Chronic motor or vocal tic disorder is more common than the better-known Tourette's Syndrome. About 1 to 2% of the population is affected. This condition is rare, however, compared to the common short-lived childhood tic (transient tic disorder), which occurs and then stops without treatment within a year. Tics appear to get worse during emotional stress and are absent during sleep. It is thought that all types of chronic tics are variants of Tourette's Syndrome and have an underlying genetic cause. The gene or genes involved have not been discovered yet.
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