these genes does not always mean a person will have TS. They might have different symptoms like those of chronic tic disorder or OCD. The sentence states: “However, the gene(s) may express as TS, as a milder tic disorder, or as obsessive compulsive symptoms with no tics at all.”

The statistic you read on the Tourette Blog’s “Will My Child Be Born with TS?” was about something a little different. It was referring to the likelihood that someone with TS will have a first degree relative who also has TS: “If you have TS, current research indicates that you have a 5-15 percent chance of having a child, parent or sibling with TS.”

This statistic comes from family studies where scientists try to figure out “how genetic” TS is by examining its incidence among the family members of a person with TS. In sum, the two statistics provide complimentary information about the inheritance of TS. Thank you for your question!

Dr. Ticcy

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