There is very strong evidence that genetic factors play an important role in causing Tourette Syndrome (TS). Compared to dominant and recessive traits where only one abnormal gene can cause a disorder, with TS, complex traits result from the effect of any of a series of genes. This means that in a group of affected individuals, only a few of them will share the same genetic factors that cause their symptoms. It is therefore difficult to identify these factors. To date, genetic studies have considered a number of possible genes and genomic regions potentially responsible for causing TS, but no strong evidence has emerged. Clearly much additional work is needed to identify TS genes. We hope to contribute to the field by focusing our efforts on the French-Canadian population where there is a founder effect. Such populations provide distinct advantages in the search for genes that predispose people to complex traits. In these populations, a relatively small number of ancestors contributed to the actual genetic heterogeneity. In other words, there is a smaller number of incorrect genes that could lead to TS. Therefore, it should be easier to identify one of those. To achieve this goal, we have brought together a multidisciplinary team that includes neurologists, psychiatrists, geneticists and psychologists who have been carefully assessing TS cases using a battery of well-validated instruments. This group constitutes the Montreal Tourette Study Group (MTSG). The identification of a TS gene would provide a critical step in characterizing the disorder and may lead to new insights into the mechanisms involved in the development of TS. Knowing how one specific gene leads to TS makes it easier to search for other similar genes that may also be implicated in the development of the disorder. In addition, finding a gene responsible for causing TS may well lead to improved diagnosis, treatment, and even prevention of this condition. Guy Rouleau, M.D., Ph.D., Montreal General Hospital, Department of Neurology, Quebec, Canada Award: $75,000 This award is supported by a generous donation from Randi Zemsky and Shirley and Sam Zemsky Tourette Association of America Inc. – Research Grant Award 2002-2003