title: Evaluating the spectrum concept of schizophrenia in the Roscommon Family Study.
abstract: OBJECTIVE
  The authors sought to evaluate whether the pattern of schizophrenia and related disorders in probands and their relatives can be explained by a single underlying continuum of liability to the "schizophrenia spectrum."
  
  
  METHODS
  In the epidemiologically based Roscommon Family Study, the authors separately examined--in siblings, parents, and relatives of index and comparison probands--the familial aggregation and coaggregation of five hierarchically defined disorders: schizophrenia, schizoaffective disorder, schizotypal/paranoid personality disorder, other nonaffective psychoses, and psychotic affective illness. A multiple threshold model was fitted to these contingency tables by maximum likelihood.
  
  
  RESULTS
  The multiple threshold model that constrained resemblance to be the same in siblings and parents fit the data well and estimated the correlation in liability to schizophrenia spectrum disorders between probands and first-degree relatives at 0.36. Parents, however, required higher levels of liability to manifest schizophrenia spectrum disorders than siblings. While schizophrenia and psychotic affective illness could be clearly assigned to the two extremes of the schizophrenia spectrum, the proper ordering of schizoaffective disorder, schizotypal/paranoid personality disorder, and other nonaffective psychoses could not be unambiguously determined.
  
  
  CONCLUSIONS
  These results are consistent with the existence of a schizophrenia spectrum in which these five disorders are manifestations, of varying severity, of the same underlying vulnerability. This vulnerability is strongly transmitted within families.
authors.affiliation: Department of Psychiatry, Medical College of Virginia, Richmond 23298-0710, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
authors.forename: M C
authors.initials: MC
authors.lastname: Neale
authors.forename: D
authors.initials: D
authors.lastname: Walsh
mesh_terms: D000328:Adult; D000341:Affective Disorders, Psychotic / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D005190:Family; D005260:Female; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D010260:Paranoid Personality Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D015995:Prevalence; D011336:Probability; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D012042:Registries; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D012569:Schizotypal Personality Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D012720:Severity of Illness Index