 Tourette's patients are often recruited from sources that introduce ascertainment bias towards one 'type' of TS.Developing and applying standardized instruments, along with a greater awareness of ascertainment bias in recruitment sources, will be important in genetic studies.We do not know if "we lose both signals and are just adding noise to the experimental outcome" when comorbid conditions, such as OCD or ADHD, are included or excluded from study samples, or samples include/exclude children or adults, or patients with severe symptoms.