CoChat
Sign Up
Cited by 102Schizophrenia research and treatmentGenetic Associations and EpidemiologyCognitive Abilities and Testing

IQ and Schizophrenia in a Swedish National Sample: Their Causal Relationship and the Interaction of IQ With Genetic Risk

Open access
Kendler, Kenneth S., Ohlsson, Henrik, Sundquist, Jan, Sundquist, Kristina·2015·American Journal of Psychiatry
DOI 10.1176/appi.ajp.2014.14040516PMC PMC4391822
Open this paper in CoChat — free account

Abstract

OBJECTIVE: The authors sought to clarify the relationship between IQ and subsequent risk for schizophrenia. METHOD: IQ was assessed at ages 18-20 in 1,204,983 Swedish males born between 1951 and 1975. Schizophrenia was assessed by hospital diagnosis through 2010. Cox proportional hazards models were used to investigate future risk for schizophrenia in individuals as a function of their IQ score, and then stratified models using pairs of relatives were used to adjust for familial cluster. Finally, regression models were used to examine the interaction between IQ and genetic liability on risk for schizophrenia. RESULTS: IQ had a monotonic relationship with schizophrenia risk across the IQ range, with a mean increase in risk of 3.8% per 1-point decrease in IQ; this association was stronger in the lower than the higher IQ range. Co-relative control analyses showed a similar association between IQ and schizophrenia in the general population and in cousin, half-sibling, and full-sibling pairs. A robust interaction was seen between genetic liability to schizophrenia and IQ in predicting schizophrenia risk. Genetic susceptibility for schizophrenia had a much stronger impact on risk of illness for those with low than high intelligence. The IQ-genetic liability interaction arose largely from IQ differences between close relatives. CONCLUSIONS: IQ assessed in late adolescence is a robust risk factor for subsequent onset of schizophrenia. This association is not the result of a declining IQ associated with insidious onset. In this large, representative sample, we found no evidence for a link between genius and schizophrenia. Co-relative control analyses showed that the association between lower IQ and schizophrenia is not the result of shared familial risk factors and may be causal. The strongest effect was seen with IQ differences within families. High intelligence substantially attenuates the impact of genetic liability on the risk for schizophrenia.

The claims and statistics of this paper haven’t been checked yet.

Run the check — free, no account needed. It reads the open-access text and checks the sources it cites.

A few free checks a day · papers already verified open instantly · results are public

Integrity signals

Registry

Crossref · 10.1176/appi.ajp.2014.14040516

Cites

2 of 2 references verified0 citation errors · 0 not checkable

Statistics

Claims the paper makes

The claims and statistics of this paper haven’t been checked yet.

Run the check — free, no account needed. It reads the open-access text and checks the sources it cites.

A few free checks a day · papers already verified open instantly · results are public

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

The self-check needs the paper’s full text.

