potentially resulting in an over-estimate of the heritability if the shared environmental effects are substantial. Conversely, the decrease in variability for the TS phenotype may falsely decrease heritability estimates for TS and perhaps also for CMVT. Similarly, the fact our sample was specifically ascertained for genetic studies rather than being a population-based sample may also affect the heritability estimates, in this case, leading to a potential under-estimate of the heritabilities. In addition, we do not have data on putative environmental contributors to TS, OCD, and ADHD, which are ostensibly accounting for variance not explained by the genetic variance (h2). Despite these limitations, the large sample size and the completeness of the clinical data make it possible to maximize the information available from such a sample in useful and previously unexplored ways.
