title: Childhood IQ and risk of bipolar disorder in adulthood: prospective birth cohort study.
abstract: BACKGROUND
  Intellectual ability may be an endophenotypic marker for bipolar disorder.
  
  
  OBJECTIVE
  Within a large birth cohort, we aimed to assess whether childhood IQ (including both verbal IQ (VIQ) and performance IQ (PIQ) subscales) was predictive of lifetime features of bipolar disorder assessed in young adulthood.
  
  
  METHODS
  We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a large UK birth cohort, to test for an association between measures of childhood IQ at age 8 years and lifetime manic features assessed at age 22-23 years using the Hypomania Checklist-32 (HCL-32;n=1881 individuals). An ordinary least squares linear regression model was used, with normal childhood IQ (range 90-109) as the referent group. We adjusted analyses for confounding factors, including gender, ethnicity, handedness, maternal social class at recruitment, maternal age, maternal history of depression and maternal education.
  
  
  RESULTS
  There was a positive association between IQ at age 8 years and lifetime manic features at age 22-23 years (Pearson's correlation coefficient 0.159 (95% CI 0.120-0.198),P>0.001). Individuals in the lowest decile of manic features had a mean full-scale IQ (FSIQ) which was almost 10 points lower than those in the highest decile of manic features: mean FSIQ 100.71 (95% CI 98.74-102.6)v. 110.14 (95% CI 107.79-112.50),P>0.001. The association between IQ and manic features was present for FSIQ, VIQ and for PIQ but was strongest for VIQ.
  
  
  CONCLUSIONS
  A higher childhood IQ score, and high VIQ in particular, may represent a marker of risk for the later development of bipolar disorder. This finding has implications for understanding of how liability to bipolar disorder may have been selected through generations. It will also inform future genetic studies at the interface of intelligence, creativity and bipolar disorder and is relevant to the developmental trajectory of bipolar disorder. It may also improve approaches to earlier detection and treatment of bipolar disorder in adolescents and young adults.
  
  
  BACKGROUND
  None.
  © The Royal College of Psychiatrists 2015. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) licence.
authors.affiliation: , MD, Institute of Health and Wellbeing, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Smith
authors.affiliation: , PhD, Institute of Health and Wellbeing, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Jana
authors.initials: J
authors.lastname: Anderson
authors.affiliation: , PhD, Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University School of Medicine, Cardiff, Wales, UK.
authors.forename: Stanley
authors.initials: S
authors.lastname: Zammit
authors.affiliation: , PhD, Department of Psychiatry & Behavioral Sciences, University of Texas Medical School at Houston, Houston, TX, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Meyer
authors.affiliation: , MD, Institute of Health and Wellbeing, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Jill P
authors.initials: JP
authors.lastname: Pell
authors.affiliation: , PhD, Institute of Health and Wellbeing, University of Glasgow, Glasgow, Scotland, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Mackay