Cites

Flagged first, then by citations

Research works printed but not linked: 26

  1. [1]Aylward E Walker E Bettes B Intelligence in schizophrenia: meta-analysis of the research Schizophr Bull 1984 10 3 430 59 6382590
  2. [2]Woodberry KA Giuliano AJ Seidman LJ Premorbid IQ in schizophrenia: a meta-analytic review Am J Psychiatry 2008 5 165 5 579 87 18413704
  3. [3]Khandaker GM Barnett JH White IR Jones PB A quantitative meta-analysis of population-based studies of premorbid intelligence and schizophrenia Schizophr Res 2011 11 132 2-3 220 7 21764562 PMC3485562
  4. [4]Slater E Cowie V The Genetics of Mental Disorders London Oxford University Press 1971
  5. [5]Milne BJ Moffitt TE Crump R Poulton R Rutter M Sears MR Taylor A Caspi A How should we construct psychiatric family history scores? A comparison of alternative approaches from the Dunedin Family Health History Study Psychol Med 2008 12 38 12 1793 802 18366822 PMC3752774
  6. [6]Risch N Estimating morbidity risks in relatives: the effect of reduced fertility Behav Genet 1983 9 13 5 441 51 6667223
  7. [7]Kendler KS MacLean CJ The impact of altered fitness on the risk of illness in relatives Genet Epidemiol 1989 6 4 481 91 2777069
  8. [8]Rothman KJ Greenland S Lash TL Modern Epidemiology Third Philadelphia, PA Lippincott Williams & Wilkins 2008
  9. [9]Kendler KS Gardner CO Interpretation of interactions: guide for the perplexed Br J Psychiatry 2010 9 197 3 170 1 20807958
  10. [10]Trull TJ Sher KJ Minks-Brown C Durbin J Burr R Borderline personality disorder and substance use disorders: a review and integration Clin Psychol Rev 2000 3 20 2 235 53 10721499
  11. [11]Tiihonen J Haukka J Henriksson M Cannon M Kieseppa T Laaksonen I Sinivuo J Lonnqvist J Premorbid intellectual functioning in bipolar disorder and schizophrenia: results from a cohort study of male conscripts Am J Psychiatry 2005 10 162 10 1904 10 16199837
  12. [12]Isohanni I Jarvelin MR Jones P Jokelainen J Isohanni M Can excellent school performance be a precursor of schizophrenia? A 28-year follow-up in the Northern Finland 1966 birth cohort Acta Psychiatr Scand 1999 7 100 1 17 26 10442435
  13. [13]Waddell C Creativity and mental illness: is there a link? Can J Psychiatry 1998 3 43 2 166 72 9533970
  14. [14]Post F Creativity and psychopathology. A study of 291 world-famous men Br J Psychiatry 1994 7 165 1 22 34 7953036
  15. [16]Bouchard TJ Jr McGue M Familial studies of intelligence: a review Science 1981 5 29 212 4498 1055 9 7195071
  16. [17]Deary IJ Spinath FM Bates TC Genetics of intelligence Eur J Hum Genet 2006 6 14 6 690 700 16721405
  17. [18]Sullivan PF Kendler KS Neale MC Schizophrenia as a complex trait: evidence from a meta-analysis of twin studies Arch Gen Psychiatry 2003 12 60 12 1187 92 14662550
  18. [19]Luciano M Miyajima F Lind PA Bates TC Horan M Harris SE Wright MJ Ollier WE Hayward C Pendleton N Gow AJ Visscher PM Starr JM Deary IJ Martin NG Payton A Variation in the dysbindin gene and normal cognitive function in three independent population samples Genes Brain Behav 2009 3 8 2 218 27 19077176
  19. [21]Guilmatre A Dubourg C Mosca AL Legallic S Goldenberg A Drouin-Garraud V Layet V Rosier A Briault S Bonnet-Brilhault F Laumonnier F Odent S Le VG Joly-Helas G David V Bendavid C Pinoit JM Henry C Impallomeni C Germano E Tortorella G Di RG Barthelemy C Andres C Faivre L Frebourg T Saugier VP Campion D Recurrent rearrangements in synaptic and neurodevelopmental genes and shared biologic pathways in schizophrenia, autism, and mental retardation Arch Gen Psychiatry 2009 9 66 9 947 56 19736351 PMC2958844
  20. [22]Fromer M Pocklington AJ Kavanagh DH Williams HJ Dwyer S Gormley P Georgieva L Rees E Palta P Ruderfer DM Carrera N Humphreys I Johnson JS Roussos P Barker DD Banks E Milanova V Grant SG Hannon E Rose SA Chambert K Mahajan M Scolnick EM Moran JL Kirov G Palotie A McCarroll SA Holmans P Sklar P Owen MJ Purcell SM O'Donovan MC De novo mutations in schizophrenia implicate synaptic networks Nature 2014 2 13 506 7487 179 84 24463507 PMC4237002
  21. [23]Dickson H Cullen AE Reichenberg A Hodgins S Campbell DD Morris RG Laurens R Cognitive impairment among children at-risk for schizophrenia J Psychiatr Res 2014 3 50 92 9 24373930
  22. [24]Toulopoulou T Picchioni M Rijsdijk F Hua-Hall M Ettinger U Sham P Murray R Substantial genetic overlap between neurocognition and schizophrenia: genetic modeling in twin samples Arch Gen Psychiatry 2007 12 64 12 1348 55 18056542
  23. [25]Fowler T Zammit S Owen MJ Rasmussen F A population-based study of shared genetic variation between premorbid IQ and psychosis among male twin pairs and sibling pairs from Sweden Arch Gen Psychiatry 2012 5 69 5 460 6 22566578
  24. [26]Gunnell D Harrison G Rasmussen F Fouskakis D Tynelius P Associations between premorbid intellectual performance, early-life exposures and early-onset schizophrenia. Cohort study Br J Psychiatry 2002 10 181 298 305 12356656
  25. [27]Zammit S Allebeck P David AS Dalman C Hemmingsson T Lundberg I Lewis G A longitudinal study of premorbid IQ Score and risk of developing schizophrenia, bipolar disorder, severe depression, and other nonaffective psychoses Arch Gen Psychiatry 2004 4 61 4 354 60 15066893
  26. [29]Ekholm B Ekholm A Adolfsson R Vares M Osby U Sedvall GC Jonsson EG Evaluation of diagnostic procedures in Swedish patients with schizophrenia and related psychoses Nordic Journal of Psychiatry 2005 59 1 457 64 16316898

Cited by

Sorted by citations

Authors
Kendler, K. S., Ohlsson, H., Sundquist, J., & Sundquist, K.
Affiliations
Virginia Commonwealth University (US)
ORCID
Venue
American Journal of Psychiatry
Publisher
American Psychiatric Association Publishing
Published
2015-03-01
Volume
172
Issue
3
Pages
259-265
ISSN
  • 0002-953X (ISSN-L)
  • 1535-7228
DOI
10.1176/appi.ajp.2014.14040516
PMC
PMC4391822
OpenAlex
W2028689693
Cited by
102
References
2
Citations by year
2026: 5 · 2025: 3 · 2024: 10 · 2023: 1 · 2022: 8 · 2021: 8 · 2020: 10 · 2019: 14 · 2018: 17 · 2017: 11 · 2016: 8 · 2015: 7
FWCI
6.62
Type
journal article
Language
en
Open access
Locations
  • American Journal of Psychiatry (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
  • Lund University Publications (Lund University) (submittedVersion)
Funders
National Institute of Mental Health (R01MH083094)
Topics
  • Health Sciences › Medicine › Psychiatry and Mental health › Schizophrenia research and treatment
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Genetic Associations and Epidemiology
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Cognitive Abilities and Testing
Keywords
intelligence quotient, schizophrenia risk, genetic susceptibility, familial aggregation, schizophrenia onset
MeSH terms
Adolescent, Family, Humans, Intelligence, Intelligence Tests, Male, Psychiatric Status Rating Scales, Registries, Risk Factors, Schizophrenia, Schizophrenic Psychology, Sweden, Cluster Analysis, Proportional Hazards Models, Risk Assessment, Genetic Predisposition to Disease, Young Adult

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review