This study has several potential limitations, the most significant of which is the sample size. Although the largest Tourette syndrome GWAS conducted to date, our sample of under 5,000 cases is clearly not yet sufficient to identify definitive Tourette susceptibility variants, as demonstrated by the failure of the top GWAS SNP to replicate in the deCODE sample. Additional potential limitations are also related to sample size, including reduced power to examine additional clinical variables of interest such as age of onset of tics and co-occurring psychiatric illnesses such as obsessive compulsive disorder and attention deficit hyperactivity disorder. However, we anticipate that most, if not all, of these limitations can be resolved by substantial increases in the number of Tourette syndrome cases collected for GWAS, an effort that is currently underway.
