title: P50 auditory evoked potential suppression in bipolar disorder patients with psychotic features and their unaffected relatives.
abstract: BACKGROUND
  Diminished suppression of the P50 response, a consistent finding in schizophrenia, has also been reported in patients with psychotic bipolar disorder. It is a promising endophenotype for schizophrenia, but its relationship to genetic liability in bipolar disorder is unknown. We therefore assessed whether diminished P50 suppression is associated with familial risk for psychotic bipolar disorder.
  
  
  METHODS
  The P50 response was collected in a conditioning (C)--testing (T) paradigm from 42 outpatients with bipolar 1 disorder who had experienced psychotic symptoms and 44 of their unaffected first-degree relatives, all from families multiply affected with bipolar disorder or another non-organic psychotic disorder; 48 healthy control subjects were also studied. The T/C ratio was compared between the groups, with linear regression analyses and robust variance estimators for clustered data.
  
  
  RESULTS
  Both patients (estimated mean difference in T/C ratio to control subjects, 32, 95% confidence interval [CI] 15-48, p=.001) and unaffected relatives (20, 95% CI 7-32, p=.002) demonstrated higher T/C ratio, thus indicating diminished P50 suppression compared with control subjects.
  
  
  CONCLUSIONS
  To our knowledge, this is the first report of diminished P50 gating in unaffected relatives of psychotic bipolar disorder patients from multiply affected families. Our results suggest that impaired P50 gating is a putative endophenotype for psychotic bipolar disorder and thus might reflect the impact of susceptibility genes across psychosis.
authors.affiliation: Section of General Psychiatry, Social, Genetic Developmental Psychiatry Research Centre, Institute of Psychiatry, King's College, London, UK, and Psychology Research Laboratory, McLean Hospital, Belmont, MA, USA. k.schulze@iop.kcl.ac.uk
authors.forename: Katja K
authors.initials: KK
authors.lastname: Schulze
authors.forename: Mei-Hua
authors.initials: MH
authors.lastname: Hall
authors.forename: Colm
authors.initials: C
authors.lastname: McDonald
authors.forename: Nicolette
authors.initials: N
authors.lastname: Marshall
authors.forename: Muriel
authors.initials: M
authors.lastname: Walshe
authors.forename: Robin M
authors.initials: RM
authors.lastname: Murray
authors.forename: Elvira
authors.initials: E
authors.lastname: Bramon
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D000553:Ambulatory Care; D001303:Auditory Cortex / Q000502:physiology; D001307:Auditory Perception / Q000502:physiology; D001714:Bipolar Disorder / Q000175:diagnosis* / Q000235:genetics* / Q000503:physiopathology*; D003213:Conditioning, Psychological / Q000502:physiology; D004569:Electroencephalography; D004585:Electrooculography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005190:Family; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D010641:Phenotype; D011618:Psychotic Disorders / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology