The cross-disorder polygenic analyses also provide evidence for genetic heterogeneity between OCD and TS. First, the polygenic risk scores generated from the individual OCD and TS discovery samples did not predict case-control status of the other disorder. Second, the combined TS/OCD sample was a worse predictor of OCD or TS status than either disorder alone, suggesting that the degree of genetic heterogeneity generated by combining the two phenotypes outweighs any improvement in statistical power due to increased sample size. As noted above, however, we are likely underpowered to detect a modest shared signal, which we have previously identified in this sample using a mixed-model approach (10).
