title: Prevalence of Tourette syndrome and chronic tics in the population-based Avon longitudinal study of parents and children cohort.
abstract: OBJECTIVE
  Recent epidemiologic studies have demonstrated that Tourette syndrome (TS) and chronic tic disorder (CT) are more common than previously recognized. However, few population-based studies have examined the prevalence of co-occurring neuropsychiatric conditions such as obsessive-compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD). We evaluated the prevalence of TS, CT, and their overlap with OCD and ADHD in the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort.
  
  
  METHODS
  A total of 6,768 children were evaluated using longitudinal data from mother-completed questionnaires. DSM-IV-TR diagnoses of TS and CT were derived using three levels of diagnostic stringency (Narrow, Intermediate, and Broad). Validity of the case definitions was assessed by comparing gender ratios and rates of co-occurring OCD and ADHD using heterogeneity analyses.
  
  
  RESULTS
  Age 13 prevalence rates for TS (0.3% for Narrow; 0.7% for Intermediate) and CT (0.5% for Narrow; 1.1% for Intermediate) were consistent with rates from other population-based studies. Rates of co-occurring OCD and ADHD were higher in TS and CT Narrow and Intermediate groups compared with controls but lower than has been previously reported. Only 8.2% of TS Intermediate cases had both OCD and ADHD; 69% of TS Intermediate cases did not have either co-occurring OCD or ADHD.
  
  
  CONCLUSIONS
  This study suggests that co-occurring OCD and ADHD is markedly lower in TS cases derived from population-based samples than has been reported in clinically ascertained TS cases. Further examination of the range of co-occurring neuropsychiatric disorders in population-based TS samples may shed new perspective on the underlying shared pathophysiology of these three neurodevelopmental conditions.
authors.affiliation: Psychiatric and Neurodevelopmental Genetics Unit, Center for Human Genetics Research, Massachusetts General Hospital, UK. jscharf@partners.org
authors.forename: Jeremiah M
authors.initials: JM
authors.lastname: Scharf
authors.forename: Laura L
authors.initials: LL
authors.lastname: Miller
authors.forename: Carol A
authors.initials: CA
authors.lastname: Mathews
authors.forename: Yoav
authors.initials: Y
authors.lastname: Ben-Shlomo
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D015897:Comorbidity; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D008403:Mass Screening; D009035:Mothers; D009771:Obsessive-Compulsive Disorder / Q000453:epidemiology; D012744:Sex Ratio; D011795:Surveys and Questionnaires; D013981:Tic Disorders / Q000453:epidemiology*; D005879:Tourette Syndrome / Q000453:epidemiology*; D006113:United Kingdom