For an introduction to TS genetics see the first blog post from New York.

Many diseases including movement disorders have been found to be caused by mutations in single genes, for instance Huntington's disease and rare types of young-onset Parkinson's disease. Other diseases also have at least partly a genetic cause which is not yet fully explained, e.g. Tourette's and "normal" late onset Parkinson's. Many diseases probably have a variety of genes that could be involved rather than one single disease-causing gene and TS is almost certainly in this category.

One approach to this is to look for susceptibility genes. These are genetic variations that can be present in normal people but are more likely to be present in people with the disease. There are already a number of known susceptibility genes for Parkinsons.

This new study from Montreal demonstrates a susceptibility gene for people with Tourettes. Of note is that the gene involved, called BTBD9 is also known to be a susceptibility factor for another neurological condition, Restless Legs Syndrome (RLS). There is no strong clinical link between the two conditions although another report from Montreal has suggested some overlap and incidentally it appears that Dr. Georges Gilles de la Tourette himself was aware of the symptoms of RLS.

The treatment for RLS is similar to the treatment for Parkinson's- drugs to boost dopamine brain function, whereas for tics we are normally trying to block dopamine although there have also been trials of Parkinson's drugs in TS. The main point is that dopamine function appears to be a significant factor in both TS and RLS.

The RLS gene was found more in patients without OCD, ie "pure" TS. So, no closer to a gene test for TS or understanding the cause of TS but perhaps another peek into the multiple factors that decide if a person has TS or not.