title: Pre-morbid IQ in mental disorders: a Danish draft-board study of 7486 psychiatric patients.
abstract: BACKGROUND
  Longitudinal studies indicate that future schizophrenia patients exhibit lower IQ than healthy controls. Recent studies suggest that future patients with other mental illnesses obtain lower pre-morbid IQ. The aims of this study were to compare pre-morbid IQ among five diagnostic categories and normal controls, to examine the distribution of pre-morbid IQ, and to investigate the relationship between pre-morbid IQ and risk of mental illness.
  
  
  METHODS
  A total of 7486 individuals hospitalized with psychiatric disease and 20 531 controls. IQ was measured at the draft board and hospital diagnoses [schizophrenia (Sz), non-schizophrenic, non-affective psychoses (NSAP), affective (AD), personality (PD) and neurotic/stress disorders (ND)] were followed up to ages 43-54 years. Individuals hospitalized < or = 1 year after appearing before the draft board were excluded.
  
  
  RESULTS
  All future patients obtained significantly lower pre-morbid IQ than controls (3-7 IQ points), AD had the highest IQ and PD the lowest. In each diagnostic category, decreasing IQ was associated with an increasing risk of becoming a patient [odds ratios (ORs) 0.5-2.5 over the full IQ spectrum]. IQ distributions was nearly normal and uni-modal.
  
  
  CONCLUSIONS
  IQ deficits in each diagnostic category may reflect different functional patterns and temporal vicissitudes of the specific pathogenetic processes involved in different mental disorders.
authors: University Department of Psychiatry, Hvidovre Hospital, 2605 Brøndby, Denmark. annickurferparnas@dadlnet.dk
authors: A
authors: A
authors: Urfer-Parnas
authors: E
authors: E
authors: Lykke Mortensen
authors: D
authors: D
authors: Saebye
authors: J
authors: J
authors: Parnas
mesh_terms: D000328:Adult; D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000453:epidemiology* / Q000534:rehabilitation; D008875:Middle Aged; D019964:Mood Disorders / Q000175:diagnosis / Q000453:epidemiology; D009483:Neuropsychological Tests; D010343:Patient Admission / Q000706:statistics & numerical data; D010554:Personality Disorders / Q000175:diagnosis / Q000453:epidemiology; D015995:Prevalence; D012042:Registries; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology; D012720:Severity of Illness Index