1. Knight T, Steeves T, Day L, Lowerison M, Jette N, Pringsheim T. Prevalence of tic disorders: a systematic review and meta-analysis. Pediatr Neurol 2012;47:77–90.
2. Kurlan R, Como PG, Miller B, et al. The behavioural spectrum of tic disorders: a community based study. Neurology 2002;59:414–420.
3. Hirschtritt ME, Lee PC, Pauls DL, et al. Lifetime prevalence, age of risk, and genetic relationships of comorbid psychiatric disorders in Tourette syndrome. JAMA Psy chiatry 2015;72:325–333.