Researchers at the University of Calgary, Alberta, Canada; University of Toronto, Ontario, Canada; and Dublin, Ireland evaluated the prevalence of tic disorders by using MEDLINE and Embase databases to perform a meta-analysis of reports published 1985- 2011. In 13 studies of children with Tourette syndrome, the prevalence was 0.77%. Boys were affected more often than girls, 1.06% vs. 0.25%. Transient tic disorder, the most common tic disorder, affected 3% children. In adults, the prevalence of Tourette syndrome based on a meta-analysis of 2 studies was 0.05%. The prevalence of tic disorders was higher in all studies performed in special education populations. The current distinction of chronic tic disorders (i.e.. Tourette syndrome, chronic motor tic disorder, and chronic vocal tic disorder) into separate categories is of debatable value. Except for the socially disabling effects of vocal tics, few differences are likely between chronic tic disorders in their etiology and response to therapy. 
COMMENT. Meta-analysis reveals that tic disorders are more common in children than in adults, in special education populations than in general populations of children, and among boys more than among girls. Transient tic disorders are the most common type of tic disorder in children, followed by chronic tic disorders and Tourette syndrome. The higher prevalence of tic disorders in boys than in girls (4:1) is a similar gender difference to that in other developmental disorders, such as autism (4 boys to 1 girl) and ADHD that affects boys 3-6 times more often than girls.