title: Tourette's syndrome and associated disorders: a systematic review.
abstract: OBJECTIVE
  To compile data on Tourette's syndrome (TS), tics and associated disorders.
  
  
  METHODS
  A systematic review of the literature was conducted using the 5S levels of organization of healthcare research evidence (systems, summaries, synopses, syntheses, studies), based on the model described by Haynes. The search keywords were Tourette, tics and comorbidity, which were cross-referenced. Studies provided by publishers and articles being processed on July 31, 2013, were also included.
  
  
  RESULTS
  Of all studies retrieved during the search, 64 were selected because they analyzed the epidemiology, clinical features and etiopathogenesis of TS and its comorbidities. TS is classified as a hyperkinetic movement disorder, and at least 90% of the patients have neuropsychiatric comorbidities, of which attention deficit hyperactivity and obsessive-compulsive disorders are the most common. The syndrome is clinically heterogeneous and has been associated with a dysfunction of cortico-striatal-thalamic-cortical circuits involving various neurotransmitters. Although its genetic etiology has been widely studied, other factors may be important to understand this syndrome and its associated disorders.
  
  
  CONCLUSIONS
  TS is a neurodevelopmental disorder that results from the impact of stress factors on a vulnerable biological substrate during the critical periods of neurodevelopment. The study of TS and its comorbidities may contribute, at different levels, to the understanding of several neuropsychiatric disorders of clinical and therapeutic relevance.
authors.affiliation: Coimbra Hospital and University Centre, Coimbra, Portugal.
authors.forename: Bárbara R
authors.initials: BR
authors.lastname: Ferreira
authors.affiliation: Psychiatry Department, Coimbra Hospital and University Centre, Coimbra, Portugal.
authors.forename: J L
authors.initials: JL
authors.lastname: Pio-Abreu
authors.affiliation: Neurology Department, Coimbra Hospital and University Centre, Coimbra, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Januário