 Older estimates "came from tertiary referral samples, the sickest of the sick"; greater prevalence casts the condition in an entirely new light, and calls for new biological models of the condition and new approaches to addressing a more common disorder.Discovering the causes of Tourette's may help resolve the questions of what it is and who has it.The autosomal dominant inheritance model has not been validated, and past research has been affected by the problem of referred samples, which may not reflect broader populations of persons with Tourette's.