title: Obsessive-compulsive disorder, tics and anxiety in 6-year-old twins.
abstract: BACKGROUND
  Previous reports of genetic influences on obsessive-compulsive disorder (OCD) symptoms have suggested moderate heritability. Family history studies of co-morbidity have found familial aggregation with tics, especially for early-onset OCD, and familial aggregation with anxiety disorders.
  
  
  METHODS
  Heritability of OCD and familial aggregation of OCD, tics and anxiety disorders were investigated in a community sample of 6-year-old twins using a two-phase design in which 4662 twin pairs were sampled and 854 pairs were assessed in the second phase by maternal-informant diagnostic interview using DSM-IV criteria.
  
  
  RESULTS
  In the multivariate model combined additive genetic and common environmental effects were estimated as 47% for sub-threshold OCD, and the model was unable to distinguish these sources of familial aggregation. There were strong familial aggregations between sub-threshold OCD and tics and between sub-threshold OCD and other anxiety disorders (80% and 97% respectively), although again specific sources could not be distinguished.
  
  
  CONCLUSIONS
  The findings are consistent with the hypothesis of a tic-related early-onset OCD phenotype, but also with the hypothesis of an anxiety-related early-onset OCD phenotype.
authors.affiliation: Institute of Psychiatry, Kings College London, UK. d.bolton@iop.kcl.ac.uk
authors.forename: Derek
authors.initials: D
authors.lastname: Bolton
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
authors.forename: Thomas G
authors.initials: TG
authors.lastname: O'Connor
authors.forename: Sean
authors.initials: S
authors.lastname: Perrin
authors.forename: Thalia C
authors.initials: TC
authors.lastname: Eley
mesh_terms: D001008:Anxiety Disorders / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics*; D002648:Child; D015897:Comorbidity; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D009771:Obsessive-Compulsive Disorder / Q000453:epidemiology* / Q000235:genetics*; D010641:Phenotype; D012931:Social Environment; D020323:Tics / Q000453:epidemiology* / Q000235:genetics*; D013997:Time Factors; D014427:Twins / Q000235:genetics* / Q000523:psychology*