title: Familial clustering of tic disorders and obsessive-compulsive disorder.
abstract: OBJECTIVE
  Tourette syndrome/chronic tic disorder (TS/CT) and obsessive-compulsive disorder (OCD) overlap in their phenomenological features and often co-occur in affected individuals and families. Understanding how these disorders cluster in families provides important clinical information and is an important step in understanding the causes of these disorders.
  
  
  OBJECTIVE
  To determine familial recurrence for TS/CT and OCD using a national epidemiologic sample.
  
  
  METHODS
  We performed a population-based study of national health registries in Denmark, including all individuals (n = 1 741 271) born in Denmark from January 1, 1980, through December 31, 2007, and followed up through December 31, 2013. We identified those with TS/CT and/or OCD.
  
  
  METHODS
  The prevalence of TS/CT and OCD and relative recurrence risk (RRR) for TS/CT or OCD among individuals with an oldest sibling or a parent diagnosed as having TS/CT or OCD compared with individuals without an affected oldest sibling or an affected parent.
  
  
  RESULTS
  In this sample, 5596 individuals were diagnosed as having TS/CT; 6191, OCD; and 412, both disorders. The overall cohort prevalence of TS/CT was 0.42% (95% CI, 0.41%-0.43%) and of OCD, 0.84% (95% CI, 0.81%-0.87%). The mean sibling recurrence risk for TS/CT across all birth years was 9.88% (95% CI, 8.02%-12.16%) and for OCD, 4.01% (95% CI, 2.78%-5.76%). The sibling RRR for TS/CT was 18.63 (95% CI, 15.34-22.63). In contrast, the sibling RRR for OCD was 4.89 (95% CI, 3.45-6.93). The parent-offspring RRR for TS/CT was 61.02 (95% CI, 44.43-83.82), whereas the parent-offspring RRR for OCD was 6.25 (95% CI, 4.82-8.11). The sibling and parent-offspring cross-disorder risks were also significant, ranging from 3.20 (95% CI, 2.22-4.62) to 10.27 (95% CI, 5.17-20.39).
  
  
  CONCLUSIONS
  Tourette syndrome/CT and OCD cluster in families. The familial aggregation of TS/CT is profound and substantially higher than the familial aggregation for OCD. The recurrence risk estimates provide an important clinical framework for identifying individuals at risk and provide insights into the causes of these disorders.
authors.affiliation: Division of Tics, OCD, and Related Disorders, Icahn School of Medicine at Mount Sinai, New York, New York2Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York3Friedman Brain Institute, Icahn School of Medicine at Mount Sin.
authors.forename: Heidi A
authors.initials: HA
authors.lastname: Browne
authors.affiliation: Department of Public Health, Section for Biostatistics, Aarhus University, Aarhus, Denmark.
authors.forename: Stefan N
authors.initials: SN
authors.lastname: Hansen
authors.affiliation: Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York3Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York5Seaver Autism Center for Research and Treatment, Icahn School of Medicine at Mount.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Buxbaum
authors.affiliation: Division of Tics, OCD, and Related Disorders, Icahn School of Medicine at Mount Sinai, New York, New York2Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York3Friedman Brain Institute, Icahn School of Medicine at Mount Sin.
authors.forename: Shannon L
authors.initials: SL
authors.lastname: Gair
authors.affiliation: Children and Adolescent Psychiatric Center, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Judith B
authors.initials: JB
authors.lastname: Nissen
authors.affiliation: Children and Adolescent Psychiatric Center, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Kathrine H
authors.initials: KH
authors.lastname: Nikolajsen
authors.affiliation: Department of Public Health, Section for Epidemiology, Aarhus University, Aarhus, Denmark11Department of Economics and Business and National Centre for Register-Based Research, Aarhus University, Aarhus, Denmark12Lundbeck Foundation Initiative for Integra.
authors.forename: Diana E
authors.initials: DE
authors.lastname: Schendel
authors.affiliation: Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York5Seaver Autism Center for Research and Treatment, Icahn School of Medicine at Mount Sinai, New York, New York8Mindich Child Health and Development Institute, Icahn School.
authors.forename: Abraham
authors.initials: A
authors.lastname: Reichenberg
authors.affiliation: Department of Public Health, Section for Biostatistics, Aarhus University, Aarhus, Denmark.
authors.forename: Erik T
authors.initials: ET
authors.lastname: Parner
authors.affiliation: Division of Tics, OCD, and Related Disorders, Icahn School of Medicine at Mount Sinai, New York, New York2Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York3Friedman Brain Institute, Icahn School of Medicine at Mount Sin.
authors.forename: Dorothy E
authors.initials: DE
authors.lastname: Grice
mesh_terms: D003718:Denmark / Q000453:epidemiology; D005192:Family Health / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D009771:Obsessive-Compulsive Disorder / Q000150:complications / Q000453:epidemiology*; D015995:Prevalence; D012042:Registries; D012307:Risk Factors; D013981:Tic Disorders / Q000150:complications / Q000453:epidemiology*