title: Multidimensional assessment of impulsivity in schizophrenia, bipolar disorder, and major depressive disorder: testing for shared endophenotypes.
abstract: BACKGROUND
  Impulsivity is associated with bipolar disorder as a clinical feature during and between manic episodes and is considered a potential endophenotype for the disorder. Schizophrenia and major depressive disorder share substantial genetic overlap with bipolar disorder, and these two disorders have also been associated with elevations in impulsivity. However, little is known about the degree of overlap among these disorders in discrete subfacets of impulsivity and whether any overlap is purely phenotypic or due to shared genetic diathesis.
  
  
  METHODS
  We focused on five subfacets of impulsivity: self-reported attentional, motor, and non-planning impulsivity, self-reported sensation seeking, and a behavioral measure of motor inhibition (stop signal reaction time; SSRT). We examined these facets within and across disorder proband and co-twin groups, modeled heritability, and tested for endophenotypic patterning in a sample of twin pairs recruited from the Swedish Twin Registry (N = 420).
  
  
  RESULTS
  We found evidence of moderate to high levels of heritability for all five subfacets. All three proband groups and their unaffected co-twins showed elevations on attentional, motor, and non-planning impulsivity. Schizophrenia probands (but not their co-twins) showed significantly lower sensation seeking, and schizophrenia and bipolar disorder probands (but not in their co-twins) had significantly longer SSRTs, compared with healthy controls and the other groups.
  
  
  CONCLUSIONS
  Attentional, motor, and non-planning impulsivity emerged as potential shared endophenotypes for the three disorders, whereas sensation seeking and SSRT were associated with phenotypic affection but not genetic loading for these disorders.
authors.affiliation: Department of Psychology,Yale University,New Haven,CT,USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Fortgang
authors.affiliation: Department of Medical Epidemiology and Biostatistics,Karolinska Institutet,Stockholm,Sweden.
authors.forename: C M
authors.initials: CM
authors.lastname: Hultman
authors.affiliation: Department of Psychiatry and Human Behavior,School of Medicine, University of California,Irvine,CA,USA.
authors.forename: T G M
authors.initials: TG
authors.lastname: van Erp
authors.affiliation: Department of Psychology,Yale University,New Haven,CT,USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Cannon
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000503:physiopathology*; D003865:Major Depressive Disorder / Q000503:physiopathology*; D004200:Diseases in Twins; D058068:Endophenotypes; D005260:Female; D006801:Humans; D007175:Impulsive Behavior / Q000502:physiology*; D007266:Inhibition, Psychological; D008297:Male; D008875:Middle Aged; D012042:Registries; D012559:Schizophrenia / Q000503:physiopathology*; D013548:Sweden
keywords: Bipolar disorder; depression; endophenotype; impulsivity; inhibition; schizophrenia