As I think (and hope) I've said numerous times throughout this website, genetics is a changing science. Information that was up to the minute a couple of years ago is now terribly out of date.
For example, the main culprit gene in Dr Coming's day (1990) was 4q31, which has since been disproved. Then, on the Genetics page of this website, written about 2006, the main gene was 11q23.
So, when I got the chance to check back into OMIM (the best online resource I've found for this stuff) I was not surprised to see that 11q23 has been relegated to the status of secondary contributing gene.
It now appears a study by Miranda, Wigg, Cabia, Feng, Sador and Barr shows the very palindromic 13q31 position is the area of major concern, specifically the SLITRK1 gene in this region. Since it was announced numerous studies have been done on SLITRK1. While they cannot undoubtedly prove that it is the correct gene yet, they have ruled out a lot of reasons why it wouldn’t be correct.
On OMIM, however, the biggest change has come from the description of the genes themselves. Instead of saying "We think that chromosome position 11q23 is where the problem lies, the current OMIM line is that they have ruled out only half of the human genome in the search for TS, and in fact genes that sit on chromosome 2, 3, 4q, 5, 7, 11 and 17q25 have all been implicated in increasing the severity of GTS conditions.
If I may, smugly, refer back to something I said a couple of years back:
Consider Black eye syndrome:
'Sue' was hit in the eye with a cricket ball, and got a bruise.
'Bob' was bitten by a mosquito next to the eye, and it bruised.
If DSM IV-TR was used, these people would both have "Black-eye syndrome", even though the cause is completely different!
It looks like this parallel is still valid today, if not more so! You can have a mutation at 4q31, or 11q23 or even 5q7 and you may show signs of Tourette’s Syndrome. Even if you share no genetic similarity between you and another person, you can both still have TS.
Now, what this means for the general person on the street with TS, is that you could have a genetic test done on you and your wife, and neither could show a mutation at 13q31, and you could go on to have all TS children.
So, the best way to determine if your child is going to have a GTS symptom is a pedigree after all! A genetic test would have to take into account almost half the human genome, and would take forever!
That's a bit of a blow for genetic engineering on GTS (for the moment) but it does mean that seeing a genetic councilor is currently, and will be for a long time, the best option you have!