To date, most of the work aimed at elucidating the genetic causes of TS and OCD has focused on candidate gene studies and linkage analyses; a few studies examining chromosome abnormalities and copy number variants (CNVs) have also been reported (11–14). Recently, our group performed genome-wide association studies (GWAS) of TS and OCD, and for each disorder identified a number of genes and genomic regions of interest, most with modest significance levels. Here we report GWAS results for a combined sample of individuals with TS, OCD or TS+OCD, along with analyses aimed at elucidating the genetic architectures and genetic relationships between the two disorders. Combining these heterogeneous but related phenotypes in joint analyses could have one of two potential effects: 1) enhancement of the genetic signal as a consequence of increased power due to adding samples from genetically-related phenotypes; 2) reduction of the genetic signal as a consequence of increased genetic heterogeneity, outweighing potential benefits of increased sample size. Either way, given the prior evidence supporting shared genetic factors, and the lack of definitive susceptibility genes for either disorder, joint analyses of TS and OCD cases represent an important advance toward understanding the underlying causes of these common neuropsychiatric disorders.
