title: The seroprevalence of antithyroid peroxidase antibodies in bipolar families and bipolar twins: results from two longitudinal studies.
abstract: BACKGROUND
  Previous studies of our group among bipolar offspring and bipolar twins showed significant higher prevalence's and levels of antithyroid peroxidase antibodies (TPO-Abs) in offspring and co-twins (without a mood disorder) compared to controls, suggesting that TPO-Abs might be considered as vulnerability factor (trait marker) for BD development.
  
  
  OBJECTIVE
  Here we elucidate, in the same cohorts, but now after 12- and 6-year follow-up, whether TPO-abs should be considered as a 'trait' marker for BD. The present study aims to investigate whether TPO-Abs (1) are stable over time, (2) are associated with lithium-exposure, (3) share a common genetic background with BD and are related to psychopathology.
  
  
  RESULTS
  In bipolar offspring and twins, the prevalence of TPO-Abs is stable over time (rs= .72 p < .001 resp. rs= .82, p < .001) and not associated with lithium use. At follow-up, an increased prevalence of TPO-abs was again observed in bipolar offspring (10,4% versus 4%) and higher TPO-abs titers were still present in co-twins of bipolar cases compared to control twins [mean 1.06 IU/ml (SD .82) versus mean .82 IU/ml (SD .67)], although statistical significance was lost.
  
  
  CONCLUSIONS
  Although our results show a trend toward an increased inherited risk of the co-occurrence of BD and thyroid autoimmunity, large-scale studies can only draw final conclusions. Nationwide epidemiological and GWAS studies reach such numbers and support the view of a possible common (autoimmune) etiology of severe mood disorders and chronic recurrent infections and autoimmunity, including thyroid autoimmunity.
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands. g.j.l.j.snijders@umcutrecht.nl.
authors.forename: G
authors.initials: G
authors.lastname: Snijders
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: de Witte
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Mesman
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Kemner
authors.affiliation: Department of Psychiatry, Reinier van Arkel, Den Bosch, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Vonk
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Brouwer
authors.affiliation: Department of Psychiatry, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: W A
authors.initials: WA
authors.lastname: Nolen
authors.affiliation: Department of Immunology, Erasmus Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: H A
authors.initials: HA
authors.lastname: Drexhage
authors.affiliation: Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, P.O. Box 85500, Heidelberglaan 100, 3508 GA, Utrecht, The Netherlands.
authors.forename: M H J
authors.initials: MHJ
authors.lastname: Hillegers
keywords: Bipolar disorder; Offspring; Prevalence; Thyroid peroxidase antibodies; Twins